[Sema] add cast from IncompleteArrayType to ConstantArrayType in TryReferenceListInitialization (#65918)

Author: HerrCai0907

clang/docs/ReleaseNotes.rst

@@ -264,6 +264,9 @@ Bug Fixes in This Version
   (`#66047 <https://github.com/llvm/llvm-project/issues/66047>`_)
 - Fix parser crash when dealing with ill-formed objective C++ header code. Fixes
   (`#64836 <https://github.com/llvm/llvm-project/issues/64836>`_)
+- Fix crash in implicit conversions from initialize list to arrays of unknown
+  bound for C++20. Fixes
+  (`#62945 <https://github.com/llvm/llvm-project/issues/62945>`_)
 - Clang now allows an ``_Atomic`` qualified integer in a switch statement. Fixes
   (`#65557 <https://github.com/llvm/llvm-project/issues/65557>`_)
 - Fixes crash when trying to obtain the common sugared type of

clang/include/clang/AST/OperationKinds.def

@@ -80,6 +80,7 @@ CAST_OPERATION(LValueToRValue)
 /// (possibly) adding qualifiers or removing noexcept.
 ///   int    -> int
 ///   char** -> const char * const *
+///   int[1] -> int[]
 ///   void () noexcept -> void ()
 CAST_OPERATION(NoOp)
 

clang/lib/Sema/SemaInit.cpp

@@ -18,6 +18,7 @@
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Basic/Specifiers.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Sema/Designator.h"
 #include "clang/Sema/EnterExpressionEvaluationContext.h"
@@ -4528,6 +4529,17 @@ static void TryReferenceListInitialization(Sema &S,
   if (Sequence) {
     if (DestType->isRValueReferenceType() ||
         (T1Quals.hasConst() && !T1Quals.hasVolatile())) {
+      if (S.getLangOpts().CPlusPlus20 &&
+          isa<IncompleteArrayType>(T1->getUnqualifiedDesugaredType()) &&
+          DestType->isRValueReferenceType()) {
+        // C++20 [dcl.init.list]p3.10:
+        // List-initialization of an object or reference of type T is defined as
+        // follows:
+        // ..., unless T is “reference to array of unknown bound of U”, in which
+        // case the type of the prvalue is the type of x in the declaration U
+        // x[] H, where H is the initializer list.
+        Sequence.AddQualificationConversionStep(cv1T1, clang::VK_PRValue);
+      }
       Sequence.AddReferenceBindingStep(cv1T1IgnoreAS,
                                        /*BindingTemporary=*/true);
       if (T1Quals.hasAddressSpace())

clang/test/CodeGenCXX/cxx20-p0388-unbound-ary.cpp

@@ -23,4 +23,13 @@ auto &frob2(int (&arp)[1]) {
 
   return r2;
 }
+
+// CHECK-LABEL: @_ZN3One3fooEi
+// CHECK-NEXT: entry:
+// CHECK-NEXT: ret void
+void foo(int a) {
+  auto f = [](int(&&)[]) {};
+  f({a});
+}
+
 } // namespace One