rust-lang · Bryntet · Feb 8, 2026
diff --git a/Cargo.lock b/Cargo.lock
@@ -4392,6 +4392,7 @@ dependencies = [
 name = "rustc_passes"
 version = "0.0.0"
 dependencies = [
+ "rustc-demangle",
  "rustc_abi",
  "rustc_ast",
  "rustc_ast_lowering",
@@ -4407,6 +4408,7 @@ dependencies = [
  "rustc_privacy",
  "rustc_session",
  "rustc_span",
+ "rustc_symbol_mangling",
  "rustc_target",
  "rustc_trait_selection",
  "tracing",

diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
@@ -1232,12 +1232,6 @@ pub(crate) fn start_codegen<'tcx>(
         tcx.ensure_ok().trigger_delayed_bug(def_id);
     }
 
-    // Don't run this test assertions when not doing codegen. Compiletest tries to build
-    // build-fail tests in check mode first and expects it to not give an error in that case.
-    if tcx.sess.opts.output_types.should_codegen() {
-        rustc_symbol_mangling::test::report_symbol_names(tcx);
-    }
-
     // Don't do code generation if there were any errors. Likewise if
     // there were any delayed bugs, because codegen will likely cause
     // more ICEs, obscuring the original problem.

diff --git a/compiler/rustc_passes/Cargo.toml b/compiler/rustc_passes/Cargo.toml
@@ -5,6 +5,7 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
+rustc-demangle = "0.1.27"
 rustc_abi = { path = "../rustc_abi" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_lowering = { path = "../rustc_ast_lowering" }
@@ -20,6 +21,7 @@ rustc_middle = { path = "../rustc_middle" }
 rustc_privacy = { path = "../rustc_privacy" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
+rustc_symbol_mangling = { path = "../rustc_symbol_mangling" }
 rustc_target = { path = "../rustc_target" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
 tracing = "0.1"

diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
@@ -38,7 +38,8 @@ use rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault;
 use rustc_middle::query::Providers;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
-use rustc_middle::ty::{self, TyCtxt, TypingMode};
+use rustc_middle::ty::print::with_no_trimmed_paths;
+use rustc_middle::ty::{self, GenericArgs, TyCtxt, TypingMode};
 use rustc_middle::{bug, span_bug};
 use rustc_session::config::CrateType;
 use rustc_session::lint;
@@ -231,6 +232,12 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     self.check_rustc_must_implement_one_of(*attr_span, fn_names, hir_id,target)
                 },
                 Attribute::Parsed(AttributeKind::DoNotRecommend{attr_span}) => {self.check_do_not_recommend(*attr_span, hir_id, target, item)},
+                Attribute::Parsed(AttributeKind::RustcSymbolName(attr_span)) => {
+                    self.check_rustc_symbol_name(*attr_span, hir_id, target)
+                }
+                Attribute::Parsed(AttributeKind::RustcDefPath(attr_span)) => {
+                    self.check_rustc_def_path(*attr_span, hir_id, target);
+                }
                 Attribute::Parsed(
                     // tidy-alphabetical-start
                     AttributeKind::RustcAllowIncoherentImpl(..)
@@ -300,7 +307,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | AttributeKind::RustcConfusables { .. }
                     | AttributeKind::RustcConstStabilityIndirect
                     | AttributeKind::RustcDeallocator
-                    | AttributeKind::RustcDefPath(..)
                     | AttributeKind::RustcDelayedBugFromInsideQuery
                     | AttributeKind::RustcDenyExplicitImpl(..)
                     | AttributeKind::RustcDummy
@@ -347,7 +353,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | AttributeKind::RustcSkipDuringMethodDispatch { .. }
                     | AttributeKind::RustcSpecializationTrait(..)
                     | AttributeKind::RustcStdInternalSymbol (..)
-                    | AttributeKind::RustcSymbolName(..)
                     | AttributeKind::RustcThenThisWouldNeed(..)
                     | AttributeKind::RustcUnsafeSpecializationMarker(..)
                     | AttributeKind::RustcVariance
@@ -507,6 +512,64 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         self.check_mix_no_mangle_export(hir_id, attrs);
     }
 
