Auto merge of #142574 - Kobzol:rollup-ldj386u, r=Kobzol

Rollup of 12 pull requests

Successful merges:

 - rust-lang/rust#141639 (Expose discriminant values in stable_mir)
 - rust-lang/rust#142082 (Refactor `rustc_attr_data_structures` documentation)
 - rust-lang/rust#142125 (Stabilize "file_lock" feature)
 - rust-lang/rust#142236 (Add documentation for `PathBuf`'s `FromIterator` and `Extend` impls)
 - rust-lang/rust#142373 (Fix Debug for Location)
 - rust-lang/rust#142416 (Assorted bootstrap cleanups (step 2))
 - rust-lang/rust#142431 (Add initial version of snapshot tests to bootstrap)
 - rust-lang/rust#142450 (Add documentation on top of `rustc_middle/src/query/mod.rs`)
 - rust-lang/rust#142528 (clarify `rustc_do_not_const_check` comment)
 - rust-lang/rust#142530 (use `if let` guards where possible)
 - rust-lang/rust#142561 (Remove an `njn:` comment accidentaly left behind.)
 - rust-lang/rust#142566 (Fix `-nopt` CI jobs)

r? `@ghost`
`@rustbot` modify labels: rollup

40 files changed, 693 insertions, 203 deletions

diff --git a/compiler/rustc_attr_data_structures/src/attributes.rs b/compiler/rustc_attr_data_structures/src/attributes.rs
index 845e4d5e5d0..a0a50fd4b7c 100644
--- a/compiler/rustc_attr_data_structures/src/attributes.rs
+++ b/compiler/rustc_attr_data_structures/src/attributes.rs
@@ -130,24 +130,54 @@ impl Deprecation {
     }
 }
 
-/// Represent parsed, *built in*, inert attributes.
+/// Represents parsed *built-in* inert attributes.
 ///
-/// That means attributes that are not actually ever expanded.
-/// For more information on this, see the module docs on the [`rustc_attr_parsing`] crate.
-/// They're instead used as markers, to guide the compilation process in various way in most every stage of the compiler.
-/// These are kept around after the AST, into the HIR and further on.
+/// ## Overview
+/// These attributes are markers that guide the compilation process and are never expanded into other code.
+/// They persist throughout the compilation phases, from AST to HIR and beyond.
 ///
-/// The word "parsed" could be a little misleading here, because the parser already parses
-/// attributes early on. However, the result, an [`ast::Attribute`]
-/// is only parsed at a high level, still containing a token stream in many cases. That is
-/// because the structure of the contents varies from attribute to attribute.
-/// With a parsed attribute I mean that each attribute is processed individually into a
-/// final structure, which on-site (the place where the attribute is useful for, think the
-/// the place where `must_use` is checked) little to no extra parsing or validating needs to
-/// happen.
+/// ## Attribute Processing
+/// While attributes are initially parsed by [`rustc_parse`] into [`ast::Attribute`], they still contain raw token streams
+/// because different attributes have different internal structures. This enum represents the final,
+/// fully parsed form of these attributes, where each variant contains contains all the information and
+/// structure relevant for the specific attribute.
 ///
-/// For more docs, look in [`rustc_attr_parsing`].
+/// Some attributes can be applied multiple times to the same item, and they are "collapsed" into a single
+/// semantic attribute. For example:
+/// ```rust
+/// #[repr(C)]
+/// #[repr(packed)]
+/// struct S { }
+/// ```
+/// This is equivalent to `#[repr(C, packed)]` and results in a single [`AttributeKind::Repr`] containing
+/// both `C` and `packed` annotations. This collapsing happens during parsing and is reflected in the
+/// data structures defined in this enum.
 ///
+/// ## Usage
+/// These parsed attributes are used throughout the compiler to:
+/// - Control code generation (e.g., `#[repr]`)
+/// - Mark API stability (`#[stable]`, `#[unstable]`)
+/// - Provide documentation (`#[doc]`)
+/// - Guide compiler behavior (e.g., `#[allow_internal_unstable]`)
+///
+/// ## Note on Attribute Organization
+/// Some attributes like `InlineAttr`, `OptimizeAttr`, and `InstructionSetAttr` are defined separately
+/// from this enum because they are used in specific compiler phases (like code generation) and don't
+/// need to persist throughout the entire compilation process. They are typically processed and
+/// converted into their final form earlier in the compilation pipeline.
+///
+/// For example:
+/// - `InlineAttr` is used during code generation to control function inlining
+/// - `OptimizeAttr` is used to control optimization levels
+/// - `InstructionSetAttr` is used for target-specific code generation
+///
+/// These attributes are handled by their respective compiler passes in the [`rustc_codegen_ssa`] crate
+/// and don't need to be preserved in the same way as the attributes in this enum.
+///
+/// For more details on attribute parsing, see the [`rustc_attr_parsing`] crate.
+///
+/// [`rustc_parse`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/index.html
+/// [`rustc_codegen_ssa`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/index.html
 /// [`rustc_attr_parsing`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_attr_parsing/index.html
 #[derive(Clone, Debug, HashStable_Generic, Encodable, Decodable, PrintAttribute)]
 pub enum AttributeKind {
diff --git a/compiler/rustc_attr_data_structures/src/lib.rs b/compiler/rustc_attr_data_structures/src/lib.rs
index b0fc19d1cd7..f8355be09ad 100644
--- a/compiler/rustc_attr_data_structures/src/lib.rs
+++ b/compiler/rustc_attr_data_structures/src/lib.rs
@@ -1,3 +1,7 @@
+//! Data structures for representing parsed attributes in the Rust compiler.
+//! For detailed documentation about attribute processing,
+//! see [rustc_attr_parsing](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_attr_parsing/index.html).
+
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![doc(rust_logo)]
diff --git a/compiler/rustc_builtin_macros/src/test.rs b/compiler/rustc_builtin_macros/src/test.rs
index b439fa34f5b..b067578794b 100644
--- a/compiler/rustc_builtin_macros/src/test.rs
+++ b/compiler/rustc_builtin_macros/src/test.rs
@@ -118,10 +118,7 @@ pub(crate) fn expand_test_or_bench(
 
     let (item, is_stmt) = match item {
         Annotatable::Item(i) => (i, false),
-        Annotatable::Stmt(stmt) if matches!(stmt.kind, ast::StmtKind::Item(_)) => {
-            // FIXME: Use an 'if let' guard once they are implemented
-            if let ast::StmtKind::Item(i) = stmt.kind { (i, true) } else { unreachable!() }
-        }
+        Annotatable::Stmt(box ast::Stmt { kind: ast::StmtKind::Item(i), .. }) => (i, true),
         other => {
             not_testable_error(cx, attr_sp, None);
             return vec![other];
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index 311dadb53c4..7a29f8c9fbd 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -35,6 +35,7 @@ use crate::base::ast::MetaItemInner;
 use crate::errors;
 use crate::expand::{self, AstFragment, Invocation};
 use crate::module::DirOwnership;
+use crate::stats::MacroStat;
 
 // When adding new variants, make sure to
 // adjust the `visit_*` / `flat_map_*` calls in `InvocationCollector`
@@ -1191,7 +1192,7 @@ pub struct ExtCtxt<'a> {
     /// not to expand it again.
     pub(super) expanded_inert_attrs: MarkedAttrs,
     /// `-Zmacro-stats` data.
-    pub macro_stats: FxHashMap<(Symbol, MacroKind), crate::stats::MacroStat>, // njn: quals
+    pub macro_stats: FxHashMap<(Symbol, MacroKind), MacroStat>,
 }
 
 impl<'a> ExtCtxt<'a> {
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index 73a21789c5d..7d6e471e7e9 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -887,7 +887,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         rustc_legacy_const_generics, Normal, template!(List: "N"), ErrorFollowing,
         EncodeCrossCrate::Yes,
     ),
-    // Do not const-check this function's body. It will always get replaced during CTFE.
+    // Do not const-check this function's body. It will always get replaced during CTFE via `hook_special_const_fn`.
     rustc_attr!(
         rustc_do_not_const_check, Normal, template!(Word), WarnFollowing,
         EncodeCrossCrate::Yes, "`#[rustc_do_not_const_check]` skips const-check for this function's body",
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 15e8c1ef3cc..63312eff490 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1,8 +1,64 @@
-//! Defines the various compiler queries.
 //!
-//! For more information on the query system, see
-//! ["Queries: demand-driven compilation"](https://rustc-dev-guide.rust-lang.org/query.html).
-//! This chapter includes instructions for adding new queries.
+//! # The rustc Query System: Query Definitions and Modifiers
+//!
+//! The core processes in rustc are shipped as queries. Each query is a demand-driven function from some key to a value.
+//! The execution result of the function is cached and directly read during the next request, thereby improving compilation efficiency.
+//! Some results are saved locally and directly read during the next compilation, which are core of incremental compilation.
+//!
+//! ## How to Read This Module
+//!
+//! Each `query` block in this file defines a single query, specifying its key and value types, along with various modifiers.
+//! These query definitions are processed by the [`rustc_macros`], which expands them into the necessary boilerplate code
+//! for the query system—including the [`Providers`] struct (a function table for all query implementations, where each field is
+//! a function pointer to the actual provider), caching, and dependency graph integration.
+//! **Note:** The `Providers` struct is not a Rust trait, but a struct generated by the `rustc_macros` to hold all provider functions.
+//! The `rustc_macros` also supports a set of **query modifiers** (see below) that control the behavior of each query.
+//!
+//! The actual provider functions are implemented in various modules and registered into the `Providers` struct
+//! during compiler initialization (see [`rustc_interface::passes::DEFAULT_QUERY_PROVIDERS`]).
+//!
+//! [`rustc_macros`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_macros/index.html
+//! [`rustc_interface::passes::DEFAULT_QUERY_PROVIDERS`]: ../../rustc_interface/passes/static.DEFAULT_QUERY_PROVIDERS.html
+//!
+//! ## Query Modifiers
+//!
+//! Query modifiers are special flags that alter the behavior of a query. They are parsed and processed by the `rustc_macros`
+//! The main modifiers are:
+//!
+//! - `desc { ... }`: Sets the human-readable description for diagnostics and profiling. Required for every query.
+//! - `arena_cache`: Use an arena for in-memory caching of the query result.
+//! - `cache_on_disk_if { ... }`: Cache the query result to disk if the provided block evaluates to true.
+//! - `fatal_cycle`: If a dependency cycle is detected, abort compilation with a fatal error.
+//! - `cycle_delay_bug`: If a dependency cycle is detected, emit a delayed bug instead of aborting immediately.
+//! - `cycle_stash`: If a dependency cycle is detected, stash the error for later handling.
+//! - `no_hash`: Do not hash the query result for incremental compilation; just mark as dirty if recomputed.
+//! - `anon`: Make the query anonymous in the dependency graph (no dep node is created).
+//! - `eval_always`: Always evaluate the query, ignoring its dependencies and cached results.
+//! - `depth_limit`: Impose a recursion depth limit on the query to prevent stack overflows.
+//! - `separate_provide_extern`: Use separate provider functions for local and external crates.
+//! - `feedable`: Allow the query result to be set from another query ("fed" externally).
+//! - `return_result_from_ensure_ok`: When called via `tcx.ensure_ok()`, return `Result<(), ErrorGuaranteed>` instead of `()`.
+//!   If the query needs to be executed and returns an error, the error is returned to the caller.
+//!   Only valid for queries returning `Result<_, ErrorGuaranteed>`.
+//!
+//! For the up-to-date list, see the `QueryModifiers` struct in
+//! [`rustc_macros/src/query.rs`](https://github.com/rust-lang/rust/blob/master/compiler/rustc_macros/src/query.rs)
+//! and for more details in incremental compilation, see the
+//! [Query modifiers in incremental compilation](https://rustc-dev-guide.rust-lang.org/queries/incremental-compilation-in-detail.html#query-modifiers) section of the rustc-dev-guide.
+//!
+//! ## Query Expansion and Code Generation
+//!
+//! The [`rustc_macros::rustc_queries`] macro expands each query definition into:
+//! - A method on [`TyCtxt`] (and [`TyCtxtAt`]) for invoking the query.
+//! - Provider traits and structs for supplying the query's value.
+//! - Caching and dependency graph integration.
+//! - Support for incremental compilation, disk caching, and arena allocation as controlled by the modifiers.
+//!
+//! [`rustc_macros::rustc_queries`]: ../../rustc_macros/macro.rustc_queries.html
+//!
+//! The macro-based approach allows the query system to be highly flexible and maintainable, while minimizing boilerplate.
+//!
+//! For more details, see the [rustc-dev-guide](https://rustc-dev-guide.rust-lang.org/query.html).
 
