[flang] Fix bogus generic interface error due to hermetic module files

flang/include/flang/Semantics/tools.h

@@ -770,5 +770,7 @@ std::string GetCommonBlockObjectName(const Symbol &, bool underscoring);
 // Check for ambiguous USE associations
 bool HadUseError(SemanticsContext &, SourceName at, const Symbol *);
 
+bool AreSameModuleSymbol(const Symbol &, const Symbol &);
+
 } // namespace Fortran::semantics
 #endif // FORTRAN_SEMANTICS_TOOLS_H_

flang/lib/Semantics/check-declarations.cpp

@@ -2976,14 +2976,6 @@ static std::optional<std::string> DefinesGlobalName(const Symbol &symbol) {
   return std::nullopt;
 }
 
-static bool IsSameSymbolFromHermeticModule(
-    const Symbol &symbol, const Symbol &other) {
-  return symbol.name() == other.name() && symbol.owner().IsModule() &&
-      other.owner().IsModule() && symbol.owner() != other.owner() &&
-      symbol.owner().GetName() &&
-      symbol.owner().GetName() == other.owner().GetName();
-}
-
 // 19.2 p2
 void CheckHelper::CheckGlobalName(const Symbol &symbol) {
   if (auto global{DefinesGlobalName(symbol)}) {
@@ -3001,7 +2993,7 @@ void CheckHelper::CheckGlobalName(const Symbol &symbol) {
           (!IsExternalProcedureDefinition(symbol) ||
               !IsExternalProcedureDefinition(other))) {
         // both are procedures/BLOCK DATA, not both definitions
-      } else if (IsSameSymbolFromHermeticModule(symbol, other)) {
+      } else if (AreSameModuleSymbol(symbol, other)) {
         // Both symbols are the same thing.
       } else if (symbol.has<ModuleDetails>()) {
         Warn(common::LanguageFeature::BenignNameClash, symbol.name(),

flang/lib/Semantics/resolve-names.cpp

@@ -3963,40 +3963,43 @@ void ModuleVisitor::DoAddUse(SourceName location, SourceName localName,
     }
   }
 
+  auto AreSameModuleProcOrBothInterfaces{[](const Symbol &p1,
+                                             const Symbol &p2) {
+    if (IsProcedure(p1) && !IsPointer(p1) && IsProcedure(p2) &&
+        !IsPointer(p2)) {
+      auto classification{ClassifyProcedure(p1)};
+      if (classification == ClassifyProcedure(p2)) {
+        if (classification == ProcedureDefinitionClass::External) {
+          const auto *subp1{p1.detailsIf<SubprogramDetails>()};
+          const auto *subp2{p2.detailsIf<SubprogramDetails>()};
+          return subp1 && subp1->isInterface() && subp2 && subp2->isInterface();
+        } else if (classification == ProcedureDefinitionClass::Module) {
+          return AreSameModuleSymbol(p1, p2);
+        }
+      }
+    }
+    return false;
+  }};
+
   auto AreSameProcedure{[&](const Symbol &p1, const Symbol &p2) {
-    if (&p1 == &p2) {
+    if (&p1.GetUltimate() == &p2.GetUltimate()) {
       return true;
     } else if (p1.name() != p2.name()) {
       return false;
     } else if (p1.attrs().test(Attr::INTRINSIC) ||
         p2.attrs().test(Attr::INTRINSIC)) {
       return p1.attrs().test(Attr::INTRINSIC) &&
           p2.attrs().test(Attr::INTRINSIC);
-    } else if (!IsProcedure(p1) || !IsProcedure(p2)) {
-      return false;
-    } else if (IsPointer(p1) || IsPointer(p2)) {
-      return false;
-    } else if (const auto *subp{p1.detailsIf<SubprogramDetails>()};
-               subp && !subp->isInterface()) {
-      return false; // defined in module, not an external
-    } else if (const auto *subp{p2.detailsIf<SubprogramDetails>()};
-               subp && !subp->isInterface()) {
-      return false; // defined in module, not an external
+    } else if (AreSameModuleProcOrBothInterfaces(p1, p2)) {
+      // Both are external interfaces, perhaps to the same procedure,
+      // or both are module procedures from modules with the same name.
+      auto p1Chars{evaluate::characteristics::Procedure::Characterize(
+          p1, GetFoldingContext())};
+      auto p2Chars{evaluate::characteristics::Procedure::Characterize(
+          p2, GetFoldingContext())};
+      return p1Chars && p2Chars && *p1Chars == *p2Chars;
     } else {
-      // Both are external interfaces, perhaps to the same procedure
-      auto class1{ClassifyProcedure(p1)};
-      auto class2{ClassifyProcedure(p2)};
-      if (class1 == ProcedureDefinitionClass::External &&
-          class2 == ProcedureDefinitionClass::External) {
-        auto chars1{evaluate::characteristics::Procedure::Characterize(
-            p1, GetFoldingContext())};
-        auto chars2{evaluate::characteristics::Procedure::Characterize(
-            p2, GetFoldingContext())};
-        // same procedure interface defined identically in two modules?
-        return chars1 && chars2 && *chars1 == *chars2;
-      } else {
-        return false;
-      }
+      return false;
     }
   }};
 