+    fn is_valid_symbol_attr(&self, target: &Target) -> bool {
+        self.tcx.sess.opts.output_types.should_codegen()
+            && [
+                Target::Fn,
+                Target::Method(MethodKind::TraitImpl),
+                Target::Method(MethodKind::Inherent),
+                Target::Method(MethodKind::Trait { body: true }),
+                Target::ForeignFn,
+                Target::ForeignStatic,
+                Target::Impl { of_trait: false },
+            ]
+            .contains(target)
+    }
+
+    fn check_rustc_symbol_name(&self, attr_span: Span, hir_id: HirId, target: Target) {
+        use rustc_symbol_mangling::errors::{Kind, TestOutput};
+        let tcx = self.tcx;
+        if !self.is_valid_symbol_attr(&target) {
+            return;
+        }
+        let def_id = hir_id.owner.def_id.to_def_id();
+        let instance = ty::Instance::new_raw(
+            def_id,
+            tcx.erase_and_anonymize_regions(GenericArgs::identity_for_item(tcx, def_id)),
+        );
+        let mangled = tcx.symbol_name(instance);
+        tcx.dcx().emit_err(TestOutput {
+            span: attr_span,
+            kind: Kind::SymbolName,
+            content: format!("{mangled}"),
+        });
+        if let Ok(demangling) = rustc_demangle::try_demangle(mangled.name) {
+            tcx.dcx().emit_err(TestOutput {
+                span: attr_span,
+                kind: Kind::Demangling,
+                content: format!("{demangling}"),
+            });
+            tcx.dcx().emit_err(TestOutput {
+                span: attr_span,
+                kind: Kind::DemanglingAlt,
+                content: format!("{demangling:#}"),
+            });
+        }
+    }
+
+    fn check_rustc_def_path(&self, attr_span: Span, hir_id: HirId, target: Target) {
+        use rustc_symbol_mangling::errors::{Kind, TestOutput};
+        let tcx = self.tcx;
+        if !self.is_valid_symbol_attr(&target) {
+            return;
+        }
+        tcx.dcx().emit_err(TestOutput {
+            span: attr_span,
+            kind: Kind::DefPath,
+            content: with_no_trimmed_paths!(tcx.def_path_str(hir_id.owner.def_id)),
+        });
+    }
+
     fn check_rustc_must_implement_one_of(
         &self,
         attr_span: Span,

diff --git a/compiler/rustc_symbol_mangling/src/lib.rs b/compiler/rustc_symbol_mangling/src/lib.rs
@@ -106,7 +106,6 @@ mod legacy;
 mod v0;
 
 pub mod errors;
-pub mod test;
 
 pub use v0::mangle_internal_symbol;
 

diff --git a/compiler/rustc_symbol_mangling/src/test.rs b/compiler/rustc_symbol_mangling/src/test.rs
diff --git a/tests/ui/symbol-names/impl1.legacy.stderr b/tests/ui/symbol-names/impl1.legacy.stderr
@@ -1,3 +1,27 @@
+error: symbol-name(_ZN209_$LT$$u5b$$RF$dyn$u20$impl1..Foo$u2b$Assoc$u20$$u3d$$u20$extern$u20$$u22$C$u22$$u20$fn$LP$$RF$u8$C$$u20$...$RP$$u2b$impl1..AutoTrait$u3b$$u20$3$u5d$$u20$as$u20$impl1..main..$u7b$$u7b$closure$u7d$$u7d$..Bar$GT$6method17<SYMBOL_HASH>)
+  --> $DIR/impl1.rs:62:13
+   |
+LL |             #[rustc_symbol_name]
+   |             ^^^^^^^^^^^^^^^^^^^^
+
+error: demangling(<[&dyn impl1::Foo+Assoc = extern "C" fn(&u8, ::.)+impl1::AutoTrait; 3] as impl1::main::{{closure}}::Bar>::method::<SYMBOL_HASH>)
+  --> $DIR/impl1.rs:62:13
+   |
+LL |             #[rustc_symbol_name]
+   |             ^^^^^^^^^^^^^^^^^^^^
+
+error: demangling-alt(<[&dyn impl1::Foo+Assoc = extern "C" fn(&u8, ::.)+impl1::AutoTrait; 3] as impl1::main::{{closure}}::Bar>::method)
+  --> $DIR/impl1.rs:62:13
+   |
+LL |             #[rustc_symbol_name]
+   |             ^^^^^^^^^^^^^^^^^^^^
+
+error: def-path(<[&dyn Foo<Assoc = for<'a> extern "C" fn(&'a u8, ...)> + AutoTrait; 3] as main::{closure#1}::Bar>::method)
+  --> $DIR/impl1.rs:69:13
+   |
+LL |             #[rustc_def_path]
+   |             ^^^^^^^^^^^^^^^^^
+
 error: symbol-name(_ZN5impl13foo3Foo3bar17<SYMBOL_HASH>)
   --> $DIR/impl1.rs:14:9
    |
@@ -46,29 +70,5 @@ error: def-path(bar::<impl foo::Foo>::baz)
 LL |         #[rustc_def_path]
    |         ^^^^^^^^^^^^^^^^^
 
-error: symbol-name(_ZN209_$LT$$u5b$$RF$dyn$u20$impl1..Foo$u2b$Assoc$u20$$u3d$$u20$extern$u20$$u22$C$u22$$u20$fn$LP$$RF$u8$C$$u20$...$RP$$u2b$impl1..AutoTrait$u3b$$u20$3$u5d$$u20$as$u20$impl1..main..$u7b$$u7b$closure$u7d$$u7d$..Bar$GT$6method17<SYMBOL_HASH>)
-  --> $DIR/impl1.rs:62:13
-   |
-LL |             #[rustc_symbol_name]
-   |             ^^^^^^^^^^^^^^^^^^^^
-
-error: demangling(<[&dyn impl1::Foo+Assoc = extern "C" fn(&u8, ::.)+impl1::AutoTrait; 3] as impl1::main::{{closure}}::Bar>::method::<SYMBOL_HASH>)
-  --> $DIR/impl1.rs:62:13
-   |
-LL |             #[rustc_symbol_name]
-   |             ^^^^^^^^^^^^^^^^^^^^
-
-error: demangling-alt(<[&dyn impl1::Foo+Assoc = extern "C" fn(&u8, ::.)+impl1::AutoTrait; 3] as impl1::main::{{closure}}::Bar>::method)
-  --> $DIR/impl1.rs:62:13
-   |
-LL |             #[rustc_symbol_name]
-   |             ^^^^^^^^^^^^^^^^^^^^
-
-error: def-path(<[&dyn Foo<Assoc = for<'a> extern "C" fn(&'a u8, ...)> + AutoTrait; 3] as main::{closure#1}::Bar>::method)
-  --> $DIR/impl1.rs:69:13
-   |
-LL |             #[rustc_def_path]
-   |             ^^^^^^^^^^^^^^^^^
-
 error: aborting due to 12 previous errors
 