 #![allow(unused_parens)]
 
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index b49a13ce584..215202c4bd5 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -2273,23 +2273,18 @@ impl<'a> Parser<'a> {
                     ),
                     // Also catches `fn foo(&a)`.
                     PatKind::Ref(ref inner_pat, mutab)
-                        if matches!(inner_pat.clone().kind, PatKind::Ident(..)) =>
+                        if let PatKind::Ident(_, ident, _) = inner_pat.clone().kind =>
                     {
-                        match inner_pat.clone().kind {
-                            PatKind::Ident(_, ident, _) => {
-                                let mutab = mutab.prefix_str();
-                                (
-                                    ident,
-                                    "self: ",
-                                    format!("{ident}: &{mutab}TypeName"),
-                                    "_: ",
-                                    pat.span.shrink_to_lo(),
-                                    pat.span,
-                                    pat.span.shrink_to_lo(),
-                                )
-                            }
-                            _ => unreachable!(),
-                        }
+                        let mutab = mutab.prefix_str();
+                        (
+                            ident,
+                            "self: ",
+                            format!("{ident}: &{mutab}TypeName"),
+                            "_: ",
+                            pat.span.shrink_to_lo(),
+                            pat.span,
+                            pat.span.shrink_to_lo(),
+                        )
                     }
                     _ => {
                         // Otherwise, try to get a type and emit a suggestion.
diff --git a/compiler/rustc_smir/src/rustc_smir/context.rs b/compiler/rustc_smir/src/rustc_smir/context.rs
index ef8c88355f6..baa4c0681e8 100644
--- a/compiler/rustc_smir/src/rustc_smir/context.rs
+++ b/compiler/rustc_smir/src/rustc_smir/context.rs
@@ -12,7 +12,8 @@ use rustc_middle::ty::layout::{
 };
 use rustc_middle::ty::print::{with_forced_trimmed_paths, with_no_trimmed_paths};
 use rustc_middle::ty::{
-    GenericPredicates, Instance, List, ScalarInt, TyCtxt, TypeVisitableExt, ValTree,
+    CoroutineArgsExt, GenericPredicates, Instance, List, ScalarInt, TyCtxt, TypeVisitableExt,
+    ValTree,
 };
 use rustc_middle::{mir, ty};
 use rustc_span::def_id::LOCAL_CRATE;
@@ -22,9 +23,9 @@ use stable_mir::mir::mono::{InstanceDef, StaticDef};
 use stable_mir::mir::{BinOp, Body, Place, UnOp};
 use stable_mir::target::{MachineInfo, MachineSize};
 use stable_mir::ty::{
-    AdtDef, AdtKind, Allocation, ClosureDef, ClosureKind, FieldDef, FnDef, ForeignDef,
-    ForeignItemKind, GenericArgs, IntrinsicDef, LineInfo, MirConst, PolyFnSig, RigidTy, Span, Ty,
-    TyConst, TyKind, UintTy, VariantDef,
+    AdtDef, AdtKind, Allocation, ClosureDef, ClosureKind, CoroutineDef, Discr, FieldDef, FnDef,
+    ForeignDef, ForeignItemKind, GenericArgs, IntrinsicDef, LineInfo, MirConst, PolyFnSig, RigidTy,
+    Span, Ty, TyConst, TyKind, UintTy, VariantDef, VariantIdx,
 };
 use stable_mir::{Crate, CrateDef, CrateItem, CrateNum, DefId, Error, Filename, ItemKind, Symbol};
 
@@ -447,6 +448,30 @@ impl<'tcx> SmirCtxt<'tcx> {
         def.internal(&mut *tables, tcx).variants().len()
     }
 
+    /// Discriminant for a given variant index of AdtDef
+    pub fn adt_discr_for_variant(&self, adt: AdtDef, variant: VariantIdx) -> Discr {
+        let mut tables = self.0.borrow_mut();
+        let tcx = tables.tcx;
+        let adt = adt.internal(&mut *tables, tcx);
+        let variant = variant.internal(&mut *tables, tcx);
+        adt.discriminant_for_variant(tcx, variant).stable(&mut *tables)
+    }
+
+    /// Discriminant for a given variand index and args of a coroutine
+    pub fn coroutine_discr_for_variant(
+        &self,
+        coroutine: CoroutineDef,
+        args: &GenericArgs,
+        variant: VariantIdx,
+    ) -> Discr {
+        let mut tables = self.0.borrow_mut();
+        let tcx = tables.tcx;
+        let coroutine = coroutine.def_id().internal(&mut *tables, tcx);
+        let args = args.internal(&mut *tables, tcx);
+        let variant = variant.internal(&mut *tables, tcx);
+        args.as_coroutine().discriminant_for_variant(coroutine, tcx, variant).stable(&mut *tables)
+    }
+
     /// The name of a variant.
     pub fn variant_name(&self, def: VariantDef) -> Symbol {
         let mut tables = self.0.borrow_mut();
diff --git a/compiler/rustc_smir/src/rustc_smir/convert/ty.rs b/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
index 6a26f5f7997..b4239ddd896 100644
--- a/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
+++ b/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
@@ -960,3 +960,11 @@ impl<'tcx> Stable<'tcx> for ty::ImplTraitInTraitData {
         }
     }
 }
+
+impl<'tcx> Stable<'tcx> for rustc_middle::ty::util::Discr<'tcx> {
+    type T = stable_mir::ty::Discr;
+
+    fn stable(&self, tables: &mut Tables<'_>) -> Self::T {
+        stable_mir::ty::Discr { val: self.val, ty: self.ty.stable(tables) }
+    }
+}
diff --git a/compiler/rustc_smir/src/stable_mir/compiler_interface.rs b/compiler/rustc_smir/src/stable_mir/compiler_interface.rs
index 3967ad13eeb..2668fba9f4f 100644
--- a/compiler/rustc_smir/src/stable_mir/compiler_interface.rs
+++ b/compiler/rustc_smir/src/stable_mir/compiler_interface.rs
@@ -13,10 +13,10 @@ use stable_mir::mir::mono::{Instance, InstanceDef, StaticDef};
 use stable_mir::mir::{BinOp, Body, Place, UnOp};
 use stable_mir::target::MachineInfo;
 use stable_mir::ty::{
-    AdtDef, AdtKind, Allocation, ClosureDef, ClosureKind, FieldDef, FnDef, ForeignDef,
-    ForeignItemKind, ForeignModule, ForeignModuleDef, GenericArgs, GenericPredicates, Generics,
-    ImplDef, ImplTrait, IntrinsicDef, LineInfo, MirConst, PolyFnSig, RigidTy, Span, TraitDecl,
-    TraitDef, Ty, TyConst, TyConstId, TyKind, UintTy, VariantDef,
+    AdtDef, AdtKind, Allocation, ClosureDef, ClosureKind, CoroutineDef, Discr, FieldDef, FnDef,
+    ForeignDef, ForeignItemKind, ForeignModule, ForeignModuleDef, GenericArgs, GenericPredicates,
+    Generics, ImplDef, ImplTrait, IntrinsicDef, LineInfo, MirConst, PolyFnSig, RigidTy, Span,
+    TraitDecl, TraitDef, Ty, TyConst, TyConstId, TyKind, UintTy, VariantDef, VariantIdx,
 };
 use stable_mir::{
     AssocItems, Crate, CrateItem, CrateItems, CrateNum, DefId, Error, Filename, ImplTraitDecls,
@@ -230,6 +230,21 @@ impl<'tcx> SmirInterface<'tcx> {
         self.cx.adt_variants_len(def)
     }
 
