[clang] b0a7906 - [clang] Fix crash on invalid `std::initializer_list<T>` template-id (#132284)

[via cfe-commits]

Author: offsetof
Date: 2025-04-01T12:44:10+02:00
New Revision: b0a79065178db615b9aaff50337185ad8ee78054

URL: https://github.com/llvm/llvm-project/commit/b0a79065178db615b9aaff50337185ad8ee78054
DIFF: https://github.com/llvm/llvm-project/commit/b0a79065178db615b9aaff50337185ad8ee78054.diff

LOG: [clang] Fix crash on invalid `std::initializer_list<T>` template-id (#132284)

In `Sema::BuildStdInitializerList`, check that the synthesized
template-id `std::initializer_list<T>` is valid (which might not be the
case if the template has associated constraints or subsequent parameters
with default arguments) before forming the type.

Fixes #132256

Added: 
    clang/test/SemaCXX/invalid-std-initializer-list.cpp

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Sema/SemaDeclCXX.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index daad01919ecd4..c034b925cddc6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -371,6 +371,7 @@ Bug Fixes to C++ Support
 - Fixed a Clang regression in C++20 mode where unresolved dependent call expressions were created inside non-dependent contexts (#GH122892)
 - Clang now emits the ``-Wunused-variable`` warning when some structured bindings are unused
   and the ``[[maybe_unused]]`` attribute is not applied. (#GH125810)
+- Fixed a crash caused by invalid declarations of ``std::initializer_list``. (#GH132256)
 - Clang no longer crashes when establishing subsumption between some constraint expressions. (#GH122581)
 - Clang now issues an error when placement new is used to modify a const-qualified variable
   in a ``constexpr`` function. (#GH131432)

diff  --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 676d53a1f4b45..d724e183b69bd 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -12182,10 +12182,14 @@ QualType Sema::BuildStdInitializerList(QualType Element, SourceLocation Loc) {
   Args.addArgument(TemplateArgumentLoc(TemplateArgument(Element),
                                        Context.getTrivialTypeSourceInfo(Element,
                                                                         Loc)));
+
+  QualType T = CheckTemplateIdType(TemplateName(StdInitializerList), Loc, Args);
+  if (T.isNull())
+    return QualType();
+
   return Context.getElaboratedType(
       ElaboratedTypeKeyword::None,
-      NestedNameSpecifier::Create(Context, nullptr, getStdNamespace()),
-      CheckTemplateIdType(TemplateName(StdInitializerList), Loc, Args));
+      NestedNameSpecifier::Create(Context, nullptr, getStdNamespace()), T);
 }
 
 bool Sema::isInitListConstructor(const FunctionDecl *Ctor) {

diff  --git a/clang/test/SemaCXX/invalid-std-initializer-list.cpp b/clang/test/SemaCXX/invalid-std-initializer-list.cpp
new file mode 100644
index 0000000000000..93246b5f03fd4
--- /dev/null
+++ b/clang/test/SemaCXX/invalid-std-initializer-list.cpp
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 %s -verify -std=c++20
+
+namespace std {
+
+template<class T, class = T::x> // expected-error 2 {{type 'int' cannot be used prior to '::' because it has no members}}
+class initializer_list;
+
+}
+
+namespace gh132256 {
+
+auto x = {1}; // expected-note {{in instantiation of default argument for 'initializer_list<int>' required here}}
+
+void f() {
+	for(int x : {1, 2}); // expected-note {{in instantiation of default argument for 'initializer_list<int>' required here}}
+}
+
+}