[clang][Interp] Ignore more non-VarDecl declarations

[tbaeder]

Summary

They are harmless and handled by other means, but we used to return
false from visitDeclStmt.

[aaron.ballman]

clang/lib/AST/Interp/ByteCodeStmtGen.cpp

227

What about other kinds of declarations, such as typedefs or functions?

typedef int foo, bar;
extern int a(), b();

(and so on)

[tbaeder]

clang/lib/AST/Interp/ByteCodeStmtGen.cpp

227

That's a good question, I added these now because I ran into them, but my follow-up question would've indeed been "what others are there?" :)

[aaron.ballman]

clang/lib/AST/Interp/ByteCodeStmtGen.cpp

227

I was going to say: basically anything reachable from this grammar production: http://eel.is/c++draft/dcl.pre#nt:simple-declaration but then I was surprised to see StaticAssertDecl here. It turns out that any declaration at block scope gets wrapped in a DeclStmt. Well, almost any: https://godbolt.org/z/nMYdYTPEq

[aaron.ballman]

LGTM!

clang/lib/AST/Interp/ByteCodeStmtGen.cpp

for (auto *InnerStmt : CompoundStmt->body())
     if (!visitStmt(InnerStmt))
       return false;
   return true;
 }
 
 template <class Emitter>
 bool ByteCodeStmtGen<Emitter>::visitDeclStmt(const DeclStmt *DS) {
   for (auto *D : DS->decls()) {
-    if (isa<StaticAssertDecl>(D))
+    if (isa<StaticAssertDecl, TagDecl, TypedefNameDecl>(D))
       continue;
 
     const auto *VD = dyn_cast<VarDecl>(D);
     if (!VD)
       return false;
     if (!this->visitVarDecl(VD))
       return false;
   }

clang/test/AST/Interp/literals.cpp

namespace TypeTraits {
   };
   struct T {
     ~T() {}
   };
   struct U {};
   static_assert(S3<U>{}.foo(), "");
   static_assert(!S3<T>{}.foo(), "");
 }
+
+#if __cplusplus >= 201402L
+constexpr int ignoredDecls() {
+  static_assert(true, "");
+  struct F { int a; };
+  enum E { b };
+  using A = int;
+  typedef int Z;
+
+  return F{12}.a;
+}
+static_assert(ignoredDecls() == 12, "");
+#endif