[clang] [Clang] Fix dependent local class instantiation bugs (PR #134038)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 created https://github.com/llvm/llvm-project/pull/134038

Fixes https://github.com/llvm/llvm-project/issues/59734
Fixes https://github.com/llvm/llvm-project/issues/132208


>From a670287721da08e54e2908e9abe52ad86a92769b Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Wed, 2 Apr 2025 14:44:40 +0800
Subject: [PATCH] [Clang] Fix dependent local class instantiation bugs

---
 clang/docs/ReleaseNotes.rst                    |  1 +
 clang/lib/Sema/SemaTemplateInstantiate.cpp     |  3 ++-
 clang/lib/Sema/SemaTemplateInstantiateDecl.cpp | 18 +++++++++++++++++-
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e409f206f6eae..6107fd7667306 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -348,6 +348,7 @@ Bug Fixes to C++ Support
   by template argument deduction.
 - Clang is now better at instantiating the function definition after its use inside
   of a constexpr lambda. (#GH125747)
+- Fixed a local class member function instantiation bug inside dependent lambdas. (#GH59734), (#GH132208)
 - Clang no longer crashes when trying to unify the types of arrays with
   certain differences in qualifiers (this could happen during template argument
   deduction or when building a ternary operator). (#GH97005)
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 00dcadb41e8fb..a46c8c7950710 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -4264,7 +4264,8 @@ Sema::InstantiateClassMembers(SourceLocation PointOfInstantiation,
       if (FunctionDecl *Pattern =
               Function->getInstantiatedFromMemberFunction()) {
 
-        if (Function->isIneligibleOrNotSelected())
+        if (!Instantiation->getDeclContext()->isDependentContext() &&
+            Function->isIneligibleOrNotSelected())
           continue;
 
         if (Function->getTrailingRequiresClause()) {
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 8aaaea0bcdd66..2dc199dc8cbc2 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -5590,7 +5590,6 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
   Function->setLocation(PatternDecl->getLocation());
   Function->setInnerLocStart(PatternDecl->getInnerLocStart());
   Function->setRangeEnd(PatternDecl->getEndLoc());
-  Function->setDeclarationNameLoc(PatternDecl->getNameInfo().getInfo());
 
   EnterExpressionEvaluationContext EvalContext(
       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
@@ -5713,6 +5712,23 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
     MultiLevelTemplateArgumentList TemplateArgs = getTemplateInstantiationArgs(
         Function, DC, /*Final=*/false, Innermost, false, PatternDecl);
 
+    // Let the instantiation use the Pattern's DeclarationNameInfo, due to the
+    // following awkwards:
+    // 1. The function we're instantiating might come from an (implicit)
+    // declaration, while the pattern comes from a definition.
+    // 2. We want the instantiated definition to have a source range pointing to
+    // the definition. Note that we can't set the pattern's DeclarationNameInfo
+    // blindly, as it might contain associated TypeLocs that should have
+    // already been transformed. So we transform the Pattern's DNI for that
+    // purpose. Technically, we should create a new function declaration and
+    // give it everything we want, but InstantiateFunctionDefinition does update
+    // the declaration in place.
+    DeclarationNameInfo DN =
+        SubstDeclarationNameInfo(PatternDecl->getNameInfo(), TemplateArgs);
+    if (!DN.getName())
+      return;
+    Function->setDeclarationNameLoc(DN.getInfo());
+
     // Substitute into the qualifier; we can get a substitution failure here
     // through evil use of alias templates.
     // FIXME: Is CurContext correct for this? Should we go to the (instantiation