+    /// Discriminant for a given variant index of AdtDef
+    pub(crate) fn adt_discr_for_variant(&self, adt: AdtDef, variant: VariantIdx) -> Discr {
+        self.cx.adt_discr_for_variant(adt, variant)
+    }
+
+    /// Discriminant for a given variand index and args of a coroutine
+    pub(crate) fn coroutine_discr_for_variant(
+        &self,
+        coroutine: CoroutineDef,
+        args: &GenericArgs,
+        variant: VariantIdx,
+    ) -> Discr {
+        self.cx.coroutine_discr_for_variant(coroutine, args, variant)
+    }
+
     /// The name of a variant.
     pub(crate) fn variant_name(&self, def: VariantDef) -> Symbol {
         self.cx.variant_name(def)
diff --git a/compiler/rustc_smir/src/stable_mir/ty.rs b/compiler/rustc_smir/src/stable_mir/ty.rs
index 2934af31cd5..4415cd6e2e3 100644
--- a/compiler/rustc_smir/src/stable_mir/ty.rs
+++ b/compiler/rustc_smir/src/stable_mir/ty.rs
@@ -756,6 +756,12 @@ crate_def! {
     pub CoroutineDef;
 }
 
+impl CoroutineDef {
+    pub fn discriminant_for_variant(&self, args: &GenericArgs, idx: VariantIdx) -> Discr {
+        with(|cx| cx.coroutine_discr_for_variant(*self, args, idx))
+    }
+}
+
 crate_def! {
     #[derive(Serialize)]
     pub CoroutineClosureDef;
@@ -831,6 +837,15 @@ impl AdtDef {
     pub fn repr(&self) -> ReprOptions {
         with(|cx| cx.adt_repr(*self))
     }
+
+    pub fn discriminant_for_variant(&self, idx: VariantIdx) -> Discr {
+        with(|cx| cx.adt_discr_for_variant(*self, idx))
+    }
+}
+
+pub struct Discr {
+    pub val: u128,
+    pub ty: Ty,
 }
 
 /// Definition of a variant, which can be either a struct / union field or an enum variant.
diff --git a/library/core/src/panic/location.rs b/library/core/src/panic/location.rs
index 94cfd667ffa..f1eedede8aa 100644
--- a/library/core/src/panic/location.rs
+++ b/library/core/src/panic/location.rs
@@ -30,7 +30,7 @@ use crate::fmt;
 /// Files are compared as strings, not `Path`, which could be unexpected.
 /// See [`Location::file`]'s documentation for more discussion.
 #[lang = "panic_location"]
-#[derive(Copy, Clone, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+#[derive(Copy, Clone, Eq, Hash, Ord, PartialEq, PartialOrd)]
 #[stable(feature = "panic_hooks", since = "1.10.0")]
 pub struct Location<'a> {
     // Note: this filename will have exactly one nul byte at its end, but otherwise
@@ -43,6 +43,17 @@ pub struct Location<'a> {
     col: u32,
 }
 
+#[stable(feature = "panic_hooks", since = "1.10.0")]
+impl fmt::Debug for Location<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Location")
+            .field("file", &self.file())
+            .field("line", &self.line)
+            .field("column", &self.col)
+            .finish()
+    }
+}
+
 impl<'a> Location<'a> {
     /// Returns the source location of the caller of this function. If that function's caller is
     /// annotated then its call location will be returned, and so on up the stack to the first call
diff --git a/library/coretests/tests/panic/location.rs b/library/coretests/tests/panic/location.rs
index d20241d8380..5ce0b06e90e 100644
--- a/library/coretests/tests/panic/location.rs
+++ b/library/coretests/tests/panic/location.rs
@@ -29,3 +29,11 @@ fn location_const_column() {
     const COLUMN: u32 = CALLER.column();
     assert_eq!(COLUMN, 40);
 }
+
+#[test]
+fn location_debug() {
+    let f = format!("{:?}", Location::caller());
+    assert!(f.contains(&format!("{:?}", file!())));
+    assert!(f.contains("35"));
+    assert!(f.contains("29"));
+}
diff --git a/library/std/src/fs.rs b/library/std/src/fs.rs
index 0cd794fd3ef..865ea620a28 100644
--- a/library/std/src/fs.rs
+++ b/library/std/src/fs.rs
@@ -121,7 +121,7 @@ pub struct File {
 ///
 /// [`try_lock`]: File::try_lock
 /// [`try_lock_shared`]: File::try_lock_shared
-#[unstable(feature = "file_lock", issue = "130994")]
+#[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
 pub enum TryLockError {
     /// The lock could not be acquired due to an I/O error on the file. The standard library will
     /// not return an [`ErrorKind::WouldBlock`] error inside [`TryLockError::Error`]
@@ -366,10 +366,10 @@ pub fn write<P: AsRef<Path>, C: AsRef<[u8]>>(path: P, contents: C) -> io::Result
     inner(path.as_ref(), contents.as_ref())
 }
 
-#[unstable(feature = "file_lock", issue = "130994")]
+#[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
 impl error::Error for TryLockError {}
 
-#[unstable(feature = "file_lock", issue = "130994")]
+#[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
 impl fmt::Debug for TryLockError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
@@ -379,7 +379,7 @@ impl fmt::Debug for TryLockError {
     }
 }
 
-#[unstable(feature = "file_lock", issue = "130994")]
+#[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
 impl fmt::Display for TryLockError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
@@ -390,7 +390,7 @@ impl fmt::Display for TryLockError {
     }
 }
 
-#[unstable(feature = "file_lock", issue = "130994")]
+#[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
 impl From<TryLockError> for io::Error {
     fn from(err: TryLockError) -> io::Error {
         match err {
@@ -713,7 +713,6 @@ impl File {
     /// # Examples
     ///
     /// ```no_run
-    /// #![feature(file_lock)]
     /// use std::fs::File;
     ///
     /// fn main() -> std::io::Result<()> {
@@ -722,7 +721,7 @@ impl File {
     ///     Ok(())
     /// }
     /// ```
-    #[unstable(feature = "file_lock", issue = "130994")]
+    #[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
     pub fn lock(&self) -> io::Result<()> {
         self.inner.lock()
     }
@@ -766,7 +765,6 @@ impl File {
     /// # Examples
     ///
     /// ```no_run
-    /// #![feature(file_lock)]
     /// use std::fs::File;
     ///
     /// fn main() -> std::io::Result<()> {
@@ -775,7 +773,7 @@ impl File {
     ///     Ok(())
     /// }
     /// ```
-    #[unstable(feature = "file_lock", issue = "130994")]
+    #[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
     pub fn lock_shared(&self) -> io::Result<()> {
         self.inner.lock_shared()
     }
@@ -824,7 +822,6 @@ impl File {
     /// # Examples
     ///
     /// ```no_run
-    /// #![feature(file_lock)]
     /// use std::fs::{File, TryLockError};
     ///
     /// fn main() -> std::io::Result<()> {
@@ -840,7 +837,7 @@ impl File {
     ///     Ok(())
     /// }
     /// ```
-    #[unstable(feature = "file_lock", issue = "130994")]
+    #[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
     pub fn try_lock(&self) -> Result<(), TryLockError> {
         self.inner.try_lock()
     }
@@ -888,7 +885,6 @@ impl File {
     /// # Examples
     ///
     /// ```no_run
-    /// #![feature(file_lock)]
     /// use std::fs::{File, TryLockError};
     ///
     /// fn main() -> std::io::Result<()> {
@@ -905,7 +901,7 @@ impl File {
     ///     Ok(())
     /// }
     /// ```
-    #[unstable(feature = "file_lock", issue = "130994")]
+    #[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
     pub fn try_lock_shared(&self) -> Result<(), TryLockError> {
         self.inner.try_lock_shared()
     }
@@ -933,7 +929,6 @@ impl File {
     /// # Examples
     ///
     /// ```no_run
-    /// #![feature(file_lock)]
     /// use std::fs::File;
     ///
     /// fn main() -> std::io::Result<()> {
@@ -943,7 +938,7 @@ impl File {
     ///     Ok(())
     /// }
     /// ```
-    #[unstable(feature = "file_lock", issue = "130994")]
+    #[stable(feature = "file_lock", since = "CURRENT_RUSTC_VERSION")]
     pub fn unlock(&self) -> io::Result<()> {
         self.inner.unlock()
     }
diff --git a/library/std/src/path.rs b/library/std/src/path.rs
index 826d9f0f39d..0469db0814c 100644
--- a/library/std/src/path.rs
+++ b/library/std/src/path.rs
@@ -1882,6 +1882,19 @@ impl FromStr for PathBuf {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<P: AsRef<Path>> FromIterator<P> for PathBuf {
+    /// Creates a new `PathBuf` from the [`Path`] elements of an iterator.
+    ///
+    /// This uses [`push`](Self::push) to add each element, so can be used to adjoin multiple path
+    /// [components](Components).
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::path::PathBuf;
+    /// let path = PathBuf::from_iter(["/tmp", "foo", "bar"]);
+    /// assert_eq!(path, PathBuf::from("/tmp/foo/bar"));
+    /// ```
+    ///
+    /// See documentation for [`push`](Self::push) for more details on how the path is constructed.
     fn from_iter<I: IntoIterator<Item = P>>(iter: I) -> PathBuf {
         let mut buf = PathBuf::new();
         buf.extend(iter);
@@ -1891,6 +1904,20 @@ impl<P: AsRef<Path>> FromIterator<P> for PathBuf {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<P: AsRef<Path>> Extend<P> for PathBuf {
+    /// Extends `self` with [`Path`] elements from `iter`.
+    ///
+    /// This uses [`push`](Self::push) to add each element, so can be used to adjoin multiple path
+    /// [components](Components).
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::path::PathBuf;
+    /// let mut path = PathBuf::from("/tmp");
+    /// path.extend(["foo", "bar", "file.txt"]);
+    /// assert_eq!(path, PathBuf::from("/tmp/foo/bar/file.txt"));
+    /// ```
+    ///
+    /// See documentation for [`push`](Self::push) for more details on how the path is constructed.
     fn extend<I: IntoIterator<Item = P>>(&mut self, iter: I) {
         iter.into_iter().for_each(move |p| self.push(p.as_ref()));
     }
diff --git a/src/bootstrap/Cargo.lock b/src/bootstrap/Cargo.lock
index 0c8e6633560..a6ca699e282 100644
--- a/src/bootstrap/Cargo.lock
+++ b/src/bootstrap/Cargo.lock
@@ -44,6 +44,7 @@ dependencies = [
  "fd-lock",
  "home",
  "ignore",
+ "insta",
  "junction",
  "libc",
  "object",
@@ -159,6 +160,18 @@ dependencies = [
 ]
 
