[clang] 7536ebf - [Clang][SemaCXX] Fix bug where unexpanded lambda captures where assumed to have size 1 (#101385)

[via cfe-commits]

Author: Mital Ashok
Date: 2024-08-05T16:16:55+08:00
New Revision: 7536ebf0ea8e2d09f47ee77e0d60470b5eeb2743

URL: https://github.com/llvm/llvm-project/commit/7536ebf0ea8e2d09f47ee77e0d60470b5eeb2743
DIFF: https://github.com/llvm/llvm-project/commit/7536ebf0ea8e2d09f47ee77e0d60470b5eeb2743.diff

LOG: [Clang][SemaCXX] Fix bug where unexpanded lambda captures where assumed to have size 1 (#101385)

Fixes #63677

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Sema/SemaTemplateInstantiate.cpp
    clang/lib/Sema/TreeTransform.h
    clang/test/SemaCXX/lambda-pack-expansion.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 17696ee9ca484..6f50ab07f1fc0 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -185,6 +185,7 @@ Bug Fixes to C++ Support
 - Clang now correctly recognizes the correct context for parameter
   substitutions in concepts, so it doesn't incorrectly complain of missing
   module imports in those situations. (#GH60336)
+- Fix init-capture packs having a size of one before being instantiated. (#GH63677)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

diff  --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 8995d461362d7..de470739ab78e 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1447,7 +1447,8 @@ namespace {
     }
 
     void transformedLocalDecl(Decl *Old, ArrayRef<Decl *> NewDecls) {
-      if (Old->isParameterPack()) {
+      if (Old->isParameterPack() &&
+          (NewDecls.size() != 1 || !NewDecls.front()->isParameterPack())) {
         SemaRef.CurrentInstantiationScope->MakeInstantiatedLocalArgPack(Old);
         for (auto *New : NewDecls)
           SemaRef.CurrentInstantiationScope->InstantiatedLocalPackArg(

diff  --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 8d3e1edf7a45d..540e1e0cb8df0 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -14340,14 +14340,14 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
               OldVD->getInit()->getSourceRange(), Unexpanded, Expand,
               RetainExpansion, NumExpansions))
         return ExprError();
+      assert(!RetainExpansion && "Should not need to retain expansion after a "
+                                 "capture since it cannot be extended");
       if (Expand) {
         for (unsigned I = 0; I != *NumExpansions; ++I) {
           Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(getSema(), I);
           SubstInitCapture(SourceLocation(), std::nullopt);
         }
-      }
-      if (!Expand || RetainExpansion) {
-        ForgetPartiallySubstitutedPackRAII Forget(getDerived());
+      } else {
         SubstInitCapture(ExpansionTL.getEllipsisLoc(), NumExpansions);
         Result.EllipsisLoc = ExpansionTL.getEllipsisLoc();
       }

diff  --git a/clang/test/SemaCXX/lambda-pack-expansion.cpp b/clang/test/SemaCXX/lambda-pack-expansion.cpp
index 221d1d01a06ae..77b2e244753a9 100644
--- a/clang/test/SemaCXX/lambda-pack-expansion.cpp
+++ b/clang/test/SemaCXX/lambda-pack-expansion.cpp
@@ -41,3 +41,30 @@ int h(Ts... ts) {
 }
 
 }
+
+namespace GH63677 {
+
+template<typename>
+void f() {
+  []<typename... Ts>() -> void {
+    [...us = Ts{}]{
+      (Ts(us), ...);
+    };
+  }.template operator()<int, int>();
+}
+
+template void f<int>();
+
+template <class>
+inline constexpr auto fun =
+  []<class... Ts>(Ts... ts) {
+    return [... us = (Ts&&) ts]<class Fun>(Fun&& fn) mutable {
+      return static_cast<Fun&&>(fn)(static_cast<Ts&&>(us)...);
+    };
+  };
+
+void f() {
+  [[maybe_unused]] auto s = fun<int>(1, 2, 3, 4);
+}
+
+}