[flang] Submodule names can clash only with submodule names

flang/lib/Semantics/mod-file.cpp

@@ -1183,30 +1183,49 @@ Scope *ModFileReader::Read(const SourceName &name,
   }
   Scope &topScope{isIntrinsic.value_or(false) ? context_.intrinsicModulesScope()
                                               : context_.globalScope()};
-  if (!ancestor) {
+  Symbol *moduleSymbol{nullptr};
+  if (!ancestor) { // module, not submodule
     parentScope = &topScope;
+    auto pair{parentScope->try_emplace(name, UnknownDetails{})};
+    if (!pair.second) {
+      return nullptr;
+    }
+    moduleSymbol = &*pair.first->second;
+    moduleSymbol->set(Symbol::Flag::ModFile);
   } else if (std::optional<SourceName> parent{GetSubmoduleParent(parseTree)}) {
+    // submodule with submodule parent
     parentScope = Read(*parent, false /*not intrinsic*/, ancestor, silent);
   } else {
+    // submodule with module parent
     parentScope = ancestor;
   }
-  auto pair{parentScope->try_emplace(name, UnknownDetails{})};
-  if (!pair.second) {
-    return nullptr;
-  }
   // Process declarations from the module file
-  Symbol &modSymbol{*pair.first->second};
-  modSymbol.set(Symbol::Flag::ModFile);
   bool wasInModuleFile{context_.foldingContext().inModuleFile()};
   context_.foldingContext().set_inModuleFile(true);
   ResolveNames(context_, parseTree, topScope);
   context_.foldingContext().set_inModuleFile(wasInModuleFile);
-  CHECK(modSymbol.has<ModuleDetails>());
-  CHECK(modSymbol.test(Symbol::Flag::ModFile));
-  if (isIntrinsic.value_or(false)) {
-    modSymbol.attrs().set(Attr::INTRINSIC);
+  if (!moduleSymbol) {
+    // Submodule symbols' storage are owned by their parents' scopes,
+    // but their names are not in their parents' dictionaries -- we
+    // don't want to report bogus errors about clashes between submodule
+    // names and other objects in the parent scopes.
+    if (Scope * submoduleScope{ancestor->FindSubmodule(name)}) {
+      moduleSymbol = submoduleScope->symbol();
+      if (moduleSymbol) {
+        moduleSymbol->set(Symbol::Flag::ModFile);
+      }
+    }
+  }
+  if (moduleSymbol) {
+    CHECK(moduleSymbol->has<ModuleDetails>());
+    CHECK(moduleSymbol->test(Symbol::Flag::ModFile));
+    if (isIntrinsic.value_or(false)) {
+      moduleSymbol->attrs().set(Attr::INTRINSIC);
+    }
+    return moduleSymbol->scope();
+  } else {
+    return nullptr;
   }
-  return modSymbol.scope();
 }
 
 parser::Message &ModFileReader::Say(const SourceName &name,

flang/lib/Semantics/resolve-names.cpp

@@ -3230,7 +3230,11 @@ bool ModuleVisitor::BeginSubmodule(
 }
 
 void ModuleVisitor::BeginModule(const parser::Name &name, bool isSubmodule) {
-  auto &symbol{MakeSymbol(name, ModuleDetails{isSubmodule})};
+  // Submodule symbols are not visible in their parents' scopes.
+  Symbol &symbol{isSubmodule ? Resolve(name,
+                                   currScope().MakeSymbol(name.source, Attrs{},
+                                       ModuleDetails{true}))
+                             : MakeSymbol(name, ModuleDetails{false})};
   auto &details{symbol.get<ModuleDetails>()};
   PushScope(Scope::Kind::Module, &symbol);
   details.set_scope(&currScope());

flang/test/Semantics/modproc01.f90

@@ -22,11 +22,12 @@ module subroutine ms(f)
       procedure(mf) :: f
     end subroutine
   end interface
+  integer sm
 end module
 !CHECK:    mf, MODULE, PUBLIC (Function): Subprogram isInterface result:TYPE(pdt2(k2=2_4,l2=n)) res (INTEGER(4) n,CHARACTER(n,1) str,TYPE(pdt1(k1=1_4,l1=n)) x1)
 !CHECK:    pdt1, PUBLIC: DerivedType components: a1
 !CHECK:    pdt2, PUBLIC: DerivedType components: j2,a2
-!CHECK:    sm: Module (m)
+!CHECK:    sm, PUBLIC size=4 offset=0: ObjectEntity type: INTEGER(4)
 !CHECK:    DerivedType scope: pdt1
 !CHECK:      a1, ALLOCATABLE: ObjectEntity type: TYPE(pdt2(int(k1,kind=4),int(l1,kind=4)))
 !CHECK:      k1: TypeParam type:INTEGER(4) Kind
@@ -128,6 +129,7 @@ program test
 !CHECK:    mf, MODULE (Function): Use from mf in m
 !CHECK:    pdt1: Use from pdt1 in m
 !CHECK:    pdt2: Use from pdt2 in m
+!CHECK:    sm: Use from sm in m
 !CHECK:    x size=88 offset=0: ObjectEntity type: TYPE(pdt2(k2=2_4,l2=3_4))
 !CHECK:    DerivedType scope: size=88 alignment=8 instantiation of pdt2(k2=2_4,l2=3_4)
 !CHECK:      a2 size=80 offset=8: ObjectEntity type: TYPE(pdt1(k1=2_4,l1=3_4)) shape: 1_8:2_8

flang/test/Semantics/modproc02.f90

@@ -16,7 +16,6 @@ module subroutine s(x) ! implicitly typed
 
 !CHECK:  Module scope: m size=0 alignment=1 sourceRange=63 bytes
 !CHECK:    s, MODULE, PUBLIC (Subroutine): Subprogram isInterface (REAL(4) x)
-!CHECK:    sm: Module (m)
 !CHECK:    Subprogram scope: s size=4 alignment=4 sourceRange=26 bytes
 !CHECK:      s (Subroutine): HostAssoc
 !CHECK:      x (Implicit) size=4 offset=0: ObjectEntity dummy type: REAL(4)