[flang] Submodule names can clash only with submodule names (#67361)

Name resolution creates symbols for submodules in their parents' scopes.
This can lead to bogus errors about name clashes between submodule names
and other entities in the parents' scopes.

Create symbols for submodules but do not add them to a scope's
dictionary.

4 files changed, 39 insertions, 15 deletions

diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
index cee267a..8684eb1fb 100644
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/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,
diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
index 40f5ab9..b4deac9 100644
--- a/flang/lib/Semantics/resolve-names.cpp
+++ b/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());
diff --git a/flang/test/Semantics/modproc01.f90 b/flang/test/Semantics/modproc01.f90
index c7d0578..5652e15 100644
--- a/flang/test/Semantics/modproc01.f90
+++ b/flang/test/Semantics/modproc01.f90
@@ -22,11 +22,12 @@ module m
       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 @@ end program
 !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
diff --git a/flang/test/Semantics/modproc02.f90 b/flang/test/Semantics/modproc02.f90
index 229ef72..f47f473 100644
--- a/flang/test/Semantics/modproc02.f90
+++ b/flang/test/Semantics/modproc02.f90
@@ -16,7 +16,6 @@ end
 
 !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)