[flang] Accept interoperable types without BIND(C)

A derived type that meets (most of) the requirements of an interoperable
type but doesn't actually have the BIND(C) attribute can be accepted
as an interoperable type, with optional warnings.

Author: klausler

flang/docs/Extensions.md

@@ -120,6 +120,10 @@ end
   appear in real applications, but are still non-conforming under the
   incomplete tests in F'2023 15.4.3.4.5.
   These cases are compiled with optional portability warnings.
+* `PROCEDURE(), BIND(C) :: PROC` is not conforming, as there is no
+  procedure interface.  This compiler accepts it, since there is otherwise
+  no way to declare an interoperable dummy procedure with an arbitrary
+  interface like `void (*)()`.
 
 ## Extensions, deletions, and legacy features supported by default
 
@@ -351,6 +355,9 @@ end
   when necessary to the type of the result.
   An `OPTIONAL`, `POINTER`, or `ALLOCATABLE` argument after
   the first two cannot be converted, as it may not be present.
+* A derived type that meets (most of) the requirements of an interoperable
+  derived type can be used as such where an interoperable type is
+  required, with warnings, even if it lacks the BIND(C) attribute.
 
 ### Extensions supported when enabled by options
 

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

@@ -48,7 +48,8 @@ ENUM_CLASS(LanguageFeature, BackslashEscapes, OldDebugLines,
     ImpliedDoIndexScope, DistinctCommonSizes, OddIndexVariableRestrictions,
     IndistinguishableSpecifics, SubroutineAndFunctionSpecifics,
     EmptySequenceType, NonSequenceCrayPointee, BranchIntoConstruct,
-    BadBranchTarget, ConvertedArgument, HollerithPolymorphic, ListDirectedSize)
+    BadBranchTarget, ConvertedArgument, HollerithPolymorphic, ListDirectedSize,
+    NonBindCInteroperability)
 
 // Portability and suspicious usage warnings
 ENUM_CLASS(UsageWarning, Portability, PointerToUndefinable,

flang/lib/Semantics/check-declarations.cpp

@@ -115,11 +115,16 @@ class CheckHelper {
     }
     return msg;
   }
+  bool InModuleFile() const {
+    return FindModuleFileContaining(context_.FindScope(messages_.at())) !=
+        nullptr;
+  }
   template <typename... A> parser::Message *WarnIfNotInModuleFile(A &&...x) {
-    if (FindModuleFileContaining(context_.FindScope(messages_.at()))) {
+    if (InModuleFile()) {
       return nullptr;
+    } else {
+      return messages_.Say(std::forward<A>(x)...);
     }
-    return messages_.Say(std::forward<A>(x)...);
   }
   template <typename... A>
   parser::Message *WarnIfNotInModuleFile(parser::CharBlock source, A &&...x) {
@@ -132,6 +137,8 @@ class CheckHelper {
   void CheckGlobalName(const Symbol &);
   void CheckProcedureAssemblyName(const Symbol &symbol);
   void CheckExplicitSave(const Symbol &);
+  parser::Messages WhyNotInteroperableDerivedType(
+      const Symbol &, UnorderedSymbolSet &checked);
   void CheckBindC(const Symbol &);
   void CheckBindCFunctionResult(const Symbol &);
   // Check functions for defined I/O procedures
@@ -2758,11 +2765,117 @@ void CheckHelper::CheckProcedureAssemblyName(const Symbol &symbol) {
   }
 }
 
