[clang] [clang] ASTContext: flesh out implementation of getCommonNNS (PR #131964)

[Matheus Izvekov via cfe-commits]

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@@ -13462,13 +13462,114 @@ static ElaboratedTypeKeyword getCommonTypeKeyword(const T *X, const T *Y) {
                                             : ElaboratedTypeKeyword::None;
 }
 
+static NestedNameSpecifier *getCommonNNS(ASTContext &Ctx,
+                                         NestedNameSpecifier *X,
+                                         NestedNameSpecifier *Y, bool IsSame) {
+  if (X == Y)
+    return X;
+
+  NestedNameSpecifier *Canon = Ctx.getCanonicalNestedNameSpecifier(X);
+  if (Canon != Ctx.getCanonicalNestedNameSpecifier(Y)) {
+    assert(!IsSame && "Should be the same NestedNameSpecifier");
+    return nullptr;
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mizvekov wrote:

I would actually prefer to trap here, the original behavior with unreachable, instead of assert is more desirable.

If we get here, we probably have a canonicalization bug somewhere, and in any case we could produce a different type instead of a different sugaring as intended.

https://github.com/llvm/llvm-project/pull/131964