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

[Matheus Izvekov via cfe-commits]

https://github.com/mizvekov created https://github.com/llvm/llvm-project/pull/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 https://github.com/llvm/llvm-project/issues/153649

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

>From 3c0d0fb4f7d4a14caa3625822018f358198bb28d Mon Sep 17 00:00:00 2001
From: Matheus Izvekov <mizvekov at gmail.com>
Date: Sat, 16 Aug 2025 01:02:25 -0300
Subject: [PATCH] [clang] don't create type source info for vardecl created for
 structured bindings

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 https://github.com/llvm/llvm-project/issues/153649

This regression was never released, so no release notes are added.
---
 .../checkers/modernize/type-traits-GH153649.cpp   | 15 +++++++++++++++
 clang/lib/Sema/SemaDeclCXX.cpp                    |  5 ++++-
 clang/test/Analysis/anonymous-decls.cpp           |  4 ++--
 3 files changed, 21 insertions(+), 3 deletions(-)
 create mode 100644 clang-tools-extra/test/clang-tidy/checkers/modernize/type-traits-GH153649.cpp

diff --git a/clang-tools-extra/test/clang-tidy/checkers/modernize/type-traits-GH153649.cpp b/clang-tools-extra/test/clang-tidy/checkers/modernize/type-traits-GH153649.cpp
new file mode 100644
index 0000000000000..142eb5847ae10
--- /dev/null
+++ b/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();
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index dd66a5f15a970..2ba4f062b61e9 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/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;
+
+    // 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,
-        S.Context.getTrivialTypeSourceInfo(T, Loc), Src->getStorageClass());
+        /*TInfo=*/nullptr, Src->getStorageClass());
     RefVD->setLexicalDeclContext(Src->getLexicalDeclContext());
     RefVD->setTSCSpec(Src->getTSCSpec());
     RefVD->setImplicit();
diff --git a/clang/test/Analysis/anonymous-decls.cpp b/clang/test/Analysis/anonymous-decls.cpp
index 3f972a33aa621..76e5155b61b67 100644
--- a/clang/test/Analysis/anonymous-decls.cpp
+++ b/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