@@ -4097,13 +4100,32 @@ void ModuleVisitor::DoAddUse(SourceName location, SourceName localName,
       localSymbol = &newSymbol;
     }
     if (useGeneric) {
-      // Combine two use-associated generics
+      // Combine two use-associated generics.
       localSymbol->attrs() =
           useSymbol.attrs() & ~Attrs{Attr::PUBLIC, Attr::PRIVATE};
       localSymbol->flags() = useSymbol.flags();
       AddGenericUse(*localGeneric, localName, useUltimate);
-      localGeneric->clear_derivedType();
-      localGeneric->CopyFrom(*useGeneric);
+      // Don't duplicate specific procedures.
+      std::size_t originalLocalSpecifics{localGeneric->specificProcs().size()};
+      std::size_t useSpecifics{useGeneric->specificProcs().size()};
+      CHECK(originalLocalSpecifics == localGeneric->bindingNames().size());
+      CHECK(useSpecifics == useGeneric->bindingNames().size());
+      std::size_t j{0};
+      for (const Symbol &useSpecific : useGeneric->specificProcs()) {
+        SourceName useBindingName{useGeneric->bindingNames()[j++]};
+        bool isDuplicate{false};
+        std::size_t k{0};
+        for (const Symbol &localSpecific : localGeneric->specificProcs()) {
+          if (localGeneric->bindingNames()[k++] == useBindingName &&
+              AreSameProcedure(localSpecific, useSpecific)) {
+            isDuplicate = true;
+            break;
+          }
+        }
+        if (!isDuplicate) {
+          localGeneric->AddSpecificProc(useSpecific, useBindingName);
+        }
+      }
     }
     localGeneric->clear_derivedType();
     if (combinedDerivedType) {

flang/lib/Semantics/tools.cpp

@@ -1870,4 +1870,9 @@ bool HadUseError(
   }
 }
 
+bool AreSameModuleSymbol(const Symbol &symbol, const Symbol &other) {
+  return symbol.name() == other.name() && symbol.owner().IsModule() &&
+      other.owner().IsModule() && symbol.owner().GetName() &&
+      symbol.owner().GetName() == other.owner().GetName();
+}
 } // namespace Fortran::semantics

flang/test/Semantics/modfile80.F90

@@ -0,0 +1,25 @@
+!RUN: %flang_fc1 -DPART1 %s
+!RUN: %flang_fc1 -DPART2 -fhermetic-module-files %s
+!RUN: %flang_fc1 -DPART3 | FileCheck --allow-empty %s
+!CHECK-NOT: error:
+
+#if defined PART1
+module modfile80a
+  interface generic
+    module procedure specific
+  end interface
+ contains
+  subroutine specific
+  end
+end
+#elif defined PART2
+module modfile80b
+  use modfile80a
+end
+#else
+program test
+  use modfile80a
+  use modfile80b
+  call generic
+end
+#endif