[clang] [Clang] Fixed a crash when instantiating an invalid out-of-line static data member definition in a local class (PR #196772)

[Younan Zhang via cfe-commits]

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@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+template <class T> int f(T) {
+  struct A {
+    static int B; // expected-error {{static data member 'B' not allowed in local struct 'A'}}
+  };
+  int A::B; // expected-note {{previous definition is here}}
+  int A::B = 1; // expected-error {{redefinition of 'B'}}
+  return 0;
+}
+
+int x = f(0);
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zyn0217 wrote:

Did you read my example? I meant, the status quo of whatever D in the instantiator became could be incorrect, and what we need to do is to avoid meaningless instantiation early.

In this case when `A::B` is declared, a name lookup should have happened and that name lookup should find the invalid Decl. And We need to check if we missed a check somewhere that the decl is overlooked and get slipped into the instantiator, and if that's the case, we prevent it. 

https://github.com/llvm/llvm-project/pull/196772