Auto merge of #116492 - matthiaskrgr:rollup-xzfhmq1, r=matthiaskrgr

Rollup of 7 pull requests

Successful merges:

 - #114564 (Attempt to describe the intent behind the `From` trait further)
 - #116297 (add some docs to hooks/mod.rs)
 - #116423 (Fix typo in attrs.rs)
 - #116466 (`rustc_transmute` cleanups)
 - #116474 (Assorted small cleanups)
 - #116481 (Reuse existing `Some`s in `Option::(x)or`)
 - #116484 (Minor doc clarification in Once::call_once)

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

10 files changed, 69 insertions, 157 deletions

diff --git a/compiler/rustc_attr/src/builtin.rs b/compiler/rustc_attr/src/builtin.rs
index 6f82d6f9323..f013ff45a4f 100644
--- a/compiler/rustc_attr/src/builtin.rs
+++ b/compiler/rustc_attr/src/builtin.rs
@@ -353,28 +353,28 @@ pub fn find_body_stability(
     body_stab
 }
 
+fn insert_or_error(sess: &Session, meta: &MetaItem, item: &mut Option<Symbol>) -> Option<()> {
+    if item.is_some() {
+        handle_errors(
+            &sess.parse_sess,
+            meta.span,
+            AttrError::MultipleItem(pprust::path_to_string(&meta.path)),
+        );
+        None
+    } else if let Some(v) = meta.value_str() {
+        *item = Some(v);
+        Some(())
+    } else {
+        sess.emit_err(session_diagnostics::IncorrectMetaItem { span: meta.span });
+        None
+    }
+}
+
 /// Read the content of a `stable`/`rustc_const_stable` attribute, and return the feature name and
 /// its stability information.
 fn parse_stability(sess: &Session, attr: &Attribute) -> Option<(Symbol, StabilityLevel)> {
     let meta = attr.meta()?;
     let MetaItem { kind: MetaItemKind::List(ref metas), .. } = meta else { return None };
-    let insert_or_error = |meta: &MetaItem, item: &mut Option<Symbol>| {
-        if item.is_some() {
-            handle_errors(
-                &sess.parse_sess,
-                meta.span,
-                AttrError::MultipleItem(pprust::path_to_string(&meta.path)),
-            );
-            return false;
-        }
-        if let Some(v) = meta.value_str() {
-            *item = Some(v);
-            true
-        } else {
-            sess.emit_err(session_diagnostics::IncorrectMetaItem { span: meta.span });
-            false
-        }
-    };
 
     let mut feature = None;
     let mut since = None;
@@ -389,16 +389,8 @@ fn parse_stability(sess: &Session, attr: &Attribute) -> Option<(Symbol, Stabilit
         };
 
         match mi.name_or_empty() {
-            sym::feature => {
-                if !insert_or_error(mi, &mut feature) {
-                    return None;
-                }
-            }
-            sym::since => {
-                if !insert_or_error(mi, &mut since) {
-                    return None;
-                }
-            }
+            sym::feature => insert_or_error(sess, mi, &mut feature)?,
+            sym::since => insert_or_error(sess, mi, &mut since)?,
             _ => {
                 handle_errors(
                     &sess.parse_sess,
@@ -438,23 +430,6 @@ fn parse_stability(sess: &Session, attr: &Attribute) -> Option<(Symbol, Stabilit
 fn parse_unstability(sess: &Session, attr: &Attribute) -> Option<(Symbol, StabilityLevel)> {
     let meta = attr.meta()?;
     let MetaItem { kind: MetaItemKind::List(ref metas), .. } = meta else { return None };
-    let insert_or_error = |meta: &MetaItem, item: &mut Option<Symbol>| {
-        if item.is_some() {
-            handle_errors(
-                &sess.parse_sess,
-                meta.span,
-                AttrError::MultipleItem(pprust::path_to_string(&meta.path)),
-            );
-            return false;
-        }
-        if let Some(v) = meta.value_str() {
-            *item = Some(v);
-            true
-        } else {
-            sess.emit_err(session_diagnostics::IncorrectMetaItem { span: meta.span });
-            false
-        }
-    };
 
     let mut feature = None;
     let mut reason = None;
@@ -473,20 +448,10 @@ fn parse_unstability(sess: &Session, attr: &Attribute) -> Option<(Symbol, Stabil
         };
 
         match mi.name_or_empty() {
-            sym::feature => {
-                if !insert_or_error(mi, &mut feature) {
-                    return None;
-                }
-            }
-            sym::reason => {
-                if !insert_or_error(mi, &mut reason) {
-                    return None;
-                }
-            }
+            sym::feature => insert_or_error(sess, mi, &mut feature)?,
+            sym::reason => insert_or_error(sess, mi, &mut reason)?,
             sym::issue => {
-                if !insert_or_error(mi, &mut issue) {
-                    return None;
-                }
+                insert_or_error(sess, mi, &mut issue)?;
 
