6 files changed, 32 insertions, 13 deletions
diff --git a/compiler/rustc_attr_data_structures/src/version.rs b/compiler/rustc_attr_data_structures/src/version.rs
index 69b0e041d81..030e9520940 100644
--- a/compiler/rustc_attr_data_structures/src/version.rs
+++ b/compiler/rustc_attr_data_structures/src/version.rs
@@ -1,4 +1,5 @@
 use std::fmt::{self, Display};
+use std::sync::OnceLock;
 
 use rustc_macros::{
     Decodable, Encodable, HashStable_Generic, PrintAttribute, current_rustc_version,
@@ -16,8 +17,29 @@ pub struct RustcVersion {
 
 impl RustcVersion {
     pub const CURRENT: Self = current_rustc_version!();
+    pub fn current_overridable() -> Self {
+        *CURRENT_OVERRIDABLE.get_or_init(|| {
+            if let Ok(override_var) = std::env::var("RUSTC_OVERRIDE_VERSION_STRING")
+                && let Some(override_) = Self::parse_str(&override_var)
+            {
+                override_
+            } else {
+                Self::CURRENT
+            }
+        })
+    }
+    fn parse_str(value: &str) -> Option<Self> {
+        // Ignore any suffixes such as "-dev" or "-nightly".
+        let mut components = value.split('-').next().unwrap().splitn(3, '.');
+        let major = components.next()?.parse().ok()?;
+        let minor = components.next()?.parse().ok()?;
+        let patch = components.next().unwrap_or("0").parse().ok()?;
+        Some(RustcVersion { major, minor, patch })
+    }
 }
 
+static CURRENT_OVERRIDABLE: OnceLock<RustcVersion> = OnceLock::new();
+
 impl Display for RustcVersion {
     fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(formatter, "{}.{}.{}", self.major, self.minor, self.patch)
diff --git a/compiler/rustc_attr_parsing/src/attributes/cfg.rs b/compiler/rustc_attr_parsing/src/attributes/cfg.rs
index 7cb1fede174..528f56dfac7 100644
--- a/compiler/rustc_attr_parsing/src/attributes/cfg.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/cfg.rs
@@ -129,9 +129,9 @@ pub fn eval_condition(
 
             // See https://github.com/rust-lang/rust/issues/64796#issuecomment-640851454 for details
             if sess.psess.assume_incomplete_release {
-                RustcVersion::CURRENT > min_version
+                RustcVersion::current_overridable() > min_version
             } else {
-                RustcVersion::CURRENT >= min_version
+                RustcVersion::current_overridable() >= min_version
             }
         }
         MetaItemKind::List(mis) => {
diff --git a/compiler/rustc_hir_typeck/messages.ftl b/compiler/rustc_hir_typeck/messages.ftl
index 23309102c4d..5e79d10612d 100644
--- a/compiler/rustc_hir_typeck/messages.ftl
+++ b/compiler/rustc_hir_typeck/messages.ftl
@@ -169,7 +169,7 @@ hir_typeck_option_result_copied = use `{$def_path}::copied` to copy the value in
 
 hir_typeck_pass_to_variadic_function = can't pass `{$ty}` to variadic function
     .suggestion = cast the value to `{$cast_ty}`
-    .teach_help = certain types, like `{$ty}`, must be casted before passing them to a variadic function, because of arcane ABI rules dictated by the C standard
+    .teach_help = certain types, like `{$ty}`, must be cast before passing them to a variadic function to match the implicit cast that a C compiler would perform as part of C's numeric promotion rules
 
 hir_typeck_ptr_cast_add_auto_to_object = cannot add {$traits_len ->
     [1] auto trait {$traits}
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 342eed751a5..7b71f5de756 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -599,7 +599,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let tcx = self.tcx;
         let rcvr_ty = self.resolve_vars_if_possible(rcvr_ty);
         let mut ty_file = None;
-        let (mut ty_str, short_ty_str) =
+        let (ty_str, short_ty_str) =
             if trait_missing_method && let ty::Dynamic(predicates, _, _) = rcvr_ty.kind() {
                 (predicates.to_string(), with_forced_trimmed_paths!(predicates.to_string()))
             } else {
@@ -738,10 +738,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             err.span_label(within_macro_span, "due to this macro variable");
         }
 
-        if short_ty_str.len() < ty_str.len() && ty_str.len() > 10 {
-            ty_str = short_ty_str;
-        }
-
         if rcvr_ty.references_error() {
             err.downgrade_to_delayed_bug();
         }
diff --git a/compiler/rustc_infer/src/infer/canonical/query_response.rs b/compiler/rustc_infer/src/infer/canonical/query_response.rs
index ec72e05494b..e9cfc96ba50 100644
--- a/compiler/rustc_infer/src/infer/canonical/query_response.rs
+++ b/compiler/rustc_infer/src/infer/canonical/query_response.rs
@@ -23,7 +23,7 @@ use crate::infer::canonical::{
     QueryOutlivesConstraint, QueryRegionConstraints, QueryResponse,
 };
 use crate::infer::region_constraints::{Constraint, RegionConstraintData};
-use crate::infer::{DefineOpaqueTypes, InferCtxt, InferOk, InferResult};
+use crate::infer::{DefineOpaqueTypes, InferCtxt, InferOk, InferResult, SubregionOrigin};
 use crate::traits::query::NoSolution;
 use crate::traits::{
     Obligation, ObligationCause, PredicateObligation, PredicateObligations, ScrubbedTraitError,
@@ -593,10 +593,10 @@ impl<'tcx> InferCtxt<'tcx> {
                     // no action needed
                 }
                 (GenericArgKind::Lifetime(v1), GenericArgKind::Lifetime(v2)) => {
-                    obligations.extend(
-                        self.at(cause, param_env)
-                            .eq(DefineOpaqueTypes::Yes, v1, v2)?
-                            .into_obligations(),
+                    self.inner.borrow_mut().unwrap_region_constraints().make_eqregion(
+                        SubregionOrigin::RelateRegionParamBound(cause.span, None),
+                        v1,
+                        v2,
                     );
                 }
                 (GenericArgKind::Const(v1), GenericArgKind::Const(v2)) => {
diff --git a/compiler/rustc_trait_selection/src/solve/select.rs b/compiler/rustc_trait_selection/src/solve/select.rs
index 1f3168fafb1..21812c8017d 100644
--- a/compiler/rustc_trait_selection/src/solve/select.rs
+++ b/compiler/rustc_trait_selection/src/solve/select.rs
@@ -15,6 +15,7 @@ use crate::solve::inspect::{self, ProofTreeInferCtxtExt};
 
 #[extension(pub trait InferCtxtSelectExt<'tcx>)]
 impl<'tcx> InferCtxt<'tcx> {
+    /// Do not use this directly. This is called from [`crate::traits::SelectionContext::select`].
     fn select_in_new_trait_solver(
         &self,
         obligation: &TraitObligation<'tcx>,