 [[package]]
+name = "console"
+version = "0.15.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "054ccb5b10f9f2cbf51eb355ca1d05c2d279ce1804688d0db74b4733a5aeafd8"
+dependencies = [
+ "encode_unicode",
+ "libc",
+ "once_cell",
+ "windows-sys 0.59.0",
+]
+
+[[package]]
 name = "cpufeatures"
 version = "0.2.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -219,6 +232,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "encode_unicode"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34aa73646ffb006b8f5147f3dc182bd4bcb190227ce861fc4a4844bf8e3cb2c0"
+
+[[package]]
 name = "errno"
 version = "0.3.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -324,6 +343,17 @@ dependencies = [
 ]
 
 [[package]]
+name = "insta"
+version = "1.43.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "154934ea70c58054b556dd430b99a98c2a7ff5309ac9891597e339b5c28f4371"
+dependencies = [
+ "console",
+ "once_cell",
+ "similar",
+]
+
+[[package]]
 name = "itoa"
 version = "1.0.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -676,6 +706,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"
 
 [[package]]
+name = "similar"
+version = "2.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbbb5d9659141646ae647b42fe094daf6c6192d1620870b449d9557f748b2daa"
+
+[[package]]
 name = "smallvec"
 version = "1.13.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/src/bootstrap/Cargo.toml b/src/bootstrap/Cargo.toml
index b12b3dfc7b2..9785a306c9b 100644
--- a/src/bootstrap/Cargo.toml
+++ b/src/bootstrap/Cargo.toml
@@ -84,6 +84,7 @@ features = [
 [dev-dependencies]
 pretty_assertions = "1.4"
 tempfile = "3.15.0"
+insta = "1.43"
 
 # We care a lot about bootstrap's compile times, so don't include debuginfo for
 # dependencies, only bootstrap itself.
diff --git a/src/bootstrap/README.md b/src/bootstrap/README.md
index f9d7c811f60..5ff999f01a9 100644
--- a/src/bootstrap/README.md
+++ b/src/bootstrap/README.md
@@ -200,6 +200,10 @@ please file issues on the [Rust issue tracker][rust-issue-tracker].
 [rust-bootstrap-zulip]: https://rust-lang.zulipchat.com/#narrow/stream/t-infra.2Fbootstrap
 [rust-issue-tracker]: https://github.com/rust-lang/rust/issues
 
+## Testing
+
+To run bootstrap tests, execute `x test bootstrap`. If you want to bless snapshot tests, then install `cargo-insta` (`cargo install cargo-insta`) and then run `cargo insta review --manifest-path src/bootstrap/Cargo.toml`.
+
 ## Changelog
 
 Because we do not release bootstrap with versions, we also do not maintain CHANGELOG files. To
diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index ebb926d81ce..f9f82b80041 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -2009,7 +2009,7 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
             // Note that if we encounter `PATH` we make sure to append to our own `PATH`
             // rather than stomp over it.
             if !builder.config.dry_run() && target.is_msvc() {
-                for (k, v) in builder.cc.borrow()[&target].env() {
+                for (k, v) in builder.cc[&target].env() {
                     if k != "PATH" {
                         cmd.env(k, v);
                     }
@@ -2026,8 +2026,7 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
             // address sanitizer enabled (e.g., ntdll.dll).
             cmd.env("ASAN_WIN_CONTINUE_ON_INTERCEPTION_FAILURE", "1");
             // Add the address sanitizer runtime to the PATH - it is located next to cl.exe.
-            let asan_runtime_path =
-                builder.cc.borrow()[&target].path().parent().unwrap().to_path_buf();
+            let asan_runtime_path = builder.cc[&target].path().parent().unwrap().to_path_buf();
             let old_path = cmd
                 .get_envs()
                 .find_map(|(k, v)| (k == "PATH").then_some(v))
@@ -3059,6 +3058,8 @@ impl Step for Bootstrap {
         cargo
             .rustflag("-Cdebuginfo=2")
             .env("CARGO_TARGET_DIR", builder.out.join("bootstrap"))
+            // Needed for insta to correctly write pending snapshots to the right directories.
+            .env("INSTA_WORKSPACE_ROOT", &builder.src)
             .env("RUSTC_BOOTSTRAP", "1");
 
         // bootstrap tests are racy on directory creation so just run them one at a time.
diff --git a/src/bootstrap/src/core/build_steps/tool.rs b/src/bootstrap/src/core/build_steps/tool.rs
index f64d67341cf..237efaefada 100644
--- a/src/bootstrap/src/core/build_steps/tool.rs
+++ b/src/bootstrap/src/core/build_steps/tool.rs
@@ -1334,7 +1334,7 @@ impl Builder<'_> {
         if compiler.host.is_msvc() {
             let curpaths = env::var_os("PATH").unwrap_or_default();
             let curpaths = env::split_paths(&curpaths).collect::<Vec<_>>();
-            for (k, v) in self.cc.borrow()[&compiler.host].env() {
+            for (k, v) in self.cc[&compiler.host].env() {
                 if k != "PATH" {
                     continue;
                 }
diff --git a/src/bootstrap/src/core/builder/cargo.rs b/src/bootstrap/src/core/builder/cargo.rs
index c6cfdb69356..0e3c3aaee0f 100644
--- a/src/bootstrap/src/core/builder/cargo.rs
+++ b/src/bootstrap/src/core/builder/cargo.rs
@@ -278,9 +278,7 @@ impl Cargo {
             self.rustdocflags.arg(&arg);
         }
 
-        if !builder.config.dry_run()
-            && builder.cc.borrow()[&target].args().iter().any(|arg| arg == "-gz")
-        {
+        if !builder.config.dry_run() && builder.cc[&target].args().iter().any(|arg| arg == "-gz") {
             self.rustflags.arg("-Clink-arg=-gz");
         }
 
diff --git a/src/bootstrap/src/core/builder/mod.rs b/src/bootstrap/src/core/builder/mod.rs
index 887db683f78..7433f0b0f3b 100644
--- a/src/bootstrap/src/core/builder/mod.rs
+++ b/src/bootstrap/src/core/builder/mod.rs
@@ -5,7 +5,7 @@ use std::fmt::{self, Debug, Write};
 use std::hash::Hash;
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
-use std::sync::LazyLock;
+use std::sync::{LazyLock, OnceLock};
 use std::time::{Duration, Instant};
 use std::{env, fs};
 
@@ -60,6 +60,9 @@ pub struct Builder<'a> {
     /// to do. For example: with `./x check foo bar` we get `paths=["foo",
     /// "bar"]`.
     pub paths: Vec<PathBuf>,
+
+    /// Cached list of submodules from self.build.src.
+    submodule_paths_cache: OnceLock<Vec<String>>,
 }
 
 impl Deref for Builder<'_> {
@@ -687,7 +690,7 @@ impl<'a> ShouldRun<'a> {
     ///
     /// [`path`]: ShouldRun::path
     pub fn paths(mut self, paths: &[&str]) -> Self {
-        let submodules_paths = build_helper::util::parse_gitmodules(&self.builder.src);
+        let submodules_paths = self.builder.submodule_paths();
 
         self.paths.insert(PathSet::Set(
             paths
@@ -1180,6 +1183,7 @@ impl<'a> Builder<'a> {
             stack: RefCell::new(Vec::new()),
             time_spent_on_dependencies: Cell::new(Duration::new(0, 0)),
             paths,
+            submodule_paths_cache: Default::default(),
         }
     }
 
@@ -1510,6 +1514,19 @@ impl<'a> Builder<'a> {
         None
     }
 
+    /// Updates all submodules, and exits with an error if submodule
+    /// management is disabled and the submodule does not exist.
+    pub fn require_and_update_all_submodules(&self) {
+        for submodule in self.submodule_paths() {
+            self.require_submodule(submodule, None);
+        }
+    }
+
+    /// Get all submodules from the src directory.
+    pub fn submodule_paths(&self) -> &[String] {
+        self.submodule_paths_cache.get_or_init(|| build_helper::util::parse_gitmodules(&self.src))
+    }
+
     /// Ensure that a given step is built, returning its output. This will
     /// cache the step, so it is safe (and good!) to call this as often as
     /// needed to ensure that all dependencies are built.
diff --git a/src/bootstrap/src/core/builder/tests.rs b/src/bootstrap/src/core/builder/tests.rs
index a26a96f2815..d07df7f4a84 100644
--- a/src/bootstrap/src/core/builder/tests.rs
+++ b/src/bootstrap/src/core/builder/tests.rs
@@ -15,11 +15,12 @@ static TEST_TRIPLE_2: &str = "i686-unknown-hurd-gnu";
 static TEST_TRIPLE_3: &str = "i686-unknown-netbsd";
 
 fn configure(cmd: &str, host: &[&str], target: &[&str]) -> Config {
-    configure_with_args(&[cmd.to_owned()], host, target)
+    configure_with_args(&[cmd], host, target)
 }
 
-fn configure_with_args(cmd: &[String], host: &[&str], target: &[&str]) -> Config {
-    let mut config = Config::parse(Flags::parse(cmd));
+fn configure_with_args(cmd: &[&str], host: &[&str], target: &[&str]) -> Config {
+    let cmd = cmd.iter().copied().map(String::from).collect::<Vec<_>>();
+    let mut config = Config::parse(Flags::parse(&cmd));
     // don't save toolstates
     config.save_toolstates = None;
     config.set_dry_run(DryRun::SelfCheck);
@@ -67,7 +68,7 @@ fn run_build(paths: &[PathBuf], config: Config) -> Cache {
 fn check_cli<const N: usize>(paths: [&str; N]) {
     run_build(
         &paths.map(PathBuf::from),
-        configure_with_args(&paths.map(String::from), &[TEST_TRIPLE_1], &[TEST_TRIPLE_1]),
+        configure_with_args(&paths, &[TEST_TRIPLE_1], &[TEST_TRIPLE_1]),
     );
 }
 
