llvmbot wrote:

<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang-modules

@llvm/pr-subscribers-clang

Author: Takuto Ikuta (atetubou)

<details>
<summary>Changes</summary>

…system modules

When a template is instantiated from a system module, the location-specific 
diagnostic state (from 'Diag.GetDiagStateForLoc(Loc)') often has 
'SuppressSystemWarnings' set to true because the location itself is within a 
system header defined by the module map.

However, Clang provides mechanisms like 'AllowWarningInSystemHeaders' RAII 
(used for deprecated warnings in 'SemaAvailability.cpp') that temporarily 
override the global suppression state via 
'Diag.setSuppressSystemWarnings(false)'.

Previously, 'DiagnosticIDs::getDiagnosticSeverity' only checked the 
location-specific 'State-&gt;SuppressSystemWarnings', causing it to ignore 
these global overrides when the code originated from a system module.

This patch updates 'getDiagnosticSeverity' to check both the location-specific 
'State-&gt;SuppressSystemWarnings' and the global 
'Diag.getSuppressSystemWarnings()'. This ensures that if the global state has 
been explicitly set to allow warnings (e.g. for deprecated templates 
instantiated in user code), the warning will be emitted even if the template 
definition resides in a system module.

Fixes GH#<!-- -->170429

---
Full diff: https://github.com/llvm/llvm-project/pull/180684.diff


2 Files Affected:

- (modified) clang/lib/Basic/DiagnosticIDs.cpp (+12-5) 
- (added) clang/test/Modules/GH170429.cpp (+30) 


``````````diff
diff --git a/clang/lib/Basic/DiagnosticIDs.cpp 
b/clang/lib/Basic/DiagnosticIDs.cpp
index a1d9d0f34d20d..a5f135083a4d5 100644
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -549,8 +549,14 @@ DiagnosticIDs::getDiagnosticSeverity(unsigned DiagID, 
SourceLocation Loc,
   // If we are in a system header, we ignore it. We look at the diagnostic 
class
   // because we also want to ignore extensions and warnings in -Werror and
   // -pedantic-errors modes, which *map* warnings/extensions to errors.
-  if (State->SuppressSystemWarnings && Loc.isValid() &&
-      SM.isInSystemHeader(SM.getExpansionLoc(Loc))) {
+  //
+  // We check both the location-specific state and the global engine state.
+  // In some cases (like template instantiations from system modules), the
+  // location-specific state might have suppression enabled, but the global
+  // engine state might have an override (e.g. AllowWarningInSystemHeaders)
+  // to show the warning.
+  if (State->SuppressSystemWarnings && Diag.getSuppressSystemWarnings() &&
+      Loc.isValid() && SM.isInSystemHeader(SM.getExpansionLoc(Loc))) {
     bool ShowInSystemHeader = true;
     if (IsCustomDiag)
       ShowInSystemHeader =
@@ -561,9 +567,10 @@ DiagnosticIDs::getDiagnosticSeverity(unsigned DiagID, 
SourceLocation Loc,
     if (!ShowInSystemHeader)
       return diag::Severity::Ignored;
   }
-  // We also ignore warnings due to system macros
-  if (State->SuppressSystemWarnings && Loc.isValid() &&
-      SM.isInSystemMacro(Loc)) {
+  // We also ignore warnings due to system macros. As above, we respect the
+  // global engine suppression state to allow overrides.
+  if (State->SuppressSystemWarnings && Diag.getSuppressSystemWarnings() &&
+      Loc.isValid() && SM.isInSystemMacro(Loc)) {
 
     bool ShowInSystemMacro = true;
     if (const StaticDiagInfoRec *Rec = GetDiagInfo(DiagID))
diff --git a/clang/test/Modules/GH170429.cpp b/clang/test/Modules/GH170429.cpp
new file mode 100644
index 0000000000000..1a982b87c04e2
--- /dev/null
+++ b/clang/test/Modules/GH170429.cpp
@@ -0,0 +1,30 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -fmodules -fmodule-map-file=%t/module.modulemap 
-emit-module -o %t/A.pcm -fmodule-name=A -x c++ %t/module.modulemap
+// RUN: %clang_cc1 -fmodules -fmodule-map-file=%t/module.modulemap 
-fmodule-file=A=%t/A.pcm -I%t %t/use.cc -verify
+
+//--- module.modulemap
+module A [system] {
+  header "A.h"
+}
+
+//--- A.h
+template<typename T>
+void make_unique() {
+  T();
+}
+
+//--- use.cc
+#include "A.h"
+
+// [email protected]:* 2 {{'C' is deprecated}}
+
+class C {
+public:
+  C() __attribute__((deprecated("",""))); // expected-note 2 {{'C' has been 
explicitly marked deprecated here}}
+};
+
+void bar() {
+  make_unique<C>(); // expected-note {{in instantiation of function template 
specialization 'make_unique<C>' requested here}}
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/180684
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