[lldb] [clang] [clang-tools-extra] [c++20] P1907R1: Support for generalized non-type template arguments of scalar type. (PR #78041)

[Aaron Ballman via cfe-commits]

================
@@ -6472,7 +6494,20 @@ void CXXNameMangler::mangleValueInTemplateArg(QualType 
T, const APValue &V,
       Out << "plcvPcad";
       Kind = Offset;
     } else {
-      if (!V.getLValuePath().empty() || V.isLValueOnePastTheEnd()) {
+      // Clang 11 and before mangled an array subject to array-to-pointer decay
+      // as if it were the declaration itself.
+      bool IsArrayToPointerDecayMangledAsDecl = false;
+      if (TopLevel && Ctx.getLangOpts().getClangABICompat() <=
+                          LangOptions::ClangABI::Ver11) {
+        QualType BType = B.getType();
+        IsArrayToPointerDecayMangledAsDecl =
+            BType->isArrayType() && V.getLValuePath().size() == 1 &&
+            V.getLValuePath()[0].getAsArrayIndex() == 0 &&
+            Ctx.hasSimilarType(T, Ctx.getDecayedType(BType));
+      }
+
----------------
AaronBallman wrote:

I'm surprised by the Clang 11 part: I would have expected this patch to only be 
changing Clang 17 to Clang 18 behavior, right? Should this code be updated for 
Clang 17 instead of Clang 11?

Also, there's no test coverage for these changes.

https://github.com/llvm/llvm-project/pull/78041
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