                 // These unwraps are safe because `insert_or_error` ensures the meta item
                 // is a name/value pair string literal.
@@ -515,11 +480,7 @@ fn parse_unstability(sess: &Session, attr: &Attribute) -> Option<(Symbol, Stabil
                 }
                 is_soft = true;
             }
-            sym::implied_by => {
-                if !insert_or_error(mi, &mut implied_by) {
-                    return None;
-                }
-            }
+            sym::implied_by => insert_or_error(sess, mi, &mut implied_by)?,
             _ => {
                 handle_errors(
                     &sess.parse_sess,
diff --git a/compiler/rustc_middle/src/hooks/mod.rs b/compiler/rustc_middle/src/hooks/mod.rs
index 12aeae17725..572751d9511 100644
--- a/compiler/rustc_middle/src/hooks/mod.rs
+++ b/compiler/rustc_middle/src/hooks/mod.rs
@@ -1,3 +1,8 @@
+//! "Hooks" provide a way for `tcx` functionality to be provided by some downstream crate without
+//! everything in rustc having to depend on that crate. This is somewhat similar to queries, but
+//! queries come with a lot of machinery for caching and incremental compilation, whereas hooks are
+//! just plain function pointers without any of the query magic.
+
 use crate::mir;
 use crate::query::TyCtxtAt;
 use crate::ty::{Ty, TyCtxt};
diff --git a/compiler/rustc_query_impl/Cargo.toml b/compiler/rustc_query_impl/Cargo.toml
index a44dd5ede2f..a350e8b2e3a 100644
--- a/compiler/rustc_query_impl/Cargo.toml
+++ b/compiler/rustc_query_impl/Cargo.toml
@@ -13,7 +13,6 @@ rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_index = { path = "../rustc_index" }
-rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_query_system = { path = "../rustc_query_system" }
 rustc-rayon-core = { version = "0.5.0", optional = true }
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index d29ab02c1a6..e120f595d92 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -813,7 +813,6 @@ impl Input {
                 FileName::Anon(_) => None,
                 FileName::MacroExpansion(_) => None,
                 FileName::ProcMacroSourceCode(_) => None,
-                FileName::CfgSpec(_) => None,
                 FileName::CliCrateAttr(_) => None,
                 FileName::Custom(_) => None,
                 FileName::DocTest(path, _) => Some(path),
diff --git a/compiler/rustc_smir/Cargo.toml b/compiler/rustc_smir/Cargo.toml
index 4c29f743708..3e0d6baab6a 100644
--- a/compiler/rustc_smir/Cargo.toml
+++ b/compiler/rustc_smir/Cargo.toml
@@ -4,14 +4,13 @@ version = "0.0.0"
 edition = "2021"
 
 [dependencies]
+rustc_driver = { path = "../rustc_driver" }
 rustc_hir = { path = "../rustc_hir" }
+rustc_interface = { path = "../rustc_interface" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
-rustc_driver = { path = "../rustc_driver" }
-rustc_interface = { path = "../rustc_interface" }
-rustc_session = {path = "../rustc_session" }
-tracing = "0.1"
 stable_mir = {path = "../stable_mir" }
+tracing = "0.1"
 
 [features]
diff --git a/compiler/rustc_smir/src/lib.rs b/compiler/rustc_smir/src/lib.rs
index b6c36678db5..d10f46fad9e 100644
--- a/compiler/rustc_smir/src/lib.rs
+++ b/compiler/rustc_smir/src/lib.rs
@@ -10,10 +10,6 @@
     html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
     test(attr(allow(unused_variables), deny(warnings)))
 )]
-#![feature(rustc_private)]
-#![feature(ptr_metadata)]
-#![feature(type_alias_impl_trait)] // Used to define opaque types.
-#![feature(intra_doc_pointers)]
 
 pub mod rustc_internal;
 
diff --git a/compiler/rustc_smir/src/rustc_internal/mod.rs b/compiler/rustc_smir/src/rustc_internal/mod.rs
index 1a9dea99f64..36eb2247253 100644
--- a/compiler/rustc_smir/src/rustc_internal/mod.rs
+++ b/compiler/rustc_smir/src/rustc_internal/mod.rs
@@ -11,7 +11,7 @@ use rustc_driver::{Callbacks, Compilation, RunCompiler};
 use rustc_interface::{interface, Queries};
 use rustc_middle::mir::interpret::AllocId;
 use rustc_middle::ty::TyCtxt;
-pub use rustc_span::def_id::{CrateNum, DefId};
+use rustc_span::def_id::{CrateNum, DefId};
 use rustc_span::Span;
 use stable_mir::CompilerError;
 
