[flang] Change API of Scope to match std::map

The Scope can be thought of as (among other things) a mapping of Name to
Symbol. This change reflects that by changing the API to match std::map.

Original-commit: flang-compiler/f18@37f6ad73cc
Reviewed-on: https://github.com/flang-compiler/f18/pull/46
Tree-same-pre-rewrite: false

flang/lib/semantics/resolve-names.cc

@@ -228,12 +228,17 @@ private:
   void PostSubprogram(const Name &name, const std::list<Name> &dummyNames);
 
   // Helpers to make a Symbol in the current scope
-  template<typename D> Symbol &MakeSymbol(const Name &name, D &&details) {
-    return CurrScope().MakeSymbol(name, details);
+  template<typename D>
+  std::pair<Scope::iterator, bool> MakeSymbol(
+      const Name &name, const Attrs &attrs, D &&details) {
+    return CurrScope().try_emplace(name, attrs, details);
   }
   template<typename D>
-  Symbol &MakeSymbol(const Name &name, const Attrs &attrs, D &&details) {
-    return CurrScope().MakeSymbol(name, attrs, details);
+  std::pair<Scope::iterator, bool> MakeSymbol(const Name &name, D &&details) {
+    return MakeSymbol(name, Attrs(), details);
+  }
+  std::pair<Scope::iterator, bool> MakeSymbol(const Name &name) {
+    return CurrScope().try_emplace(name, UnknownDetails());
   }
 };
 
@@ -581,7 +586,8 @@ void ResolveNamesVisitor::Post(const parser::EntityDecl &x) {
   // TODO: may be under StructureStmt
   const auto &name{std::get<parser::ObjectName>(x.t)};
   // TODO: optional ArraySpec, CoarraySpec, CharLength, Initialization
-  Symbol &symbol{CurrScope().GetOrMakeSymbol(name.ToString())};
+
+  Symbol &symbol{MakeSymbol(name.ToString()).first->second};
   symbol.attrs() |= *attrs_;  // TODO: check attribute consistency
   if (symbol.has<UnknownDetails>()) {
     symbol.set_details(EntityDetails());

flang/lib/semantics/scope.cc

@@ -12,19 +12,6 @@ Scope &Scope::MakeScope(Kind kind) {
   return children_.back();
 }
 
-Symbol &Scope::GetOrMakeSymbol(const Name &name) {
-  const auto it = symbols_.find(name);
-  if (it != symbols_.end()) {
-    return it->second;
-  } else {
-    return MakeSymbol(name);
-  }
-}
-
-Symbol &Scope::MakeSymbol(const Name &name, Attrs attrs) {
-  return MakeSymbol(name, attrs, UnknownDetails());
-}
-
 static const char *ToString(Scope::Kind kind) {
   switch (kind) {
   case Scope::Kind::System: return "System";

flang/lib/semantics/scope.h

@@ -36,38 +36,42 @@ public:
   /// Make a scope nested in this one
   Scope &MakeScope(Kind kind);
 
-  /// If there is a symbol with this name already in the scope, return it.
-  /// Otherwise make a new one and return that.
-  Symbol &GetOrMakeSymbol(const Name &name);
+  using map_type = std::map<Name, Symbol>;
+  using size_type = map_type::size_type;
+  using iterator = map_type::iterator;
+  using const_iterator = map_type::const_iterator;
+
+  iterator begin() { return symbols_.begin(); }
+  iterator end() { return symbols_.end(); }
+  const_iterator begin() const { return symbols_.begin(); }
+  const_iterator end() const { return symbols_.end(); }
+
+  iterator find(const Name &name) { return symbols_.find(name); }
+  const_iterator find(const Name &name) const { return symbols_.find(name); }
+  size_type erase(const Name &name) { return symbols_.erase(name); }
 
   /// Make a Symbol with unknown details.
-  Symbol &MakeSymbol(
-      const Name &name, Attrs attrs = Attrs{});
-
+  std::pair<iterator, bool> try_emplace(
+      const Name &name, Attrs attrs = Attrs()) {
+    return try_emplace(name, attrs, UnknownDetails());
+  }
   /// Make a Symbol with provided details.
   template<typename D>
-  Symbol &MakeSymbol(const Name &name, D &&details) {
-    const auto &result =
-        symbols_.try_emplace(name, *this, name, Attrs{}, details);
-    return result.first->second;
+  std::pair<iterator, bool> try_emplace(const Name &name, D &&details) {
+    return try_emplace(name, Attrs(), details);
   }
+  /// Make a Symbol with attrs and details
   template<typename D>
-  Symbol &MakeSymbol(
+  std::pair<iterator, bool> try_emplace(
       const Name &name, Attrs attrs, D &&details) {
-    const auto &result =
-        symbols_.try_emplace(name, *this, name, attrs, details);
-    return result.first->second;
-  }
-
-  void EraseSymbol(const Name &name) {
-    symbols_.erase(name);
+    return symbols_.try_emplace(name, *this, name, attrs, details);
   }
 
 private:
   const Scope &parent_;
   const Kind kind_;
   std::list<Scope> children_;
-  std::map<Name, Symbol> symbols_;
+  map_type symbols_;
 
   friend std::ostream &operator<<(std::ostream &, const Scope &);
 };