[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.

1 files changed, 31 insertions, 12 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,