[flang] Downgrade a too-strong error message to a warning

[klausler]

When a compilation unit has an interface to an external subroutine or function, and there is a global object (like a module) with the same name, we're emitting an error. This is too strong, the program will still build. This comes up in real applications, too. Downgrade the error to a warning.

[llvmbot]

@llvm/pr-subscribers-flang-semantics

Author: Peter Klausler (klausler)

Changes

When a compilation unit has an interface to an external subroutine or function, and there is a global object (like a module) with the same name, we're emitting an error. This is too strong, the program will still build. This comes up in real applications, too. Downgrade the error to a warning.

---

Full diff: https://github.com/llvm/llvm-project/pull/80095.diff

3 Files Affected:

• (modified) flang/include/flang/Common/Fortran-features.h (+1-1)
• (modified) flang/lib/Semantics/check-declarations.cpp (+5-4)
• (modified) flang/test/Semantics/local-vs-global.f90 (+5-5)

diff --git a/flang/include/flang/Common/Fortran-features.h b/flang/include/flang/Common/Fortran-features.h
index e5757468c0d84..1e678c341d813 100644
--- a/flang/include/flang/Common/Fortran-features.h
+++ b/flang/include/flang/Common/Fortran-features.h
@@ -54,7 +54,7 @@ ENUM_CLASS(UsageWarning, Portability, PointerToUndefinable,
     ShortCharacterActual, ExprPassedToVolatile, ImplicitInterfaceActual,
     PolymorphicTransferArg, PointerComponentTransferArg, TransferSizePresence,
     F202XAllocatableBreakingChange, DimMustBePresent, CommonBlockPadding,
-    LogicalVsCBool, BindCCharLength, ProcDummyArgShapes)
+    LogicalVsCBool, BindCCharLength, ProcDummyArgShapes, ExternalNameConflict)
 
 using LanguageFeatures = EnumSet<LanguageFeature, LanguageFeature_enumSize>;
 using UsageWarnings = EnumSet<UsageWarning, UsageWarning_enumSize>;
diff --git a/flang/lib/Semantics/check-declarations.cpp b/flang/lib/Semantics/check-declarations.cpp
index 8af9dc11f822e..816227fb3354f 100644
--- a/flang/lib/Semantics/check-declarations.cpp
+++ b/flang/lib/Semantics/check-declarations.cpp
@@ -1465,10 +1465,11 @@ void CheckHelper::CheckExternal(const Symbol &symbol) {
       if (interfaceName == definitionName) {
         parser::Message *msg{nullptr};
         if (!IsProcedure(*global)) {
-          if (symbol.flags().test(Symbol::Flag::Function) ||
-              symbol.flags().test(Symbol::Flag::Subroutine)) {
-            msg = messages_.Say(
-                "The global entity '%s' corresponding to the local procedure '%s' is not a callable subprogram"_err_en_US,
+          if ((symbol.flags().test(Symbol::Flag::Function) ||
+                  symbol.flags().test(Symbol::Flag::Subroutine)) &&
+              context_.ShouldWarn(common::UsageWarning::ExternalNameConflict)) {
+            msg = WarnIfNotInModuleFile(
+                "The global entity '%s' corresponding to the local procedure '%s' is not a callable subprogram"_warn_en_US,
                 global->name(), symbol.name());
           }
         } else if (auto chars{Characterize(symbol)}) {
diff --git a/flang/test/Semantics/local-vs-global.f90 b/flang/test/Semantics/local-vs-global.f90
index d1f0a666a6451..6e2b3c47d4552 100644
--- a/flang/test/Semantics/local-vs-global.f90
+++ b/flang/test/Semantics/local-vs-global.f90
@@ -1,4 +1,4 @@
-! RUN: %python %S/test_errors.py %s %flang_fc1
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic
 
 module module_before_1
 end
@@ -46,9 +46,9 @@ function implicit_func_before_2(a)
 
 program test
   external justfine ! OK to name a BLOCK DATA if not called
-  !ERROR: The global entity 'module_before_1' corresponding to the local procedure 'module_before_1' is not a callable subprogram
+  !WARNING: The global entity 'module_before_1' corresponding to the local procedure 'module_before_1' is not a callable subprogram
   external module_before_1
-  !ERROR: The global entity 'block_data_before_1' corresponding to the local procedure 'block_data_before_1' is not a callable subprogram
+  !WARNING: The global entity 'block_data_before_1' corresponding to the local procedure 'block_data_before_1' is not a callable subprogram
   external block_data_before_1
   !ERROR: The global subprogram 'explicit_before_1' may not be referenced via the implicit interface 'explicit_before_1'
   external explicit_before_1
@@ -56,9 +56,9 @@ program test
   !ERROR: The global subprogram 'explicit_func_before_1' may not be referenced via the implicit interface 'explicit_func_before_1'
   external explicit_func_before_1
   external implicit_func_before_1
-  !ERROR: The global entity 'module_after_1' corresponding to the local procedure 'module_after_1' is not a callable subprogram
+  !WARNING: The global entity 'module_after_1' corresponding to the local procedure 'module_after_1' is not a callable subprogram
   external module_after_1
-  !ERROR: The global entity 'block_data_after_1' corresponding to the local procedure 'block_data_after_1' is not a callable subprogram
+  !WARNING: The global entity 'block_data_after_1' corresponding to the local procedure 'block_data_after_1' is not a callable subprogram
   external block_data_after_1
   !ERROR: The global subprogram 'explicit_after_1' may not be referenced via the implicit interface 'explicit_after_1'
   external explicit_after_1

[jeanPerier]

LGTM