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index 36d7c7653ee..6fd61e45fcc 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -280,8 +280,7 @@ impl RealFileName {
 }
 
 /// Differentiates between real files and common virtual files.
-#[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Hash)]
-#[derive(Decodable, Encodable)]
+#[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Hash, Decodable, Encodable)]
 pub enum FileName {
     Real(RealFileName),
     /// Call to `quote!`.
@@ -292,8 +291,6 @@ pub enum FileName {
     // FIXME(jseyfried)
     MacroExpansion(Hash64),
     ProcMacroSourceCode(Hash64),
-    /// Strings provided as `--cfg [cfgspec]` stored in a `crate_cfg`.
-    CfgSpec(Hash64),
     /// Strings provided as crate attributes in the CLI.
     CliCrateAttr(Hash64),
     /// Custom sources for explicit parser calls from plugins and drivers.
@@ -338,7 +335,6 @@ impl fmt::Display for FileNameDisplay<'_> {
             MacroExpansion(_) => write!(fmt, "<macro expansion>"),
             Anon(_) => write!(fmt, "<anon>"),
             ProcMacroSourceCode(_) => write!(fmt, "<proc-macro source code>"),
-            CfgSpec(_) => write!(fmt, "<cfgspec>"),
             CliCrateAttr(_) => write!(fmt, "<crate attribute>"),
             Custom(ref s) => write!(fmt, "<{s}>"),
             DocTest(ref path, _) => write!(fmt, "{}", path.display()),
@@ -364,7 +360,6 @@ impl FileName {
             Anon(_)
             | MacroExpansion(_)
             | ProcMacroSourceCode(_)
-            | CfgSpec(_)
             | CliCrateAttr(_)
             | Custom(_)
             | QuoteExpansion(_)
diff --git a/compiler/rustc_transmute/src/lib.rs b/compiler/rustc_transmute/src/lib.rs
index 6c49e94dc31..4b559632017 100644
--- a/compiler/rustc_transmute/src/lib.rs
+++ b/compiler/rustc_transmute/src/lib.rs
@@ -9,7 +9,7 @@ extern crate tracing;
 pub(crate) use rustc_data_structures::fx::{FxIndexMap as Map, FxIndexSet as Set};
 
 pub mod layout;
-pub(crate) mod maybe_transmutable;
+mod maybe_transmutable;
 
 #[derive(Default)]
 pub struct Assume {
@@ -19,7 +19,7 @@ pub struct Assume {
     pub validity: bool,
 }
 
-/// Either we have an error, transmutation is allowed, or we have an optional
+/// Either transmutation is allowed, we have an error, or we have an optional
 /// Condition that must hold.
 #[derive(Debug, Hash, Eq, PartialEq, Clone)]
 pub enum Answer<R> {
diff --git a/compiler/rustc_transmute/src/maybe_transmutable/mod.rs b/compiler/rustc_transmute/src/maybe_transmutable/mod.rs
index c0141f1f841..bf3c390c800 100644
--- a/compiler/rustc_transmute/src/maybe_transmutable/mod.rs
+++ b/compiler/rustc_transmute/src/maybe_transmutable/mod.rs
@@ -32,26 +32,6 @@ where
     ) -> Self {
         Self { src, dst, scope, assume, context }
     }
-
-    // FIXME(bryangarza): Delete this when all usages are removed
-    pub(crate) fn map_layouts<F, M>(
-        self,
-        f: F,
-    ) -> Result<MaybeTransmutableQuery<M, C>, Answer<<C as QueryContext>::Ref>>
-    where
-        F: FnOnce(
-            L,
-            L,
-            <C as QueryContext>::Scope,
-            &C,
-        ) -> Result<(M, M), Answer<<C as QueryContext>::Ref>>,
-    {
-        let Self { src, dst, scope, assume, context } = self;
-
-        let (src, dst) = f(src, dst, scope, &context)?;
-
-        Ok(MaybeTransmutableQuery { src, dst, scope, assume, context })
-    }
 }
 
 // FIXME: Nix this cfg, so we can write unit tests independently of rustc
@@ -107,42 +87,42 @@ where
     #[instrument(level = "debug", skip(self), fields(src = ?self.src, dst = ?self.dst))]
     pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
         let assume_visibility = self.assume.safety;
-        // FIXME(bryangarza): Refactor this code to get rid of `map_layouts`
-        let query_or_answer = self.map_layouts(|src, dst, scope, context| {
-            // Remove all `Def` nodes from `src`, without checking their visibility.
-            let src = src.prune(&|def| true);
 