diff --git a/tests/ui/symbol-names/impl1.v0.stderr b/tests/ui/symbol-names/impl1.v0.stderr
@@ -1,3 +1,27 @@
+error: symbol-name(_RNvXNCNvCsCRATE_HASH_5impl14mains_0ARDNtB<REF>_3Foop5AssocFG_KCRL0_hvEuNtB<REF>_9AutoTraitEL_j3_NtB<REF>_3Bar6method)
+  --> $DIR/impl1.rs:62:13
+   |
+LL |             #[rustc_symbol_name]
+   |             ^^^^^^^^^^^^^^^^^^^^
+
+error: demangling(<[&dyn impl1[d5591eb39db23cbb]::Foo<Assoc = for<'a> extern "C" fn(&'a u8, ...)> + impl1[d5591eb39db23cbb]::AutoTrait; 3usize] as impl1[d5591eb39db23cbb]::main::{closure#1}::Bar>::method)
+  --> $DIR/impl1.rs:62:13
+   |
+LL |             #[rustc_symbol_name]
+   |             ^^^^^^^^^^^^^^^^^^^^
+
+error: demangling-alt(<[&dyn impl1::Foo<Assoc = for<'a> extern "C" fn(&'a u8, ...)> + impl1::AutoTrait; 3] as impl1::main::{closure#1}::Bar>::method)
+  --> $DIR/impl1.rs:62:13
+   |
+LL |             #[rustc_symbol_name]
+   |             ^^^^^^^^^^^^^^^^^^^^
+
+error: def-path(<[&dyn Foo<Assoc = for<'a> extern "C" fn(&'a u8, ...)> + AutoTrait; 3] as main::{closure#1}::Bar>::method)
+  --> $DIR/impl1.rs:69:13
+   |
+LL |             #[rustc_def_path]
+   |             ^^^^^^^^^^^^^^^^^
+
 error: symbol-name(_RNvMNtCsCRATE_HASH_5impl13fooNtB<REF>_3Foo3bar)
   --> $DIR/impl1.rs:14:9
    |
@@ -46,29 +70,5 @@ error: def-path(bar::<impl foo::Foo>::baz)
 LL |         #[rustc_def_path]
    |         ^^^^^^^^^^^^^^^^^
 
-error: symbol-name(_RNvXNCNvCsCRATE_HASH_5impl14mains_0ARDNtB<REF>_3Foop5AssocFG_KCRL0_hvEuNtB<REF>_9AutoTraitEL_j3_NtB<REF>_3Bar6method)
-  --> $DIR/impl1.rs:62:13
-   |
-LL |             #[rustc_symbol_name]
-   |             ^^^^^^^^^^^^^^^^^^^^
-
-error: demangling(<[&dyn impl1[d5591eb39db23cbb]::Foo<Assoc = for<'a> extern "C" fn(&'a u8, ...)> + impl1[d5591eb39db23cbb]::AutoTrait; 3usize] as impl1[d5591eb39db23cbb]::main::{closure#1}::Bar>::method)
-  --> $DIR/impl1.rs:62:13
-   |
-LL |             #[rustc_symbol_name]
-   |             ^^^^^^^^^^^^^^^^^^^^
-
-error: demangling-alt(<[&dyn impl1::Foo<Assoc = for<'a> extern "C" fn(&'a u8, ...)> + impl1::AutoTrait; 3] as impl1::main::{closure#1}::Bar>::method)
-  --> $DIR/impl1.rs:62:13
-   |
-LL |             #[rustc_symbol_name]
-   |             ^^^^^^^^^^^^^^^^^^^^
-
-error: def-path(<[&dyn Foo<Assoc = for<'a> extern "C" fn(&'a u8, ...)> + AutoTrait; 3] as main::{closure#1}::Bar>::method)
-  --> $DIR/impl1.rs:69:13
-   |
-LL |             #[rustc_def_path]
-   |             ^^^^^^^^^^^^^^^^^
-
 error: aborting due to 12 previous errors
-Original file line number
+Diff line change
@@ Expand Up / @@ -106,7 +106,6 @@ mod legacy; @@
     mod v0;
     pub mod errors;
-    pub mod test;
     pub use v0::mangle_internal_symbol;
@@ Expand Down @@