[clang] Fix Name Mangling Crashes

[Mr-Anyone]

It appears that Clang currently mangles names incorrectly when handling lambda expressions in constraint (requires) clauses.

The issue likely stems from mangleLocalName being used, whereas mangleNestedName should be invoked instead. This is supported by the fact that GCC generates the following mangled name for the example below:

template<typename T>
auto a = [](T a) requires requires {
    [](T a){}(a);
} {
    return a;
};

// _ZNK1aIiEUliE_clEiQrqXcltlNS_IT_EUlS2_E_EEfL0p_EE
//                           ^
//                           |
//                         Nested Name
void func() {
    a<int>(1);
}

GCC produces this mangled name:

Example output from clang after this change with previously crashing code:

template<typename T>
auto a = [](T a)requires requires{
    [](T a){}(a);
}{
    return a;
};

//
void func(){
//_ZNK1aIiEMUliE_clEiQrqXclLN1aMUlT_E_clUlS3_E_EEfp_EE
    a<int>(1);
}

void func2() {
// _ZZ5func2vENK3$_0clIiEEDaT_QrqXclLNS_clUlTnivE_EEEE
    [](auto x) requires requires {
        []<int = 0>() {}();
    } {}(0);
}

It seems that something like this resolves these issues:
resolve #132925
resolve #131620
resolve #102169

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[llvmbot]

@llvm/pr-subscribers-clang

Author: Vincent (Mr-Anyone)

Changes

It appears that Clang currently mangles names incorrectly when handling lambda expressions in constraint (requires) clauses.

The issue likely stems from mangleLocalName being used, whereas mangleNestedName should be invoked instead. This is supported by the fact that GCC generates the following mangled name for the example below:

template<typename T>
auto a = [](T a) requires requires {
    [](T a){}(a);
} {
    return a;
};

// _ZNK1aIiEUliE_clEiQrqXcltlNS_IT_EUlS2_E_EEfL0p_EE
//                           ^
//                           |
//                         Nested Name
void func() {
    a<int>(1);
}

GCC produces this mangled name:

Example output from clang after this change with previously crashing code:

template<typename T>
auto a = [](T a)requires requires{
    [](T a){}(a);
}{
    return a;
};

//
void func(){
//_ZNK1aIiEMUliE_clEiQrqXclLN1aMUlT_E_clUlS3_E_EEfp_EE
    a<int>(1);
}

void func2() {
// _ZZ5func2vENK3$_0clIiEEDaT_QrqXclLNS_clUlTnivE_EEEE
    [](auto x) requires requires {
        []<int = 0>() {}();
    } {}(0);
}

It seems that something like this resolves these issues:
resolve #132925
resolve #131620
resolve #102169

---

Full diff: https://github.com/llvm/llvm-project/pull/134486.diff

1 Files Affected:

• (modified) clang/lib/AST/ItaniumMangle.cpp (+10)

diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index fdd84d0bf7c5c..90d6255917654 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -1088,6 +1088,16 @@ void CXXNameMangler::mangleNameWithAbiTags(GlobalDecl GD,
     return;
   }
 
+  const RecordDecl *RD = GetLocalClassDecl(GD.getDecl());
+  if(RD){
+      const DeclContext *DC = Context.getEffectiveDeclContext(RD);
+      const FunctionDecl* FD = dyn_cast<FunctionDecl>(DC);
+      if(FD->getTrailingRequiresClause() && IsLambda){
+          mangleNestedName(GD, DC, AdditionalAbiTags);
+          return;
+      }
+  }
+
   if (isLocalContainerContext(DC)) {
     mangleLocalName(GD, AdditionalAbiTags);
     return;

[zyn0217]

This needs tests as well as release notes.

Also please run clang-format on the changes.

Given that @mizvekov is working on fixing unevaluated lambda contexts, I wonder if these issues could be resolved the other way around, especially since there seems to be a crash on the existing test.

[Mr-Anyone]

It seems that a different approach is needed.