@@ -1000,8 +1001,7 @@ mod sysroot_target_dirs {
 /// cg_gcc tests instead.
 #[test]
 fn test_test_compiler() {
-    let cmd = &["test", "compiler"].map(str::to_owned);
-    let config = configure_with_args(cmd, &[TEST_TRIPLE_1], &[TEST_TRIPLE_1]);
+    let config = configure_with_args(&["test", "compiler"], &[TEST_TRIPLE_1], &[TEST_TRIPLE_1]);
     let cache = run_build(&config.paths.clone(), config);
 
     let compiler = cache.contains::<test::CrateLibrustc>();
@@ -1034,8 +1034,7 @@ fn test_test_coverage() {
         // Print each test case so that if one fails, the most recently printed
         // case is the one that failed.
         println!("Testing case: {cmd:?}");
-        let cmd = cmd.iter().copied().map(str::to_owned).collect::<Vec<_>>();
-        let config = configure_with_args(&cmd, &[TEST_TRIPLE_1], &[TEST_TRIPLE_1]);
+        let config = configure_with_args(cmd, &[TEST_TRIPLE_1], &[TEST_TRIPLE_1]);
         let mut cache = run_build(&config.paths.clone(), config);
 
         let modes =
@@ -1207,8 +1206,7 @@ fn test_get_tool_rustc_compiler() {
 /// of `Any { .. }`.
 #[test]
 fn step_cycle_debug() {
-    let cmd = ["run", "cyclic-step"].map(str::to_owned);
-    let config = configure_with_args(&cmd, &[TEST_TRIPLE_1], &[TEST_TRIPLE_1]);
+    let config = configure_with_args(&["run", "cyclic-step"], &[TEST_TRIPLE_1], &[TEST_TRIPLE_1]);
 
     let err = panic::catch_unwind(|| run_build(&config.paths.clone(), config)).unwrap_err();
     let err = err.downcast_ref::<String>().unwrap().as_str();
@@ -1233,3 +1231,81 @@ fn any_debug() {
     // Downcasting to the underlying type should succeed.
     assert_eq!(x.downcast_ref::<MyStruct>(), Some(&MyStruct { x: 7 }));
 }
+
+/// The staging tests use insta for snapshot testing.
+/// See bootstrap's README on how to bless the snapshots.
+mod staging {
+    use crate::core::builder::tests::{
+        TEST_TRIPLE_1, configure, configure_with_args, render_steps, run_build,
+    };
+
+    #[test]
+    fn build_compiler_stage_1() {
+        let mut cache = run_build(
+            &["compiler".into()],
+            configure_with_args(&["build", "--stage", "1"], &[TEST_TRIPLE_1], &[TEST_TRIPLE_1]),
+        );
+        let steps = cache.into_executed_steps();
+        insta::assert_snapshot!(render_steps(&steps), @r"
+        [build] rustc 0 <target1> -> std 0 <target1>
+        [build] llvm <target1>
+        [build] rustc 0 <target1> -> rustc 1 <target1>
+        [build] rustc 0 <target1> -> rustc 1 <target1>
+        ");
+    }
+}
+
+/// Renders the executed bootstrap steps for usage in snapshot tests with insta.
+/// Only renders certain important steps.
+/// Each value in `steps` should be a tuple of (Step, step output).
+fn render_steps(steps: &[(Box<dyn Any>, Box<dyn Any>)]) -> String {
+    steps
+        .iter()
+        .filter_map(|(step, output)| {
+            // FIXME: implement an optional method on Step to produce metadata for test, instead
+            // of this downcasting
+            if let Some((rustc, output)) = downcast_step::<compile::Rustc>(step, output) {
+                Some(format!(
+                    "[build] {} -> {}",
+                    render_compiler(rustc.build_compiler),
+                    // FIXME: return the correct stage from the `Rustc` step, now it behaves weirdly
+                    render_compiler(Compiler::new(rustc.build_compiler.stage + 1, rustc.target)),
+                ))
+            } else if let Some((std, output)) = downcast_step::<compile::Std>(step, output) {
+                Some(format!(
+                    "[build] {} -> std {} <{}>",
+                    render_compiler(std.compiler),
+                    std.compiler.stage,
+                    std.target
+                ))
+            } else if let Some((llvm, output)) = downcast_step::<llvm::Llvm>(step, output) {
+                Some(format!("[build] llvm <{}>", llvm.target))
+            } else {
+                None
+            }
+        })
+        .map(|line| {
+            line.replace(TEST_TRIPLE_1, "target1")
+                .replace(TEST_TRIPLE_2, "target2")
+                .replace(TEST_TRIPLE_3, "target3")
+        })
+        .collect::<Vec<_>>()
+        .join("\n")
+}
+
+fn downcast_step<'a, S: Step>(
+    step: &'a Box<dyn Any>,
+    output: &'a Box<dyn Any>,
+) -> Option<(&'a S, &'a S::Output)> {
+    let Some(step) = step.downcast_ref::<S>() else {
+        return None;
+    };
+    let Some(output) = output.downcast_ref::<S::Output>() else {
+        return None;
+    };
+    Some((step, output))
+}
+
+fn render_compiler(compiler: Compiler) -> String {
+    format!("rustc {} <{}>", compiler.stage, compiler.host)
+}
diff --git a/src/bootstrap/src/lib.rs b/src/bootstrap/src/lib.rs
index 7254c653a2d..f1628f34dda 100644
--- a/src/bootstrap/src/lib.rs
+++ b/src/bootstrap/src/lib.rs
@@ -17,7 +17,7 @@
 //! also check out the `src/bootstrap/README.md` file for more information.
 #![cfg_attr(test, allow(unused))]
 
-use std::cell::{Cell, RefCell};
+use std::cell::Cell;
 use std::collections::{BTreeSet, HashMap, HashSet};
 use std::fmt::Display;
 use std::path::{Path, PathBuf};
@@ -189,10 +189,12 @@ pub struct Build {
 
     // Runtime state filled in later on
     // C/C++ compilers and archiver for all targets
-    cc: RefCell<HashMap<TargetSelection, cc::Tool>>,
-    cxx: RefCell<HashMap<TargetSelection, cc::Tool>>,
-    ar: RefCell<HashMap<TargetSelection, PathBuf>>,
-    ranlib: RefCell<HashMap<TargetSelection, PathBuf>>,
+    cc: HashMap<TargetSelection, cc::Tool>,
+    cxx: HashMap<TargetSelection, cc::Tool>,
+    ar: HashMap<TargetSelection, PathBuf>,
+    ranlib: HashMap<TargetSelection, PathBuf>,
+    wasi_sdk_path: Option<PathBuf>,
+
     // Miscellaneous
     // allow bidirectional lookups: both name -> path and path -> name
     crates: HashMap<String, Crate>,
@@ -466,10 +468,11 @@ impl Build {
             enzyme_info,
             in_tree_llvm_info,
             in_tree_gcc_info,
-            cc: RefCell::new(HashMap::new()),
-            cxx: RefCell::new(HashMap::new()),
-            ar: RefCell::new(HashMap::new()),
-            ranlib: RefCell::new(HashMap::new()),
+            cc: HashMap::new(),
+            cxx: HashMap::new(),
+            ar: HashMap::new(),
+            ranlib: HashMap::new(),
+            wasi_sdk_path: env::var_os("WASI_SDK_PATH").map(PathBuf::from),
             crates: HashMap::new(),
             crate_paths: HashMap::new(),
             is_sudo,
@@ -498,7 +501,7 @@ impl Build {
         }
 
         build.verbose(|| println!("finding compilers"));
-        utils::cc_detect::find(&build);
+        utils::cc_detect::fill_compilers(&mut build);
         // When running `setup`, the profile is about to change, so any requirements we have now may
         // be different on the next invocation. Don't check for them until the next time x.py is
         // run. This is ok because `setup` never runs any build commands, so it won't fail if commands are missing.
@@ -593,14 +596,6 @@ impl Build {
         }
     }
 
-    /// Updates all submodules, and exits with an error if submodule
-    /// management is disabled and the submodule does not exist.
-    pub fn require_and_update_all_submodules(&self) {
-        for submodule in build_helper::util::parse_gitmodules(&self.src) {
-            self.require_submodule(submodule, None);
-        }
-    }
-
     /// If any submodule has been initialized already, sync it unconditionally.
     /// This avoids contributors checking in a submodule change by accident.
     fn update_existing_submodules(&self) {
@@ -1143,17 +1138,17 @@ impl Build {
         if self.config.dry_run() {
             return PathBuf::new();
         }
-        self.cc.borrow()[&target].path().into()
+        self.cc[&target].path().into()
     }
 
     /// Returns the internal `cc::Tool` for the C compiler.
     fn cc_tool(&self, target: TargetSelection) -> Tool {
-        self.cc.borrow()[&target].clone()
+        self.cc[&target].clone()
     }
 
     /// Returns the internal `cc::Tool` for the C++ compiler.
     fn cxx_tool(&self, target: TargetSelection) -> Tool {
-        self.cxx.borrow()[&target].clone()
+        self.cxx[&target].clone()
     }
 
     /// Returns C flags that `cc-rs` thinks should be enabled for the
@@ -1163,8 +1158,8 @@ impl Build {
             return Vec::new();
         }
         let base = match c {
-            CLang::C => self.cc.borrow()[&target].clone(),
-            CLang::Cxx => self.cxx.borrow()[&target].clone(),
+            CLang::C => self.cc[&target].clone(),
+            CLang::Cxx => self.cxx[&target].clone(),
         };
 
         // Filter out -O and /O (the optimization flags) that we picked up
@@ -1217,7 +1212,7 @@ impl Build {
         if self.config.dry_run() {
             return None;
         }
-        self.ar.borrow().get(&target).cloned()
+        self.ar.get(&target).cloned()
     }
 