+parser::Messages CheckHelper::WhyNotInteroperableDerivedType(
+    const Symbol &symbol, UnorderedSymbolSet &checked) {
+  parser::Messages msgs;
+  if (checked.find(symbol) != checked.end()) {
+    return msgs;
+  }
+  checked.insert(symbol);
+  if (const auto *derived{symbol.detailsIf<DerivedTypeDetails>()}) {
+    if (derived->sequence()) { // C1801
+      msgs.Say(symbol.name(),
+          "An interoperable derived type cannot have the SEQUENCE attribute"_err_en_US);
+    } else if (!derived->paramDecls().empty()) { // C1802
+      msgs.Say(symbol.name(),
+          "An interoperable derived type cannot have a type parameter"_err_en_US);
+    } else if (const auto *parent{
+                   symbol.scope()->GetDerivedTypeParent()}) { // C1803
+      if (symbol.attrs().test(Attr::BIND_C)) {
+        msgs.Say(symbol.name(),
+            "A derived type with the BIND attribute cannot be an extended derived type"_err_en_US);
+      } else {
+        bool interoperableParent{true};
+        if (parent->symbol()) {
+          if (auto bad{
+                  WhyNotInteroperableDerivedType(*parent->symbol(), checked)};
+              bad.AnyFatalError()) {
+            auto &msg{msgs.Say(symbol.name(),
+                "The parent of an interoperable type is not interoperable"_err_en_US)};
+            bad.AttachTo(msg, parser::Severity::None);
+            interoperableParent = false;
+          }
+        }
+        if (interoperableParent) {
+          msgs.Say(symbol.name(),
+              "An interoperable type should not be an extended derived type"_warn_en_US);
+        }
+      }
+    }
+    const Symbol *parentComponent{symbol.scope()
+            ? derived->GetParentComponent(*symbol.scope())
+            : nullptr};
+    for (const auto &pair : *symbol.scope()) {
+      const Symbol &component{*pair.second};
+      if (&component == parentComponent) {
+        continue; // was checked above
+      }
+      if (IsProcedure(component)) { // C1804
+        msgs.Say(component.name(),
+            "An interoperable derived type cannot have a type bound procedure"_err_en_US);
+      } else if (IsAllocatableOrPointer(component)) { // C1806
+        msgs.Say(component.name(),
+            "An interoperable derived type cannot have a pointer or allocatable component"_err_en_US);
+      } else if (const auto *type{component.GetType()}) {
+        if (const auto *derived{type->AsDerived()}) {
+          if (auto bad{WhyNotInteroperableDerivedType(
+                  derived->typeSymbol(), checked)};
+              bad.AnyFatalError()) {
+            auto &msg{msgs.Say(component.name(),
+                "Component '%s' of an interoperable derived type must have an interoperable type but does not"_err_en_US,
+                component.name())};
+            bad.AttachTo(msg, parser::Severity::None);
+          } else if (!derived->typeSymbol().GetUltimate().attrs().test(
+                         Attr::BIND_C)) {
+            msgs.Say(component.name(),
+                    "Derived type of component '%s' of an interoperable derived type should have the BIND attribute"_warn_en_US,
+                    component.name())
+                .Attach(derived->typeSymbol().name(),
+                    "Non-BIND(C) component type"_en_US);
+          }
+        } else if (!IsInteroperableIntrinsicType(
+                       *type, context_.languageFeatures())) {
+          auto maybeDyType{evaluate::DynamicType::From(*type)};
+          if (type->category() == DeclTypeSpec::Logical) {
+            if (context_.ShouldWarn(common::UsageWarning::LogicalVsCBool)) {
+              msgs.Say(component.name(),
+                  "A LOGICAL component of an interoperable type should have the interoperable KIND=C_BOOL"_port_en_US);
+            }
+          } else if (type->category() == DeclTypeSpec::Character &&
+              maybeDyType && maybeDyType->kind() == 1) {
+            if (context_.ShouldWarn(common::UsageWarning::BindCCharLength)) {
+              msgs.Say(component.name(),
+                  "A CHARACTER component of an interoperable type should have length 1"_port_en_US);
+            }
+          } else {
+            msgs.Say(component.name(),
+                "Each component of an interoperable derived type must have an interoperable type"_err_en_US);
+          }
+        }
+      }
+      if (auto extents{
+              evaluate::GetConstantExtents(foldingContext_, &component)};
+          extents && evaluate::GetSize(*extents) == 0) {
+        msgs.Say(component.name(),
+            "An array component of an interoperable type must have at least one element"_err_en_US);
+      }
+    }
+    if (derived->componentNames().empty()) { // F'2023 C1805
+      if (context_.ShouldWarn(common::LanguageFeature::EmptyBindCDerivedType)) {
