[Clang] Adjust assert from Sema::BuildCXXTypeConstructExpr

[shafik]

Summary

Currently Sema::BuildCXXTypeConstructExpr asserts that list initialization must mean we have an InitListExpr as well. We have several cases of valid code the result in CXXTemporaryObjectExpr in the AST instead for list initialization. Commit 1ae689c seems to indicate that this is not unexpected, although may be a design issue.

This fixes:

https://github.com/llvm/llvm-project/issues/58302
https://github.com/llvm/llvm-project/issues/58753
https://github.com/llvm/llvm-project/issues/59100

[shafik]

The windows failure happened on the build before as well so not related to this change: https://buildkite.com/llvm-project/premerge-checks/builds/123890

[cor3ntin]

clang/lib/Sema/SemaExprCXX.cpp

1464

Exprs.size() == 1 should still be true, right? Is it worth keeping? Maybe?
Similarly, is ListInitialization the right name here? Maybe ParsedAsListInitialization or something? Or a Fixme?

[shafik]

clang/lib/Sema/SemaExprCXX.cpp

1464

I believe ListInitialization is still correct as I mentioned in this bug report: https://github.com/llvm/llvm-project/issues/58302 it is still list initialization.

You have a point it may be worth it to just remove && isa<InitListExpr>(Exprs[0])

[davide]

Exprs.size() == 1 is still valid in every example we've seen, so yes, you might want to keep it (and update the assertion message)

[shafik]

Bring back assert but w/ the check for InitListExpr removed.

[davide]

LGTM with the comment reworded. Thanks.

clang/lib/Sema/SemaExprCXX.cpp

1463

I'd rephrase this as "List initialization must have exactly one expression"

[aaron.ballman]

LGTM with the rewording suggestion applied. Please also add a release note for the fix, thank you!

[shafik]

• Update assert wording
• Add release note

[davide]

LGTM, again.

clang/docs/ReleaseNotes.rst

- GNU attributes being applied prior to standard attributes would be handled
   `Issue 58229 <https://github.com/llvm/llvm-project/issues/58229>`_
 - The builtin type trait ``__is_aggregate`` now returns ``true`` for arrays of incomplete
   types in accordance with the suggested fix for `LWG3823 <https://cplusplus.github.io/LWG/issue3823>`_
 - Fix bug with using enum that could lead to enumerators being treated as if
   they were part of an overload set. This fixes
   `Issue 58067 <https://github.com/llvm/llvm-project/issues/58057>`_
   `Issue 59014 <https://github.com/llvm/llvm-project/issues/59014>`_
   `Issue 54746 <https://github.com/llvm/llvm-project/issues/54746>`_
+- Fix assert that triggers a crash during some types of list initialization that
+  generate a CXXTemporaryObjectExpr instead of a InitListExpr. This fixes
+  `Issue 58302 <https://github.com/llvm/llvm-project/issues/58302>`_
+  `Issue 58753 <https://github.com/llvm/llvm-project/issues/58753>`_
+  `Issue 59100 <https://github.com/llvm/llvm-project/issues/59100>`_
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 - Clang will now check compile-time determinable string literals as format strings.
   Fixes `Issue 55805: <https://github.com/llvm/llvm-project/issues/55805>`_.
 - ``-Wformat`` now recognizes ``%b`` for the ``printf``/``scanf`` family of
   functions and ``%B`` for the ``printf`` family of functions. Fixes
   `Issue 56885: <https://github.com/llvm/llvm-project/issues/56885>`_.

clang/lib/Sema/SemaExprCXX.cpp

 Sema::BuildCXXTypeConstructExpr(TypeSourceInfo *TInfo,
                                 SourceLocation LParenOrBraceLoc,
                                 MultiExprArg Exprs,
                                 SourceLocation RParenOrBraceLoc,
                                 bool ListInitialization) {
   QualType Ty = TInfo->getType();
   SourceLocation TyBeginLoc = TInfo->getTypeLoc().getBeginLoc();
 
-  assert((!ListInitialization ||
-          (Exprs.size() == 1 && isa<InitListExpr>(Exprs[0]))) &&
-         "List initialization must have initializer list as expression.");
+  assert((!ListInitialization || Exprs.size() == 1) &&
+         "List initialization must have exactly one expression.");
   SourceRange FullRange = SourceRange(TyBeginLoc, RParenOrBraceLoc);
 
   InitializedEntity Entity =
       InitializedEntity::InitializeTemporary(Context, TInfo);
   InitializationKind Kind =
       Exprs.size()
           ? ListInitialization
                 ? InitializationKind::CreateDirectList(

clang/test/SemaCXX/cxx0x-initializer-references.cpp

namespace PR20844 {
   struct A {};
   struct B { operator A&(); } b;
   A &a{b}; // expected-error {{excess elements}} expected-note {{in initialization of temporary of type 'A'}}
 }
 
 namespace PR21834 {
 const int &a = (const int &){0}; // expected-error {{cannot bind to an initializer list}}
 }
+
+namespace GH59100 {
+class v {};
+
+template <typename T>
+class V : public v {};
+
+using T = const V<int> &;
+
+template <class D>
+void f() {
+  auto t = T{};
+}
+
+void z()  {
+    f<int>();
+}
+}

clang/test/SemaCXX/cxx2a-consteval.cpp

void f() {
   []() consteval { int i{}; }();
   []() consteval { int i{}; ++i; }();
 }
 void g() {
   (void)[](int i) consteval { return i; }(0);
   (void)[](int i) consteval { return i; }(0);
 }
 }  // namespace GH50455
+
+namespace GH58302 {
+struct A {
+   consteval A(){}
+   consteval operator int() { return 1;}
+};
+
+int f() {
+   int x = A{};
+}
+}