     /// Returns the path to the `ranlib` utility for the target specified.
@@ -1225,7 +1220,7 @@ impl Build {
         if self.config.dry_run() {
             return None;
         }
-        self.ranlib.borrow().get(&target).cloned()
+        self.ranlib.get(&target).cloned()
     }
 
     /// Returns the path to the C++ compiler for the target specified.
@@ -1233,7 +1228,7 @@ impl Build {
         if self.config.dry_run() {
             return Ok(PathBuf::new());
         }
-        match self.cxx.borrow().get(&target) {
+        match self.cxx.get(&target) {
             Some(p) => Ok(p.path().into()),
             None => Err(format!("target `{target}` is not configured as a host, only as a target")),
         }
@@ -1250,7 +1245,7 @@ impl Build {
         } else if target.contains("vxworks") {
             // need to use CXX compiler as linker to resolve the exception functions
             // that are only existed in CXX libraries
-            Some(self.cxx.borrow()[&target].path().into())
+            Some(self.cxx[&target].path().into())
         } else if !self.config.is_host_target(target)
             && helpers::use_host_linker(target)
             && !target.is_msvc()
diff --git a/src/bootstrap/src/utils/build_stamp/tests.rs b/src/bootstrap/src/utils/build_stamp/tests.rs
index 2d7d1f71246..f150266159a 100644
--- a/src/bootstrap/src/utils/build_stamp/tests.rs
+++ b/src/bootstrap/src/utils/build_stamp/tests.rs
@@ -1,32 +1,28 @@
 use std::path::PathBuf;
 
-use crate::{BuildStamp, Config, Flags};
+use tempfile::TempDir;
 
-fn temp_dir() -> PathBuf {
-    let config =
-        Config::parse(Flags::parse(&["check".to_owned(), "--config=/does/not/exist".to_owned()]));
-    config.tempdir()
-}
+use crate::{BuildStamp, Config, Flags};
 
 #[test]
 #[should_panic(expected = "prefix can not start or end with '.'")]
 fn test_with_invalid_prefix() {
-    let dir = temp_dir();
-    BuildStamp::new(&dir).with_prefix(".invalid");
+    let dir = TempDir::new().unwrap();
+    BuildStamp::new(dir.path()).with_prefix(".invalid");
 }
 
 #[test]
 #[should_panic(expected = "prefix can not start or end with '.'")]
 fn test_with_invalid_prefix2() {
-    let dir = temp_dir();
-    BuildStamp::new(&dir).with_prefix("invalid.");
+    let dir = TempDir::new().unwrap();
+    BuildStamp::new(dir.path()).with_prefix("invalid.");
 }
 
 #[test]
 fn test_is_up_to_date() {
-    let dir = temp_dir();
+    let dir = TempDir::new().unwrap();
 
-    let mut build_stamp = BuildStamp::new(&dir).add_stamp("v1.0.0");
+    let mut build_stamp = BuildStamp::new(dir.path()).add_stamp("v1.0.0");
     build_stamp.write().unwrap();
 
     assert!(
@@ -45,9 +41,9 @@ fn test_is_up_to_date() {
 
 #[test]
 fn test_with_prefix() {
-    let dir = temp_dir();
+    let dir = TempDir::new().unwrap();
 
-    let stamp = BuildStamp::new(&dir).add_stamp("v1.0.0");
+    let stamp = BuildStamp::new(dir.path()).add_stamp("v1.0.0");
     assert_eq!(stamp.path.file_name().unwrap(), ".stamp");
 
     let stamp = stamp.with_prefix("test");
diff --git a/src/bootstrap/src/utils/cache.rs b/src/bootstrap/src/utils/cache.rs
index 46eeffad88c..0c737470958 100644
--- a/src/bootstrap/src/utils/cache.rs
+++ b/src/bootstrap/src/utils/cache.rs
@@ -17,6 +17,7 @@ use std::borrow::Borrow;
 use std::cell::RefCell;
 use std::cmp::Ordering;
 use std::collections::HashMap;
+use std::fmt::Debug;
 use std::hash::{Hash, Hasher};
 use std::marker::PhantomData;
 use std::ops::Deref;
@@ -208,25 +209,30 @@ pub static INTERNER: LazyLock<Interner> = LazyLock::new(Interner::default);
 /// any type in its output. It is a write-once cache; values are never evicted,
 /// which means that references to the value can safely be returned from the
 /// `get()` method.
-#[derive(Debug)]
-pub struct Cache(
-    RefCell<
+#[derive(Debug, Default)]
+pub struct Cache {
+    cache: RefCell<
         HashMap<
             TypeId,
             Box<dyn Any>, // actually a HashMap<Step, Interned<Step::Output>>
         >,
     >,
-);
+    #[cfg(test)]
+    /// Contains steps in the same order in which they were executed
+    /// Useful for tests
+    /// Tuples (step, step output)
+    executed_steps: RefCell<Vec<(Box<dyn Any>, Box<dyn Any>)>>,
+}
 
 impl Cache {
     /// Creates a new empty cache.
     pub fn new() -> Cache {
-        Cache(RefCell::new(HashMap::new()))
+        Cache::default()
     }
 
     /// Stores the result of a computation step in the cache.
     pub fn put<S: Step>(&self, step: S, value: S::Output) {
-        let mut cache = self.0.borrow_mut();
+        let mut cache = self.cache.borrow_mut();
         let type_id = TypeId::of::<S>();
         let stepcache = cache
             .entry(type_id)
@@ -234,12 +240,20 @@ impl Cache {
             .downcast_mut::<HashMap<S, S::Output>>()
             .expect("invalid type mapped");
         assert!(!stepcache.contains_key(&step), "processing {step:?} a second time");
+
+        #[cfg(test)]
+        {
+            let step: Box<dyn Any> = Box::new(step.clone());
+            let output: Box<dyn Any> = Box::new(value.clone());
+            self.executed_steps.borrow_mut().push((step, output));
+        }
+
         stepcache.insert(step, value);
     }
 
     /// Retrieves a cached result for the given step, if available.
     pub fn get<S: Step>(&self, step: &S) -> Option<S::Output> {
-        let mut cache = self.0.borrow_mut();
+        let mut cache = self.cache.borrow_mut();
         let type_id = TypeId::of::<S>();
         let stepcache = cache
             .entry(type_id)
@@ -252,8 +266,8 @@ impl Cache {
 
 #[cfg(test)]
 impl Cache {
-    pub fn all<S: Ord + Clone + Step>(&mut self) -> Vec<(S, S::Output)> {
-        let cache = self.0.get_mut();
+    pub fn all<S: Ord + Step>(&mut self) -> Vec<(S, S::Output)> {
+        let cache = self.cache.get_mut();
         let type_id = TypeId::of::<S>();
         let mut v = cache
             .remove(&type_id)
@@ -265,7 +279,12 @@ impl Cache {
     }
 
     pub fn contains<S: Step>(&self) -> bool {
-        self.0.borrow().contains_key(&TypeId::of::<S>())
+        self.cache.borrow().contains_key(&TypeId::of::<S>())
+    }
+
+    #[cfg(test)]
+    pub fn into_executed_steps(mut self) -> Vec<(Box<dyn Any>, Box<dyn Any>)> {
+        mem::take(&mut self.executed_steps.borrow_mut())
     }
 }
 
diff --git a/src/bootstrap/src/utils/cc_detect.rs b/src/bootstrap/src/utils/cc_detect.rs
index 851bb38074e..dcafeb80f90 100644
--- a/src/bootstrap/src/utils/cc_detect.rs
+++ b/src/bootstrap/src/utils/cc_detect.rs
@@ -61,8 +61,8 @@ fn new_cc_build(build: &Build, target: TargetSelection) -> cc::Build {
 ///
 /// This function determines which targets need a C compiler (and, if needed, a C++ compiler)
 /// by combining the primary build target, host targets, and any additional targets. For
-/// each target, it calls [`find_target`] to configure the necessary compiler tools.
-pub fn find(build: &Build) {
+/// each target, it calls [`fill_target_compiler`] to configure the necessary compiler tools.
+pub fn fill_compilers(build: &mut Build) {
     let targets: HashSet<_> = match build.config.cmd {
         // We don't need to check cross targets for these commands.
         crate::Subcommand::Clean { .. }
@@ -87,7 +87,7 @@ pub fn find(build: &Build) {
     };
 
     for target in targets.into_iter() {
-        find_target(build, target);
+        fill_target_compiler(build, target);
     }
 }
 
@@ -96,7 +96,7 @@ pub fn find(build: &Build) {
 /// This function uses both user-specified configuration (from `bootstrap.toml`) and auto-detection
 /// logic to determine the correct C/C++ compilers for the target. It also determines the appropriate
 /// archiver (`ar`) and sets up additional compilation flags (both handled and unhandled).
-pub fn find_target(build: &Build, target: TargetSelection) {
+pub fn fill_target_compiler(build: &mut Build, target: TargetSelection) {
     let mut cfg = new_cc_build(build, target);
     let config = build.config.target_config.get(&target);
     if let Some(cc) = config
@@ -113,7 +113,7 @@ pub fn find_target(build: &Build, target: TargetSelection) {
         cfg.try_get_archiver().map(|c| PathBuf::from(c.get_program())).ok()
     };
 
-    build.cc.borrow_mut().insert(target, compiler.clone());
+    build.cc.insert(target, compiler.clone());
     let mut cflags = build.cc_handled_clags(target, CLang::C);
     cflags.extend(build.cc_unhandled_cflags(target, GitRepo::Rustc, CLang::C));
 
@@ -135,7 +135,7 @@ pub fn find_target(build: &Build, target: TargetSelection) {
     // for VxWorks, record CXX compiler which will be used in lib.rs:linker()
     if cxx_configured || target.contains("vxworks") {
         let compiler = cfg.get_compiler();
-        build.cxx.borrow_mut().insert(target, compiler);
+        build.cxx.insert(target, compiler);
     }
 
     build.verbose(|| println!("CC_{} = {:?}", target.triple, build.cc(target)));
@@ -148,11 +148,11 @@ pub fn find_target(build: &Build, target: TargetSelection) {
     }
     if let Some(ar) = ar {
         build.verbose(|| println!("AR_{} = {ar:?}", target.triple));
-        build.ar.borrow_mut().insert(target, ar);
+        build.ar.insert(target, ar);
     }
 
     if let Some(ranlib) = config.and_then(|c| c.ranlib.clone()) {
-        build.ranlib.borrow_mut().insert(target, ranlib);
+        build.ranlib.insert(target, ranlib);
     }
 }
 
