[Clang] suppress deprecated field warnings in implicit special-member functions - #147400

Thank you for submitting a Pull Request (PR) to the LLVM Project!

This PR will be automatically labeled and the relevant teams will be notified.

If you wish to, you can add reviewers by using the "Reviewers" section on this page.

If this is not working for you, it is probably because you do not have write permissions for the repository. In which case you can instead tag reviewers by name in a comment by using @ followed by their GitHub username.

If you have received no comments on your PR for a week, you can request a review by "ping"ing the PR by adding a comment “Ping”. The common courtesy "ping" rate is once a week. Please remember that you are asking for valuable time from other developers.

If you have further questions, they may be answered by the LLVM GitHub User Guide.

You can also ask questions in a comment on this PR, on the LLVM Discord or on the forums.

@llvm/pr-subscribers-clang

Author: Shashi Shankar (shashi1687)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 3c3d29c415249..93b3768c12fb8 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -396,6 +396,30 @@ bool Sema::DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
         if (VD->getTLSKind() != VarDecl::TLS_None)
           targetDiag(*Locs.begin(), diag::err_thread_unsupported);
   }
+  // Suppress deprecation warnings for implicit special-member functions.
+  if (auto *DA = D->getAttr<DeprecatedAttr>()) {
+    if (const FunctionDecl *CurFD = getCurFunctionDecl()) {
+      bool IsImplicitSpecialMember = false;
+
+      // Defaulted constructors.
+      if (auto *CD = dyn_cast<CXXConstructorDecl>(CurFD)) {
+        if (CD->isImplicit() && CD->isDefaulted())
+          IsImplicitSpecialMember = true;
+      }
+
+      // Copy- and move-assignment operators.
+      if (auto *MD = dyn_cast<CXXMethodDecl>(CurFD)) {
+        if ((MD->isCopyAssignmentOperator() ||
+             MD->isMoveAssignmentOperator()) &&
+            MD->isImplicit())
+          IsImplicitSpecialMember = true;
+      }
+
+      if (!IsImplicitSpecialMember) {
+        // Only warn on *explicit* uses.
+        Diag(Locs.front(), diag::warn_deprecated_declarations) << D;
+        Diag(DA->getLocation(), diag::note_deprecated_declarations) << D;
+      }
 
   return false;
 }
diff --git a/clang/test/SemaCXX/deprecated-no-implicit-warning.cpp b/clang/test/SemaCXX/deprecated-no-implicit-warning.cpp
new file mode 100644
index 0000000000000..b830b980d3736
--- /dev/null
+++ b/clang/test/SemaCXX/deprecated-no-implicit-warning.cpp
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -std=c++20 -Wdeprecated-declarations -verify %s
+
+struct A {
+  [[deprecated]] int x = 42;
+};
+
+int main() {
+  A a;        // no-warning
+  A b = a;    // no-warning
+  a = b;      // no-warning
+
+  a.x = b.x;  // expected-warning {{'A::x' is deprecated}}
+  return 0;
+}
+

Hello @zwuis/everyone,

Thank you again for your thorough review. I’ve incorporated all suggestions:

• Moved the suppression guard into the case AR_Deprecated: block
• Used dyn_cast_if_present with a single isImplicit() && isDefaulted() check
• Combined constructor & destructor detection via isa<…>
• Cleaned up the release notes entry

All Sema tests (check-clang) pass locally. Could you please take another look when you have a chance? I really appreciate your time and guidance on this.

Thanks so much! 😊

✅ With the latest revision this PR passed the C/C++ code formatter.

Hi everyone,

I’ve just pushed the final change so the suppression guard now exactly matches what we discussed. Here’s the snippet I added under case AR_Deprecated::

if (auto *MD = dyn_cast_if_present<CXXMethodDecl>(S.getCurFunctionDecl());
    MD && MD->isImplicit() && MD->isDefaulted() &&
    (isa<CXXConstructorDecl, CXXDestructorDecl>(MD) ||
     MD->isCopyAssignmentOperator() ||
     MD->isMoveAssignmentOperator())) {
  return;
}

All local Sema tests (check-clang pass without issues. Could you please take another look when you have a moment? I really appreciate all the feedback so far and want to make sure this meets the project’s standards and let me know if there’s anything else I can improve!

Thank you for your guidance,
Shashi

Hi @cor3ntin ,

Thank you for pointing me toward the simpler isImplicit() check—much cleaner! I’ve updated the patch and added the extra test; everything now builds and check-clang is green.

Whenever you have a moment, could you please give the revision another look? I really appreciate your guidance.

Thanks again!

There is still unaddressed feedback

Thank you so much for your guidance—I really appreciate the clear direction and the time you’ve taken to review my changes. Your feedback has been invaluable!

@shashforge Congratulations on having your first Pull Request (PR) merged into the LLVM Project!

Your changes will be combined with recent changes from other authors, then tested by our build bots. If there is a problem with a build, you may receive a report in an email or a comment on this PR.

Please check whether problems have been caused by your change specifically, as the builds can include changes from many authors. It is not uncommon for your change to be included in a build that fails due to someone else's changes, or infrastructure issues.

How to do this, and the rest of the post-merge process, is covered in detail here.

If your change does cause a problem, it may be reverted, or you can revert it yourself. This is a normal part of LLVM development. You can fix your changes and open a new PR to merge them again.

If you don't get any reports, no action is required from you. Your changes are working as expected, well done!