[Clang][Sema] Fix a crash in lambda instantiation

[jcsxky]

Fix #85343
When build lambda expression in lambda instantiation, ThisType is required in Sema::CheckCXXThisCapture to build this capture. Set this type by import Sema::CXXThisScopeRAII and it will be used later in lambda expression transformation.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Qizhi Hu (jcsxky)

Changes

Fix #85343
When build lambda expression in lambda instantiation, ThisType is required in Sema::BuildCaptureInit. Set it in Sema::InstantiateFunctionDefinition when build capture of lambda and it will be used later in lambda expression transformation.

---

Full diff: https://github.com/llvm/llvm-project/pull/85565.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+1)
• (modified) clang/lib/Sema/SemaTemplateInstantiateDecl.cpp (+7)
• (added) clang/test/Sema/PR85343.cpp (+22)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index ba9de1ac98de08..26a87e9ab7b066 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -392,6 +392,7 @@ Bug Fixes to C++ Support
   Fixes (#GH84368).
 - Fixed a crash while checking constraints of a trailing requires-expression of a lambda, that the
   expression references to an entity declared outside of the lambda. (#GH64808)
+- Fix a crash in lambda instantiation that missing set ``ThisType`` when checking capture. Fixes (#GH85343).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index dc972018e7b281..dcfb1798d69641 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -13,12 +13,14 @@
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTMutationListener.h"
+#include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/DeclVisitor.h"
 #include "clang/AST/DependentDiagnostic.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/PrettyDeclStackTrace.h"
+#include "clang/AST/Type.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
@@ -29,6 +31,7 @@
 #include "clang/Sema/SemaInternal.h"
 #include "clang/Sema/Template.h"
 #include "clang/Sema/TemplateInstCallback.h"
+#include "llvm/Support/Casting.h"
 #include "llvm/Support/TimeProfiler.h"
 #include <optional>
 
@@ -5182,6 +5185,10 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
     // Enter the scope of this instantiation. We don't use
     // PushDeclContext because we don't have a scope.
     Sema::ContextRAII savedContext(*this, Function);
+    // We need ThisType in lambda instantiation.
+    Sema::CXXThisScopeRAII ThisScope(
+        *this, dyn_cast<CXXRecordDecl>(Function->getDeclContext()),
+        Qualifiers());
 
     FPFeaturesStateRAII SavedFPFeatures(*this);
     CurFPFeatures = FPOptions(getLangOpts());
diff --git a/clang/test/Sema/PR85343.cpp b/clang/test/Sema/PR85343.cpp
new file mode 100644
index 00000000000000..aa598a5df400bd
--- /dev/null
+++ b/clang/test/Sema/PR85343.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -std=c++11 -verify %s
+// expected-no-diagnostics
+
+template <typename c> auto ab() -> c ;
+
+template <typename> struct e {};
+
+template <typename f> struct ac {
+  template <typename h> static e<decltype(ab<h>()(ab<int>))> i;
+  decltype(i<f>) j;
+};
+
+struct d {
+  template <typename f>
+  d(f) { 
+    ac<f> a;
+  }
+};
+struct a {
+  d b = [=](auto) { (void)[this] {}; };
+};
+void b() { new a; }
\ No newline at end of file

[Sirraide]

Looks fine to me apart from a few minor things.

[jcsxky]

@Sirraide Very thankful for your comments and it really makes the description more clear and easy to be understood! I have updated this patch following your suggestion and please take another look.

[Sirraide]

LGTM except that the comment could still be worded a bit better—especially since I had to take another look at how this here works exactly, but I believe that this is correct: CXXThisScopeRAII does nothing if the context that it is passed is null, and getFunctionLevelDeclContext stops if it finds a CXXRecordDecl, so this should be nonnull iff this lambda is in a class but outside a member function.

[Sirraide]

LGTM

[Sirraide]

CI for the docs seems to be broken because of something clang-format related; the changes to the docs here are trivial, so we should just be able to ignore that.