@@ -221,7 +221,10 @@ fn default_compiler(
         }
 
         t if t.contains("-wasi") => {
-            let root = PathBuf::from(std::env::var_os("WASI_SDK_PATH")?);
+            let root = build
+                .wasi_sdk_path
+                .as_ref()
+                .expect("WASI_SDK_PATH mut be configured for a -wasi target");
             let compiler = match compiler {
                 Language::C => format!("{t}-clang"),
                 Language::CPlusPlus => format!("{t}-clang++"),
diff --git a/src/bootstrap/src/utils/cc_detect/tests.rs b/src/bootstrap/src/utils/cc_detect/tests.rs
index 1f50738959f..bed03c18aaa 100644
--- a/src/bootstrap/src/utils/cc_detect/tests.rs
+++ b/src/bootstrap/src/utils/cc_detect/tests.rs
@@ -77,11 +77,11 @@ fn test_new_cc_build() {
 
 #[test]
 fn test_default_compiler_wasi() {
-    let build = Build::new(Config { ..Config::parse(Flags::parse(&["build".to_owned()])) });
+    let mut build = Build::new(Config { ..Config::parse(Flags::parse(&["build".to_owned()])) });
     let target = TargetSelection::from_user("wasm32-wasi");
     let wasi_sdk = PathBuf::from("/wasi-sdk");
-    // SAFETY: bootstrap tests run on a single thread
-    unsafe { env::set_var("WASI_SDK_PATH", &wasi_sdk) };
+    build.wasi_sdk_path = Some(wasi_sdk.clone());
+
     let mut cfg = cc::Build::new();
     if let Some(result) = default_compiler(&mut cfg, Language::C, target.clone(), &build) {
         let expected = {
@@ -94,10 +94,6 @@ fn test_default_compiler_wasi() {
             "default_compiler should return a compiler path for wasi target when WASI_SDK_PATH is set"
         );
     }
-    // SAFETY: bootstrap tests run on a single thread
-    unsafe {
-        env::remove_var("WASI_SDK_PATH");
-    }
 }
 
 #[test]
@@ -119,18 +115,14 @@ fn test_find_target_with_config() {
     target_config.ar = Some(PathBuf::from("dummy-ar"));
     target_config.ranlib = Some(PathBuf::from("dummy-ranlib"));
     build.config.target_config.insert(target.clone(), target_config);
-    find_target(&build, target.clone());
-    let binding = build.cc.borrow();
-    let cc_tool = binding.get(&target).unwrap();
+    fill_target_compiler(&mut build, target.clone());
+    let cc_tool = build.cc.get(&target).unwrap();
     assert_eq!(cc_tool.path(), &PathBuf::from("dummy-cc"));
-    let binding = build.cxx.borrow();
-    let cxx_tool = binding.get(&target).unwrap();
+    let cxx_tool = build.cxx.get(&target).unwrap();
     assert_eq!(cxx_tool.path(), &PathBuf::from("dummy-cxx"));
-    let binding = build.ar.borrow();
-    let ar = binding.get(&target).unwrap();
+    let ar = build.ar.get(&target).unwrap();
     assert_eq!(ar, &PathBuf::from("dummy-ar"));
-    let binding = build.ranlib.borrow();
-    let ranlib = binding.get(&target).unwrap();
+    let ranlib = build.ranlib.get(&target).unwrap();
     assert_eq!(ranlib, &PathBuf::from("dummy-ranlib"));
 }
 
@@ -139,12 +131,12 @@ fn test_find_target_without_config() {
     let mut build = Build::new(Config { ..Config::parse(Flags::parse(&["build".to_owned()])) });
     let target = TargetSelection::from_user("x86_64-unknown-linux-gnu");
     build.config.target_config.clear();
-    find_target(&build, target.clone());
-    assert!(build.cc.borrow().contains_key(&target));
+    fill_target_compiler(&mut build, target.clone());
+    assert!(build.cc.contains_key(&target));
     if !target.triple.contains("vxworks") {
-        assert!(build.cxx.borrow().contains_key(&target));
+        assert!(build.cxx.contains_key(&target));
     }
-    assert!(build.ar.borrow().contains_key(&target));
+    assert!(build.ar.contains_key(&target));
 }
 
 #[test]
@@ -154,8 +146,8 @@ fn test_find() {
     let target2 = TargetSelection::from_user("x86_64-unknown-openbsd");
     build.targets.push(target1.clone());
     build.hosts.push(target2.clone());
-    find(&build);
+    fill_compilers(&mut build);
     for t in build.hosts.iter().chain(build.targets.iter()).chain(iter::once(&build.host_target)) {
-        assert!(build.cc.borrow().contains_key(t), "CC not set for target {}", t.triple);
+        assert!(build.cc.contains_key(t), "CC not set for target {}", t.triple);
     }
 }
diff --git a/src/bootstrap/src/utils/helpers.rs b/src/bootstrap/src/utils/helpers.rs
index 8b2f2dd431e..f4be22f1e64 100644
--- a/src/bootstrap/src/utils/helpers.rs
+++ b/src/bootstrap/src/utils/helpers.rs
@@ -98,7 +98,7 @@ pub fn is_dylib(path: &Path) -> bool {
 
 /// Return the path to the containing submodule if available.
 pub fn submodule_path_of(builder: &Builder<'_>, path: &str) -> Option<String> {
-    let submodule_paths = build_helper::util::parse_gitmodules(&builder.src);
+    let submodule_paths = builder.submodule_paths();
     submodule_paths.iter().find_map(|submodule_path| {
         if path.starts_with(submodule_path) { Some(submodule_path.to_string()) } else { None }
     })
diff --git a/src/bootstrap/src/utils/shared_helpers.rs b/src/bootstrap/src/utils/shared_helpers.rs
index 561af34a447..9c6b4a7615d 100644
--- a/src/bootstrap/src/utils/shared_helpers.rs
+++ b/src/bootstrap/src/utils/shared_helpers.rs
@@ -6,6 +6,9 @@
 
 #![allow(dead_code)]
 
+#[cfg(test)]
+mod tests;
+
 use std::env;
 use std::ffi::OsString;
 use std::fs::OpenOptions;
diff --git a/src/bootstrap/src/utils/tests/shared_helpers_tests.rs b/src/bootstrap/src/utils/shared_helpers/tests.rs
index 6c47e7f2438..559e9f70abd 100644
--- a/src/bootstrap/src/utils/tests/shared_helpers_tests.rs
+++ b/src/bootstrap/src/utils/shared_helpers/tests.rs
@@ -1,10 +1,3 @@
-//! The `shared_helpers` module can't have its own tests submodule, because
-//! that would cause problems for the shim binaries that include it via
-//! `#[path]`, so instead those unit tests live here.
-//!
-//! To prevent tidy from complaining about this file not being named `tests.rs`,
-//! it lives inside a submodule directory named `tests`.
-
 use crate::utils::shared_helpers::parse_value_from_args;
 
 #[test]
diff --git a/src/bootstrap/src/utils/tests/mod.rs b/src/bootstrap/src/utils/tests/mod.rs
index 73d55db994c..73c500f6e36 100644
--- a/src/bootstrap/src/utils/tests/mod.rs
+++ b/src/bootstrap/src/utils/tests/mod.rs
@@ -1,2 +1,3 @@
+//! This module contains shared utilities for bootstrap tests.
+
 pub mod git;
-mod shared_helpers_tests;
diff --git a/src/build_helper/src/util.rs b/src/build_helper/src/util.rs
index 72c05c4c48a..80dd6813d13 100644
--- a/src/build_helper/src/util.rs
+++ b/src/build_helper/src/util.rs
@@ -2,7 +2,6 @@ use std::fs::File;
 use std::io::{BufRead, BufReader};
 use std::path::Path;
 use std::process::Command;
-use std::sync::OnceLock;
 
 /// Invokes `build_helper::util::detail_exit` with `cfg!(test)`
 ///
@@ -51,25 +50,20 @@ pub fn try_run(cmd: &mut Command, print_cmd_on_fail: bool) -> Result<(), ()> {
 }
 
 /// Returns the submodule paths from the `.gitmodules` file in the given directory.
-pub fn parse_gitmodules(target_dir: &Path) -> &[String] {
-    static SUBMODULES_PATHS: OnceLock<Vec<String>> = OnceLock::new();
+pub fn parse_gitmodules(target_dir: &Path) -> Vec<String> {
     let gitmodules = target_dir.join(".gitmodules");
     assert!(gitmodules.exists(), "'{}' file is missing.", gitmodules.display());
 
-    let init_submodules_paths = || {
-        let file = File::open(gitmodules).unwrap();
+    let file = File::open(gitmodules).unwrap();
 
-        let mut submodules_paths = vec![];
-        for line in BufReader::new(file).lines().map_while(Result::ok) {
-            let line = line.trim();
-            if line.starts_with("path") {
-                let actual_path = line.split(' ').last().expect("Couldn't get value of path");
-                submodules_paths.push(actual_path.to_owned());
-            }
+    let mut submodules_paths = vec![];
+    for line in BufReader::new(file).lines().map_while(Result::ok) {
+        let line = line.trim();
+        if line.starts_with("path") {
+            let actual_path = line.split(' ').last().expect("Couldn't get value of path");
+            submodules_paths.push(actual_path.to_owned());
         }
+    }
 
