Author: Haojian Wu
Date: 2025-12-31T14:52:10+01:00
New Revision: 5c2a8117ac12c455d69df61dd6a2f5f3fa07f964

URL: 
https://github.com/llvm/llvm-project/commit/5c2a8117ac12c455d69df61dd6a2f5f3fa07f964
DIFF: 
https://github.com/llvm/llvm-project/commit/5c2a8117ac12c455d69df61dd6a2f5f3fa07f964.diff

LOG: [clang] Preserve the initializer when variable declaration deduction fails 
(#173546)

Fix https://github.com/clangd/clangd/issues/2572.

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Sema/SemaDecl.cpp
    clang/test/AST/ast-dump-recovery.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 2319ff13f7864..ecdbbc05cdef4 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -875,6 +875,7 @@ Improvements
   including diagnosing when the array-section's base is not a named-variable.
 - Handling of ``use_device_addr`` and ``use_device_ptr`` in the presence of
   other maps with the same base-pointer/variable, was improved.
+- Preserve the initializer when variable declaration dedution fails for better 
error recovery.
 
 Additional Information
 ======================

diff  --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 11323803e1910..f636e8e35a3d5 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -13840,8 +13840,15 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr 
*Init, bool DirectInit) {
       return;
     }
 
-    if (DeduceVariableDeclarationType(VDecl, DirectInit, Init))
+    if (DeduceVariableDeclarationType(VDecl, DirectInit, Init)) {
+      assert(VDecl->isInvalidDecl() &&
+             "decl should be invalidated when deduce fails");
+      if (auto *RecoveryExpr =
+              CreateRecoveryExpr(Init->getBeginLoc(), Init->getEndLoc(), 
{Init})
+                  .get())
+        VDecl->setInit(RecoveryExpr);
       return;
+    }
   }
 
   this->CheckAttributesOnDeducedType(RealDecl);

diff  --git a/clang/test/AST/ast-dump-recovery.cpp 
b/clang/test/AST/ast-dump-recovery.cpp
index 060ae3b62b6f8..80ec0a449d556 100644
--- a/clang/test/AST/ast-dump-recovery.cpp
+++ b/clang/test/AST/ast-dump-recovery.cpp
@@ -301,3 +301,11 @@ void foo() {
   U g{};
 }
 } // namespace GH112560
+
+// CHECK:     VarDecl {{.*}} invalid x 'auto *' cinit
+// CHECK-NEXT: `-RecoveryExpr {{.*}} '<dependent type>' contains-errors lvalue
+// CHECK-NEXT:   `-CallExpr {{.*}} 'int'
+// DISABLED-NOT: -RecoveryExpr {{.*}} contains-errors
+void brokenDeducedVarDecl() {
+   auto* x = some_func(nullptr);
+}


        
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