+        msgs.Say(symbol.name(),
+            "A derived type with the BIND attribute should not be empty"_port_en_US);
+      }
+    }
+  }
+  return msgs;
+}
+
 void CheckHelper::CheckBindC(const Symbol &symbol) {
   bool isExplicitBindC{symbol.attrs().test(Attr::BIND_C)};
   if (isExplicitBindC) {
-    CheckConflicting(symbol, Attr::BIND_C, Attr::PARAMETER);
     CheckConflicting(symbol, Attr::BIND_C, Attr::ELEMENTAL);
+    CheckConflicting(symbol, Attr::BIND_C, Attr::INTRINSIC);
+    CheckConflicting(symbol, Attr::BIND_C, Attr::PARAMETER);
   } else {
     // symbol must be interoperable (e.g., dummy argument of interoperable
     // procedure interface) but is not itself BIND(C).
@@ -2832,13 +2945,30 @@ void CheckHelper::CheckBindC(const Symbol &symbol) {
     }
     if (const auto *type{symbol.GetType()}) {
       const auto *derived{type->AsDerived()};
-      if (derived && !derived->typeSymbol().attrs().test(Attr::BIND_C)) {
-        if (auto *msg{messages_.Say(symbol.name(),
-                "The derived type of a BIND(C) object must also be BIND(C)"_err_en_US)}) {
-          msg->Attach(
-              derived->typeSymbol().name(), "Non-interoperable type"_en_US);
+      if (derived) {
+        if (isExplicitBindC) {
+          if (!derived->typeSymbol().attrs().test(Attr::BIND_C)) {
+            if (auto *msg{messages_.Say(symbol.name(),
+                    "The derived type of a BIND(C) object must also be BIND(C)"_err_en_US)}) {
+              msg->Attach(
+                  derived->typeSymbol().name(), "Non-interoperable type"_en_US);
+            }
+            context_.SetError(symbol);
+          }
+        } else {
+          UnorderedSymbolSet checked;
+          if (auto bad{WhyNotInteroperableDerivedType(
+                  derived->typeSymbol(), checked)};
+              !bad.empty()) {
+            if (bad.AnyFatalError()) {
+              if (auto *msg{messages_.Say(symbol.name(),
+                      "The derived type of an interoperable object must be interoperable, but is not"_err_en_US)}) {
+                bad.AttachTo(*msg, parser::Severity::None);
+              }
+              context_.SetError(symbol);
+            }
+          }
         }
-        context_.SetError(symbol);
       }
       if (type->IsAssumedType() || IsAssumedLengthCharacter(symbol)) {
         // ok
@@ -2881,17 +3011,20 @@ void CheckHelper::CheckBindC(const Symbol &symbol) {
           "An interoperable pointer must not be CONTIGUOUS"_err_en_US);
     }
   } else if (const auto *proc{symbol.detailsIf<ProcEntityDetails>()}) {
-    if (!proc->procInterface() ||
-        !proc->procInterface()->attrs().test(Attr::BIND_C)) {
-      if (proc->isDummy()) {
-        messages_.Say(symbol.name(),
-            "A dummy procedure to an interoperable procedure must also be interoperable"_err_en_US);
-        context_.SetError(symbol);
-      } else {
-        messages_.Say(symbol.name(),
-            "An interface name with BIND attribute must be specified if the BIND attribute is specified in a procedure declaration statement"_err_en_US);
-        context_.SetError(symbol);
+    if (!IsBindCProcedure(symbol) && proc->isDummy()) {
+      messages_.Say(symbol.name(),
+          "A dummy procedure to an interoperable procedure must also be interoperable"_err_en_US);
+      context_.SetError(symbol);
+    } else if (!proc->procInterface()) {
+      if (context_.ShouldWarn(
+              common::LanguageFeature::NonBindCInteroperability)) {
+        WarnIfNotInModuleFile(symbol.name(),
+            "An interface name with BIND attribute should be specified if the BIND attribute is specified in a procedure declaration statement"_warn_en_US);
       }
+    } else if (!proc->procInterface()->attrs().test(Attr::BIND_C)) {
+      messages_.Say(symbol.name(),
+          "An interface name with BIND attribute must be specified if the BIND attribute is specified in a procedure declaration statement"_err_en_US);
+      context_.SetError(symbol);
     }
   } else if (const auto *subp{symbol.detailsIf<SubprogramDetails>()}) {
     for (const Symbol *dummy : subp->dummyArgs()) {
@@ -2903,77 +3036,18 @@ void CheckHelper::CheckBindC(const Symbol &symbol) {
         context_.SetError(symbol);
       }
     }
-  } else if (const auto *derived{symbol.detailsIf<DerivedTypeDetails>()}) {
-    if (derived->sequence()) { // C1801
-      messages_.Say(symbol.name(),
-          "A derived type with the BIND attribute cannot have the SEQUENCE attribute"_err_en_US);
-      context_.SetError(symbol);
-    } else if (!derived->paramDecls().empty()) { // C1802
-      messages_.Say(symbol.name(),
-          "A derived type with the BIND attribute has type parameter(s)"_err_en_US);
-      context_.SetError(symbol);