-        submodules_paths
-    };
-
-    SUBMODULES_PATHS.get_or_init(|| init_submodules_paths())
+    submodules_paths
 }
diff --git a/src/ci/docker/host-x86_64/i686-gnu-nopt/Dockerfile b/src/ci/docker/host-x86_64/i686-gnu-nopt/Dockerfile
index 241199d3baf..58e66fd637a 100644
--- a/src/ci/docker/host-x86_64/i686-gnu-nopt/Dockerfile
+++ b/src/ci/docker/host-x86_64/i686-gnu-nopt/Dockerfile
@@ -22,10 +22,6 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
-RUN mkdir -p /config
-RUN echo "[rust]" > /config/nopt-std-config.toml
-RUN echo "optimize = false" >> /config/nopt-std-config.toml
-
 ENV RUST_CONFIGURE_ARGS --build=i686-unknown-linux-gnu --disable-optimize-tests
 ARG SCRIPT_ARG
 COPY scripts/stage_2_test_set1.sh /scripts/
diff --git a/src/ci/docker/host-x86_64/x86_64-gnu-nopt/Dockerfile b/src/ci/docker/host-x86_64/x86_64-gnu-nopt/Dockerfile
index 1b57ae7c8da..854c36ee01c 100644
--- a/src/ci/docker/host-x86_64/x86_64-gnu-nopt/Dockerfile
+++ b/src/ci/docker/host-x86_64/x86_64-gnu-nopt/Dockerfile
@@ -22,12 +22,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
-RUN mkdir -p /config
-RUN echo "[rust]" > /config/nopt-std-config.toml
-RUN echo "optimize = false" >> /config/nopt-std-config.toml
-
 ENV RUST_CONFIGURE_ARGS --build=x86_64-unknown-linux-gnu \
   --disable-optimize-tests \
   --set rust.test-compare-mode
-ENV SCRIPT python3 ../x.py test --stage 1 --config /config/nopt-std-config.toml library/std \
+ENV SCRIPT python3 ../x.py test --stage 1 --set rust.optimize=false library/std \
   && python3 ../x.py --stage 2 test
diff --git a/src/ci/github-actions/jobs.yml b/src/ci/github-actions/jobs.yml
index d6d9e0fb773..217cf764afb 100644
--- a/src/ci/github-actions/jobs.yml
+++ b/src/ci/github-actions/jobs.yml
@@ -300,7 +300,7 @@ auto:
     env:
       IMAGE: i686-gnu-nopt
       DOCKER_SCRIPT: >-
-        python3 ../x.py test --stage 1 --config /config/nopt-std-config.toml library/std &&
+        python3 ../x.py test --stage 1 --set rust.optimize=false library/std &&
         /scripts/stage_2_test_set2.sh
     <<: *job-linux-4c
 
diff --git a/src/tools/miri/src/lib.rs b/src/tools/miri/src/lib.rs
index 68f7d14f57f..e96c81d5b1d 100644
--- a/src/tools/miri/src/lib.rs
+++ b/src/tools/miri/src/lib.rs
@@ -16,7 +16,7 @@
 #![feature(unqualified_local_imports)]
 #![feature(derive_coerce_pointee)]
 #![feature(arbitrary_self_types)]
-#![feature(file_lock)]
+#![cfg_attr(bootstrap, feature(file_lock))]
 // Configure clippy and other lints
 #![allow(
     clippy::collapsible_else_if,
diff --git a/src/tools/miri/tests/pass/shims/fs.rs b/src/tools/miri/tests/pass/shims/fs.rs
index 2f30827c933..9d5725773e6 100644
--- a/src/tools/miri/tests/pass/shims/fs.rs
+++ b/src/tools/miri/tests/pass/shims/fs.rs
@@ -2,7 +2,6 @@
 
 #![feature(io_error_more)]
 #![feature(io_error_uncategorized)]
-#![feature(file_lock)]
 
 use std::collections::BTreeMap;
 use std::ffi::OsString;
diff --git a/src/tools/rust-analyzer/crates/hir-expand/src/inert_attr_macro.rs b/src/tools/rust-analyzer/crates/hir-expand/src/inert_attr_macro.rs
index 543ac0619dd..385c98ef877 100644
--- a/src/tools/rust-analyzer/crates/hir-expand/src/inert_attr_macro.rs
+++ b/src/tools/rust-analyzer/crates/hir-expand/src/inert_attr_macro.rs
@@ -486,7 +486,7 @@ pub const INERT_ATTRIBUTES: &[BuiltinAttribute] = &[
         rustc_legacy_const_generics, Normal, template!(List: "N"), ErrorFollowing,
         INTERNAL_UNSTABLE
     ),
-    // Do not const-check this function's body. It will always get replaced during CTFE.
+    // Do not const-check this function's body. It will always get replaced during CTFE via `hook_special_const_fn`.
     rustc_attr!(
         rustc_do_not_const_check, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE
     ),
diff --git a/tests/ui-fulldeps/stable-mir/check_variant.rs b/tests/ui-fulldeps/stable-mir/check_variant.rs
new file mode 100644
index 00000000000..b0de3369830
--- /dev/null
+++ b/tests/ui-fulldeps/stable-mir/check_variant.rs
@@ -0,0 +1,183 @@
+//@ run-pass
+//! Test that users are able to use stable mir APIs to retrieve
+//! discriminant value and type for AdtDef and Coroutine variants
+
+//@ ignore-stage1
+//@ ignore-cross-compile
+//@ ignore-remote
+//@ edition: 2024
+
+#![feature(rustc_private)]
+#![feature(assert_matches)]
+
+extern crate rustc_middle;
+#[macro_use]
+extern crate rustc_smir;
+extern crate rustc_driver;
+extern crate rustc_interface;
+extern crate stable_mir;
+
+use std::io::Write;
+use std::ops::ControlFlow;
+
+use stable_mir::CrateItem;
+use stable_mir::crate_def::CrateDef;
+use stable_mir::mir::{AggregateKind, Rvalue, Statement, StatementKind};
+use stable_mir::ty::{IntTy, RigidTy, Ty};
+
+const CRATE_NAME: &str = "crate_variant_ty";
+
+/// Test if we can retrieve discriminant info for different types.
+fn test_def_tys() -> ControlFlow<()> {
+    check_adt_mono();
+    check_adt_poly();
+    check_adt_poly2();
+
+    ControlFlow::Continue(())
+}
+
+fn check_adt_mono() {
+    let mono = get_fn("mono").expect_body();
+
+    check_statement_is_aggregate_assign(
+        &mono.blocks[0].statements[0],
+        0,
+        RigidTy::Int(IntTy::Isize),
+    );
+    check_statement_is_aggregate_assign(
+        &mono.blocks[1].statements[0],
+        1,
+        RigidTy::Int(IntTy::Isize),
+    );
+    check_statement_is_aggregate_assign(
+        &mono.blocks[2].statements[0],
+        2,
+        RigidTy::Int(IntTy::Isize),
+    );
+}
+
+fn check_adt_poly() {
+    let poly = get_fn("poly").expect_body();
+
+    check_statement_is_aggregate_assign(
+        &poly.blocks[0].statements[0],
+        0,
+        RigidTy::Int(IntTy::Isize),
+    );
+    check_statement_is_aggregate_assign(
+        &poly.blocks[1].statements[0],
+        1,
+        RigidTy::Int(IntTy::Isize),
+    );
+    check_statement_is_aggregate_assign(
+        &poly.blocks[2].statements[0],
+        2,
+        RigidTy::Int(IntTy::Isize),
+    );
+}
+
+fn check_adt_poly2() {
+    let poly = get_fn("poly2").expect_body();
+
+    check_statement_is_aggregate_assign(
+        &poly.blocks[0].statements[0],
+        0,
+        RigidTy::Int(IntTy::Isize),
+    );
+    check_statement_is_aggregate_assign(
+        &poly.blocks[1].statements[0],
+        1,
+        RigidTy::Int(IntTy::Isize),
+    );
+    check_statement_is_aggregate_assign(
+        &poly.blocks[2].statements[0],
+        2,
+        RigidTy::Int(IntTy::Isize),
+    );
+}
+
+fn get_fn(name: &str) -> CrateItem {
+    stable_mir::all_local_items().into_iter().find(|it| it.name().eq(name)).unwrap()
+}
+
+fn check_statement_is_aggregate_assign(
+    statement: &Statement,
+    expected_discr_val: u128,
+    expected_discr_ty: RigidTy,
+) {
+    if let Statement { kind: StatementKind::Assign(_, rvalue), .. } = statement
+        && let Rvalue::Aggregate(aggregate, _) = rvalue
+        && let AggregateKind::Adt(adt_def, variant_idx, ..) = aggregate
+    {
+        let discr = adt_def.discriminant_for_variant(*variant_idx);
+
+        assert_eq!(discr.val, expected_discr_val);
+        assert_eq!(discr.ty, Ty::from_rigid_kind(expected_discr_ty));
+    } else {
+        unreachable!("Unexpected statement");
+    }
+}
+
+/// This test will generate and analyze a dummy crate using the stable mir.
+/// For that, it will first write the dummy crate into a file.
+/// Then it will create a `StableMir` using custom arguments and then
+/// it will run the compiler.
+fn main() {
+    let path = "defs_ty_input.rs";
+    generate_input(&path).unwrap();
+    let args = &[
+        "rustc".to_string(),
+        "-Cpanic=abort".to_string(),
+        "--crate-name".to_string(),
+        CRATE_NAME.to_string(),
+        path.to_string(),
+    ];
+    run!(args, test_def_tys).unwrap();
+}
+
+fn generate_input(path: &str) -> std::io::Result<()> {
+    let mut file = std::fs::File::create(path)?;
+    write!(
+        file,
+        r#"
+        use std::hint::black_box;
+
+        enum Mono {{
+            A,
+            B(i32),
+            C {{ a: i32, b: u32 }},
+        }}
+
+        enum Poly<T> {{
+            A,
+            B(T),
+            C {{ t: T }},
+        }}
+
+        pub fn main() {{
+            mono();
+            poly();
+            poly2::<i32>(1);
+        }}
+
+        fn mono() {{
+            black_box(Mono::A);
+            black_box(Mono::B(6));
+            black_box(Mono::C {{a: 1, b: 10 }});
+        }}
+
+        fn poly() {{
+            black_box(Poly::<i32>::A);
+            black_box(Poly::B(1i32));
+            black_box(Poly::C {{ t: 1i32 }});
+        }}
+
+        fn poly2<T: Copy>(t: T) {{
+            black_box(Poly::<T>::A);
+            black_box(Poly::B(t));
+            black_box(Poly::C {{ t: t }});
+        }}
+    "#
+    )?;
+    Ok(())
+}