[clang][RecoveryExpr] Fix a crash where a dependent type crahes on c-only code path.

[hokein]

Summary

A depenent type is possible in C-only path, add a proper handling when
checking the enum constant.

Fixes https://github.com/llvm/llvm-project/issues/62446

[aaron.ballman]

LGTM, but this should have a release note for the fix. Thanks!

[shafik]

Thank you for the fix, LGTM

[hokein]

add release note.

[hokein]

Thanks for the fast review!

clang/docs/ReleaseNotes.rst

 - A default argument for a non-type template parameter is evaluated and checked
   at the point where it is required. This fixes:
   (`#62224 <https://github.com/llvm/llvm-project/issues/62224>`_) and
   (`#62596 <https://github.com/llvm/llvm-project/issues/62596>`_)
 - Fix an assertion when instantiating the body of a Class Template Specialization
   when it had been instantiated from a partial template specialization with different
   template arguments on the containing class. This fixes:
   (`#60778 <https://github.com/llvm/llvm-project/issues/60778>`_).
+- Fix a crash when an enum constant has a dependent-type recovery expression for
+  C.
+  (`#62446 <https://github.com/llvm/llvm-project/issues/62446>`_).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Bug Fixes to Attribute Support
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed a bug where attribute annotations on type specifiers (enums, classes,
   structs, unions, and scoped enums) were not properly ignored, resulting in

clang/lib/Sema/SemaDecl.cpp

else if (!LastEnumConst) {
         // If we're not in C++, diagnose the overflow of enumerator values,
         // which in C99 means that the enumerator value is not representable in
         // an int (C99 6.7.2.2p2). However, we support GCC's extension that
         // permits enumerator values that are representable in some larger
         // integral type.
         if (!getLangOpts().CPlusPlus && !T.isNull())
           Diag(IdLoc, diag::warn_enum_value_overflow);
       } else if (!getLangOpts().CPlusPlus &&
+                 !EltTy->isDependentType() &&
                  !isRepresentableIntegerValue(Context, EnumVal, EltTy)) {
         // Enforce C99 6.7.2.2p2 even when we compute the next value.
         Diag(IdLoc, diag::ext_enum_value_not_int)
           << toString(EnumVal, 10) << 1;
       }
     }
   }
 

clang/test/AST/ast-dump-recovery.c

void test3() {
   (*__builtin_classify_type)(1);
 
   extern void ext();
   // CHECK:     CallExpr {{.*}} 'void' contains-errors
   // CHECK-NEXT: |-DeclRefExpr {{.*}} 'ext'
   // CHECK-NEXT: `-RecoveryExpr {{.*}} '<dependent type>'
   ext(undef_var);
 }
+
+// Verify no crash.
+void test4() {
+  enum GH62446 {
+    // CHECK:      RecoveryExpr {{.*}} '<dependent type>' contains-errors lvalue
+    // CHECK-NEXT: |-StringLiteral {{.*}} "a"
+    // CHECK-NEXT: `-IntegerLiteral {{.*}} 2
+    invalid_enum_value = "a" * 2,
+    b,
+  };
+}