[flang] Fix edge case in USE-associated generics

It is generally an error when a USE-associated name clashes
with a name defined locally, but not in all cases; a generic
interface can be both USE-associated and locally defined.
This works, but not when there is also a local subprogram
with the same name, which is valid when that subprogram is
a specific of the local generic.  A bogus error issues at
the point of the USE because name resolution will have already
defined a symbol for the local subprogram.

The solution is to collect the names of local generics when
creating the program tree, and then create their symbols as
well if their names are also local subprograms, prior to any
USE association processing.

Differential Revision: https://reviews.llvm.org/D119566

1 files changed, 37 insertions, 0 deletions

diff --git a/flang/lib/Semantics/program-tree.cpp b/flang/lib/Semantics/program-tree.cpp
index e20299b..9d76cfa 100644
--- a/flang/lib/Semantics/program-tree.cpp
+++ b/flang/lib/Semantics/program-tree.cpp
@@ -44,6 +44,37 @@ static void GetEntryStmts(
   }
 }
 
+// Collects generics that define simple names that could include
+// identically-named subprograms as specific procedures.
+static void GetGenerics(
+    ProgramTree &node, const parser::SpecificationPart &spec) {
+  for (const auto &decl :
+      std::get<std::list<parser::DeclarationConstruct>>(spec.t)) {
+    if (const auto *spec{
+            std::get_if<parser::SpecificationConstruct>(&decl.u)}) {
+      if (const auto *generic{std::get_if<
+              parser::Statement<common::Indirection<parser::GenericStmt>>>(
+              &spec->u)}) {
+        const parser::GenericStmt &genericStmt{generic->statement.value()};
+        const auto &genericSpec{std::get<parser::GenericSpec>(genericStmt.t)};
+        node.AddGeneric(genericSpec);
+      } else if (const auto *interface{
+                     std::get_if<common::Indirection<parser::InterfaceBlock>>(
+                         &spec->u)}) {
+        const parser::InterfaceBlock &interfaceBlock{interface->value()};
+        const parser::InterfaceStmt &interfaceStmt{
+            std::get<parser::Statement<parser::InterfaceStmt>>(interfaceBlock.t)
+                .statement};
+        const auto *genericSpec{
+            std::get_if<std::optional<parser::GenericSpec>>(&interfaceStmt.u)};
+        if (genericSpec && genericSpec->has_value()) {
+          node.AddGeneric(**genericSpec);
+        }
+      }
+    }
+  }
+}
+
 template <typename T>
 static ProgramTree BuildSubprogramTree(const parser::Name &name, const T &x) {
   const auto &spec{std::get<parser::SpecificationPart>(x.t)};
@@ -53,6 +84,7 @@ static ProgramTree BuildSubprogramTree(const parser::Name &name, const T &x) {
   ProgramTree node{name, spec, &exec};
   GetEntryStmts(node, spec);
   GetEntryStmts(node, exec);
+  GetGenerics(node, spec);
   if (subps) {
     for (const auto &subp :
         std::get<std::list<parser::InternalSubprogram>>(subps->t)) {
@@ -75,6 +107,7 @@ static ProgramTree BuildModuleTree(const parser::Name &name, const T &x) {
   const auto &spec{std::get<parser::SpecificationPart>(x.t)};
   const auto &subps{std::get<std::optional<parser::ModuleSubprogramPart>>(x.t)};
   ProgramTree node{name, spec};
+  GetGenerics(node, spec);
   if (subps) {
     for (const auto &subp :
         std::get<std::list<parser::ModuleSubprogram>>(subps->t)) {
@@ -230,4 +263,8 @@ void ProgramTree::AddEntry(const parser::EntryStmt &entryStmt) {
   entryStmts_.emplace_back(entryStmt);
 }
 
+void ProgramTree::AddGeneric(const parser::GenericSpec &generic) {
+  genericSpecs_.emplace_back(generic);
+}
+
 } // namespace Fortran::semantics