-            trace!(?src, "pruned src");
+        let Self { src, dst, scope, assume, context } = self;
 
-            // Remove all `Def` nodes from `dst`, additionally...
-            let dst = if assume_visibility {
-                // ...if visibility is assumed, don't check their visibility.
-                dst.prune(&|def| true)
-            } else {
-                // ...otherwise, prune away all unreachable paths through the `Dst` layout.
-                dst.prune(&|def| context.is_accessible_from(def, scope))
-            };
+        // Remove all `Def` nodes from `src`, without checking their visibility.
+        let src = src.prune(&|def| true);
 
-            trace!(?dst, "pruned dst");
+        trace!(?src, "pruned src");
 
-            // Convert `src` from a tree-based representation to an NFA-based representation.
-            // If the conversion fails because `src` is uninhabited, conclude that the transmutation
-            // is acceptable, because instances of the `src` type do not exist.
-            let src = Nfa::from_tree(src).map_err(|Uninhabited| Answer::Yes)?;
+        // Remove all `Def` nodes from `dst`, additionally...
+        let dst = if assume_visibility {
+            // ...if visibility is assumed, don't check their visibility.
+            dst.prune(&|def| true)
+        } else {
+            // ...otherwise, prune away all unreachable paths through the `Dst` layout.
+            dst.prune(&|def| context.is_accessible_from(def, scope))
+        };
 
-            // Convert `dst` from a tree-based representation to an NFA-based representation.
-            // If the conversion fails because `src` is uninhabited, conclude that the transmutation
-            // is unacceptable, because instances of the `dst` type do not exist.
-            let dst =
-                Nfa::from_tree(dst).map_err(|Uninhabited| Answer::No(Reason::DstIsPrivate))?;
+        trace!(?dst, "pruned dst");
 
-            Ok((src, dst))
-        });
+        // Convert `src` from a tree-based representation to an NFA-based representation.
+        // If the conversion fails because `src` is uninhabited, conclude that the transmutation
+        // is acceptable, because instances of the `src` type do not exist.
+        let src = match Nfa::from_tree(src) {
+            Ok(src) => src,
+            Err(Uninhabited) => return Answer::Yes,
+        };
 
-        match query_or_answer {
-            Ok(query) => query.answer(),
-            Err(answer) => answer,
-        }
+        // Convert `dst` from a tree-based representation to an NFA-based representation.
+        // If the conversion fails because `src` is uninhabited, conclude that the transmutation
+        // is unacceptable, because instances of the `dst` type do not exist.
+        let dst = match Nfa::from_tree(dst) {
+            Ok(dst) => dst,
+            Err(Uninhabited) => return Answer::No(Reason::DstIsPrivate),
+        };
+
+        MaybeTransmutableQuery { src, dst, scope, assume, context }.answer()
     }
 }
 
@@ -156,14 +136,10 @@ where
     #[inline(always)]
     #[instrument(level = "debug", skip(self), fields(src = ?self.src, dst = ?self.dst))]
     pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
-        // FIXME(bryangarza): Refactor this code to get rid of `map_layouts`
-        let query_or_answer = self
-            .map_layouts(|src, dst, scope, context| Ok((Dfa::from_nfa(src), Dfa::from_nfa(dst))));
-
-        match query_or_answer {
-            Ok(query) => query.answer(),
-            Err(answer) => answer,
-        }
+        let Self { src, dst, scope, assume, context } = self;
+        let src = Dfa::from_nfa(src);
+        let dst = Dfa::from_nfa(dst);
+        MaybeTransmutableQuery { src, dst, scope, assume, context }.answer()
     }
 }
 
@@ -171,26 +147,8 @@ impl<C> MaybeTransmutableQuery<Dfa<<C as QueryContext>::Ref>, C>
 where
     C: QueryContext,
 {
-    /// Answers whether a `Nfa` is transmutable into another `Nfa`.
-    ///
-    /// This method converts `src` and `dst` to DFAs, then computes an answer using those DFAs.
+    /// Answers whether a `Dfa` is transmutable into another `Dfa`.
     pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
-        MaybeTransmutableQuery {
-            src: &self.src,
-            dst: &self.dst,
-            scope: self.scope,
-            assume: self.assume,
-            context: self.context,
-        }
-        .answer()
-    }
-}
-
-impl<'l, C> MaybeTransmutableQuery<&'l Dfa<<C as QueryContext>::Ref>, C>
-where
-    C: QueryContext,
-{
-    pub(crate) fn answer(&mut self) -> Answer<<C as QueryContext>::Ref> {
         self.answer_memo(&mut Map::default(), self.src.start, self.dst.start)
     }