Give this diagnostic a diagnostic group

[AaronBallman]

I put this under -Wunitialized because that's the same group it's under in GCC.

Fixes #41104

[llvmbot]

@llvm/pr-subscribers-clang

Author: Aaron Ballman (AaronBallman)

Changes

I put this under -Wunitialized because that's the same group it's under in GCC.

Fixes #41104

---

Full diff: https://github.com/llvm/llvm-project/pull/136182.diff

4 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+4)
• (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+2-1)
• (modified) clang/test/Misc/warning-flags.c (+1-2)
• (added) clang/test/SemaCXX/uninitialized-no-ctor.cpp (+13)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index c75d83a6d1a7a..21f6aba8498b7 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -385,6 +385,10 @@ Improvements to Clang's diagnostics
 
   Fixes #GH131127
 
+- ``-Wuninitialized`` now diagnoses when a class does not declare any
+  constructors to initialize their non-modifiable members. The diagnostic is
+  not new; being controlled via a warning group is what's new. Fixes #GH41104
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 6cbe8b60fe9bf..c29a3422acd26 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2266,7 +2266,8 @@ def err_constructor_byvalue_arg : Error<
   "copy constructor must pass its first argument by reference">;
 def warn_no_constructor_for_refconst : Warning<
   "%select{struct|interface|union|class|enum}0 %1 does not declare any "
-  "constructor to initialize its non-modifiable members">;
+  "constructor to initialize its non-modifiable members">,
+  InGroup<Uninitialized>;
 def note_refconst_member_not_initialized : Note<
   "%select{const|reference}0 member %1 will never be initialized">;
 def ext_ms_explicit_constructor_call : ExtWarn<
diff --git a/clang/test/Misc/warning-flags.c b/clang/test/Misc/warning-flags.c
index 7ac77cc91fdc1..3dc4bb55aa69c 100644
--- a/clang/test/Misc/warning-flags.c
+++ b/clang/test/Misc/warning-flags.c
@@ -18,7 +18,7 @@ This test serves two purposes:
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (57):
+CHECK: Warnings without flags (56):
 
 CHECK-NEXT:   ext_expected_semi_decl_list
 CHECK-NEXT:   ext_missing_whitespace_after_macro_name
@@ -57,7 +57,6 @@ CHECK-NEXT:   warn_method_param_redefinition
 CHECK-NEXT:   warn_missing_case_for_condition
 CHECK-NEXT:   warn_missing_dependent_template_keyword
 CHECK-NEXT:   warn_missing_whitespace_after_macro_name
-CHECK-NEXT:   warn_no_constructor_for_refconst
 CHECK-NEXT:   warn_not_compound_assign
 CHECK-NEXT:   warn_objc_property_copy_missing_on_block
 CHECK-NEXT:   warn_objc_protocol_qualifier_missing_id
diff --git a/clang/test/SemaCXX/uninitialized-no-ctor.cpp b/clang/test/SemaCXX/uninitialized-no-ctor.cpp
new file mode 100644
index 0000000000000..7a08f2f3dc37e
--- /dev/null
+++ b/clang/test/SemaCXX/uninitialized-no-ctor.cpp
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -fsyntax-only -Wuninitialized -verify %s
+// RUN: %clang_cc1 -fsyntax-only -Wno-uninitialized  -verify=good %s
+//good-no-diagnostics
+
+template <class T>
+class RefMem { // expected-warning {{class 'RefMem<int &>' does not declare any constructor to initialize its non-modifiable members}}
+  T &M; // expected-note {{reference member 'M' will never be initialized}}
+};
+
+struct RefRef {
+  RefMem<int &> R; // expected-note {{in instantiation of template class 'RefMem<int &>' requested here}}
+};
+