[flang] Allow a few irrelevant attributes, with warning (#117374)

INTENT, VALUE, and OPTIONAL attributes apply only to dummy arguments. A
couple older compilers accept them, usually with a warning, if they are
applied to names that are not dummy arguments, and they show up in some
older non-portable source code. Change these cases into stern warnings
by default.

Author: klausler

flang/include/flang/Common/Fortran-features.h

@@ -53,7 +53,8 @@ ENUM_CLASS(LanguageFeature, BackslashEscapes, OldDebugLines,
     NonBindCInteroperability, CudaManaged, CudaUnified,
     PolymorphicActualAllocatableOrPointerToMonomorphicDummy, RelaxedPureDummy,
     UndefinableAsynchronousOrVolatileActual, AutomaticInMainProgram, PrintCptr,
-    SavedLocalInSpecExpr, PrintNamelist, AssumedRankPassedToNonAssumedRank)
+    SavedLocalInSpecExpr, PrintNamelist, AssumedRankPassedToNonAssumedRank,
+    IgnoreIrrelevantAttributes)
 
 // Portability and suspicious usage warnings
 ENUM_CLASS(UsageWarning, Portability, PointerToUndefinable,

flang/lib/Common/Fortran-features.cpp

@@ -43,6 +43,7 @@ LanguageFeatureControl::LanguageFeatureControl() {
   warnLanguage_.set(LanguageFeature::BadBranchTarget);
   warnLanguage_.set(LanguageFeature::HollerithPolymorphic);
   warnLanguage_.set(LanguageFeature::ListDirectedSize);
+  warnLanguage_.set(LanguageFeature::IgnoreIrrelevantAttributes);
   warnUsage_.set(UsageWarning::ShortArrayActual);
   warnUsage_.set(UsageWarning::FoldingException);
   warnUsage_.set(UsageWarning::FoldingAvoidsRuntimeCrash);

flang/lib/Semantics/check-declarations.cpp

@@ -320,8 +320,14 @@ void CheckHelper::Check(const Symbol &symbol) {
   if (symbol.attrs().HasAny({Attr::INTENT_IN, Attr::INTENT_INOUT,
           Attr::INTENT_OUT, Attr::OPTIONAL, Attr::VALUE}) &&
       !IsDummy(symbol)) {
-    messages_.Say(
-        "Only a dummy argument may have an INTENT, VALUE, or OPTIONAL attribute"_err_en_US);
+    if (context_.IsEnabled(
+            common::LanguageFeature::IgnoreIrrelevantAttributes)) {
+      context_.Warn(common::LanguageFeature::IgnoreIrrelevantAttributes,
+          "Only a dummy argument should have an INTENT, VALUE, or OPTIONAL attribute"_warn_en_US);
+    } else {
+      messages_.Say(
+          "Only a dummy argument may have an INTENT, VALUE, or OPTIONAL attribute"_err_en_US);
+    }
   } else if (symbol.attrs().test(Attr::VALUE)) {
     CheckValue(symbol, derived);
   }

flang/test/Semantics/call14.f90

@@ -9,7 +9,7 @@ module m
   !ERROR: VALUE attribute may apply only to a dummy data object
   subroutine C863(notData,assumedSize,coarray,coarrayComponent,assumedRank,assumedLen)
     external :: notData
-    !ERROR: Only a dummy argument may have an INTENT, VALUE, or OPTIONAL attribute
+    !WARNING: Only a dummy argument should have an INTENT, VALUE, or OPTIONAL attribute
     real, value :: notADummy
     value :: notData
     !ERROR: VALUE attribute may not apply to an assumed-size array

flang/test/Semantics/resolve58.f90

@@ -69,12 +69,12 @@ subroutine s6()
 
   !ERROR: Implied-shape array 'local1' must be a named constant or a dummy argument
   real, dimension (*) :: local1
-  !ERROR: Only a dummy argument may have an INTENT, VALUE, or OPTIONAL attribute
+  !WARNING: Only a dummy argument should have an INTENT, VALUE, or OPTIONAL attribute
   real, intent(in) :: local2
-  !ERROR: Only a dummy argument may have an INTENT, VALUE, or OPTIONAL attribute
+  !WARNING: Only a dummy argument should have an INTENT, VALUE, or OPTIONAL attribute
   procedure(), intent(in) :: p1
-  !ERROR: Only a dummy argument may have an INTENT, VALUE, or OPTIONAL attribute
+  !WARNING: Only a dummy argument should have an INTENT, VALUE, or OPTIONAL attribute
   real, optional :: local3
-  !ERROR: Only a dummy argument may have an INTENT, VALUE, or OPTIONAL attribute
+  !WARNING: Only a dummy argument should have an INTENT, VALUE, or OPTIONAL attribute
   procedure(), optional :: p2
 end subroutine