[clang] don't create type source info for vardecl created for structured bindings (#153923)

These are implicit vardecls which its type was never written in source
code. Don't create a TypeLoc and give it a fake source location.

The fake as-written type also didn't match the actual type, which after
fixing this gives some unrelated test churn on a CFG dump, since
statement printing prefers type source info if thats available.

Fixes #153649

This is a regression introduced in
#147835

This regression was never released, so no release notes are added.

Author: mizvekov

clang-tools-extra/test/clang-tidy/checkers/modernize/type-traits-GH153649.cpp

@@ -0,0 +1,15 @@
+// RUN: %check_clang_tidy -std=c++20 %s modernize-type-traits %t
+
+namespace std {
+template <class> struct tuple_size {
+  static const int value = 1;
+};
+template <int, class> struct tuple_element {
+  using type = int;
+};
+}
+
+struct A {};
+template <int> int get(const A&);
+
+auto [a] = A();

clang/lib/Sema/SemaDeclCXX.cpp

@@ -1373,10 +1373,13 @@ static bool checkTupleLikeDecomposition(Sema &S,
         S.BuildReferenceType(T, E.get()->isLValue(), Loc, B->getDeclName());
     if (RefType.isNull())
       return true;
-    auto *RefVD = VarDecl::Create(
-        S.Context, Src->getDeclContext(), Loc, Loc,
-        B->getDeclName().getAsIdentifierInfo(), RefType,
-        S.Context.getTrivialTypeSourceInfo(T, Loc), Src->getStorageClass());
+
+    // Don't give this VarDecl a TypeSourceInfo, since this is a synthesized
+    // entity and this type was never written in source code.
+    auto *RefVD =
+        VarDecl::Create(S.Context, Src->getDeclContext(), Loc, Loc,
+                        B->getDeclName().getAsIdentifierInfo(), RefType,
+                        /*TInfo=*/nullptr, Src->getStorageClass());
     RefVD->setLexicalDeclContext(Src->getLexicalDeclContext());
     RefVD->setTSCSpec(Src->getTSCSpec());
     RefVD->setImplicit();

clang/test/Analysis/anonymous-decls.cpp

@@ -78,12 +78,12 @@ int main() {
 // CHECK-NEXT:   8: decomposition-a-b
 // CHECK-NEXT:   9: [B3.7]([B3.8])
 // CHECK-NEXT:  10: [B3.9]
-// CHECK-NEXT:  11: std::tuple_element<0UL, std::pair<int, int>>::type a = get<0UL>(decomposition-a-b);
+// CHECK-NEXT:  11: std::tuple_element<0UL, std::pair<int, int>>::type &&a = get<0UL>(decomposition-a-b);
 // CHECK-NEXT:  12: get<1UL>
 // CHECK-NEXT:  13: [B3.12] (ImplicitCastExpr, FunctionToPointerDecay, tuple_element<1L, pair<int, int> >::type (*)(pair<int, int> &))
 // CHECK-NEXT:  14: decomposition-a-b
 // CHECK-NEXT:  15: [B3.13]([B3.14])
 // CHECK-NEXT:  16: [B3.15]
-// CHECK-NEXT:  17: std::tuple_element<1UL, std::pair<int, int>>::type b = get<1UL>(decomposition-a-b);
+// CHECK-NEXT:  17: std::tuple_element<1UL, std::pair<int, int>>::type &&b = get<1UL>(decomposition-a-b);
 // CHECK-NEXT:   Preds (1): B1
 // CHECK-NEXT:   Succs (1): B2