-    } else if (symbol.scope()->GetDerivedTypeParent()) { // C1803
-      messages_.Say(symbol.name(),
-          "A derived type with the BIND attribute cannot extend from another derived type"_err_en_US);
-      context_.SetError(symbol);
-    } else {
-      for (const auto &pair : *symbol.scope()) {
-        const Symbol *component{&*pair.second};
-        if (IsProcedure(*component)) { // C1804
-          messages_.Say(component->name(),
-              "A derived type with the BIND attribute cannot have a type bound procedure"_err_en_US);
-          context_.SetError(symbol);
-        }
-        if (IsAllocatableOrPointer(*component)) { // C1806
-          messages_.Say(component->name(),
-              "A derived type with the BIND attribute cannot have a pointer or allocatable component"_err_en_US);
-          context_.SetError(symbol);
-        }
-        if (const auto *type{component->GetType()}) {
-          if (const auto *derived{type->AsDerived()}) {
-            if (!derived->typeSymbol().attrs().test(Attr::BIND_C)) {
-              if (auto *msg{messages_.Say(component->name(),
-                      "Component '%s' of an interoperable derived type must have the BIND attribute"_err_en_US,
-                      component->name())}) {
-                msg->Attach(derived->typeSymbol().name(),
-                    "Non-interoperable component type"_en_US);
-              }
-              context_.SetError(symbol);
-            }
-          } else if (!IsInteroperableIntrinsicType(
-                         *type, context_.languageFeatures())) {
-            auto maybeDyType{evaluate::DynamicType::From(*type)};
-            if (type->category() == DeclTypeSpec::Logical) {
-              if (context_.ShouldWarn(common::UsageWarning::LogicalVsCBool)) {
-                WarnIfNotInModuleFile(component->name(),
-                    "A LOGICAL component of a BIND(C) type should have the interoperable KIND=C_BOOL"_port_en_US);
-              }
-            } else if (type->category() == DeclTypeSpec::Character &&
-                maybeDyType && maybeDyType->kind() == 1) {
-              if (context_.ShouldWarn(common::UsageWarning::BindCCharLength)) {
-                WarnIfNotInModuleFile(component->name(),
-                    "A CHARACTER component of a BIND(C) type should have length 1"_port_en_US);
-              }
-            } else {
-              messages_.Say(component->name(),
-                  "Each component of an interoperable derived type must have an interoperable type"_err_en_US);
-              context_.SetError(symbol);
-            }
-          }
-        }
-        if (auto extents{
-                evaluate::GetConstantExtents(foldingContext_, component)};
-            extents && evaluate::GetSize(*extents) == 0) {
-          messages_.Say(component->name(),
-              "An array component of an interoperable type must have at least one element"_err_en_US);
-          context_.SetError(symbol);
-        }
+  } else if (symbol.has<DerivedTypeDetails>()) {
+    UnorderedSymbolSet checked;
+    if (auto msgs{WhyNotInteroperableDerivedType(symbol, checked)};
+        !msgs.empty()) {
+      if (msgs.AnyFatalError()) {
+        context_.SetError(symbol);
       }
-    }
-    if (derived->componentNames().empty()) { // F'2023 C1805
-      if (context_.ShouldWarn(common::LanguageFeature::EmptyBindCDerivedType)) {
-        WarnIfNotInModuleFile(symbol.name(),
-            "A derived type with the BIND attribute is empty"_port_en_US);
+      if (msgs.AnyFatalError() ||
+          (!InModuleFile() &&
+              context_.ShouldWarn(
+                  common::LanguageFeature::NonBindCInteroperability))) {
+        context_.messages().Annex(std::move(msgs));
       }
     }
   }

flang/test/Semantics/bind-c03.f90

@@ -1,4 +1,4 @@
-! RUN: %python %S/test_errors.py %s %flang_fc1
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic
 ! Check for C1521
 ! If proc-language-binding-spec (bind(c)) is specified, the proc-interface
 ! shall appear, it shall be an interface-name, and interface-name shall be
@@ -24,7 +24,10 @@ subroutine proc3() bind(c)
   !ERROR: An interface name with BIND attribute must be specified if the BIND attribute is specified in a procedure declaration statement
   procedure(proc2), bind(c) :: pc2
 
-  !ERROR: An interface name with BIND attribute must be specified if the BIND attribute is specified in a procedure declaration statement
+  !WARNING: An interface name with BIND attribute should be specified if the BIND attribute is specified in a procedure declaration statement
   procedure(integer), bind(c) :: pc3
 
+  !WARNING: An interface name with BIND attribute should be specified if the BIND attribute is specified in a procedure declaration statement
+  procedure(), bind(c) :: pc5
+
 end