[Macros] Fix name lookup of macro parameters in the definition.

This enables macros to be defined in terms of other macros.

Author: DougGregor

include/swift/AST/ASTScope.h

@@ -1215,6 +1215,26 @@ class MacroDeclScope final : public ASTScopeImpl {
 
 protected:
   NullablePtr<const GenericParamList> genericParams() const override;
+  bool lookupLocalsOrMembers(DeclConsumer) const override;
+};
+
+/// The scope introduced for the definition of a macro, which follows the `=`.
+class MacroDefinitionScope final : public ASTScopeImpl {
+public:
+  Expr *const definition;
+
+  MacroDefinitionScope(Expr *definition) : definition(definition) {}
+
+  virtual ~MacroDefinitionScope() {}
+  SourceRange
+  getSourceRangeOfThisASTNode(bool omitAssertions = false) const override;
+  std::string getClassName() const override;
+
+private:
+  void expandAScopeThatDoesNotCreateANewInsertionPoint(ScopeCreator &);
+
+protected:
+  ASTScopeImpl *expandSpecifically(ScopeCreator &scopeCreator) override;
 };
 
 class AbstractStmtScope : public ASTScopeImpl {

lib/AST/ASTScope.cpp

@@ -151,6 +151,7 @@ DEFINE_GET_CLASS_NAME(DifferentiableAttributeScope)
 DEFINE_GET_CLASS_NAME(SubscriptDeclScope)
 DEFINE_GET_CLASS_NAME(EnumElementScope)
 DEFINE_GET_CLASS_NAME(MacroDeclScope)
+DEFINE_GET_CLASS_NAME(MacroDefinitionScope)
 DEFINE_GET_CLASS_NAME(IfStmtScope)
 DEFINE_GET_CLASS_NAME(WhileStmtScope)
 DEFINE_GET_CLASS_NAME(GuardStmtScope)

lib/AST/ASTScopeCreation.cpp

@@ -723,6 +723,7 @@ NO_NEW_INSERTION_POINT(IfStmtScope)
 NO_NEW_INSERTION_POINT(RepeatWhileScope)
 NO_NEW_INSERTION_POINT(SubscriptDeclScope)
 NO_NEW_INSERTION_POINT(MacroDeclScope)
+NO_NEW_INSERTION_POINT(MacroDefinitionScope)
 NO_NEW_INSERTION_POINT(SwitchStmtScope)
 NO_NEW_INSERTION_POINT(WhileStmtScope)
 
@@ -1115,9 +1116,19 @@ void MacroDeclScope::expandAScopeThatDoesNotCreateANewInsertionPoint(
   auto *leaf = scopeCreator.addNestedGenericParamScopesToTree(
       decl, getPotentiallyOpaqueGenericParams(decl), this);
   if (decl->parameterList) {
-    scopeCreator.constructExpandAndInsert<ParameterListScope>(
+    leaf = scopeCreator.constructExpandAndInsert<ParameterListScope>(
         leaf, decl->parameterList, nullptr);
   }
+  if (auto def = decl->definition) {
+    scopeCreator
+      .constructExpandAndInsert<MacroDefinitionScope>(leaf, def);
+  }
+}
+
+void
+MacroDefinitionScope::expandAScopeThatDoesNotCreateANewInsertionPoint(
+    ScopeCreator &scopeCreator) {
+  scopeCreator.addToScopeTree(ASTNode(definition), this);
 }
 
 void CaptureListScope::expandAScopeThatDoesNotCreateANewInsertionPoint(

lib/AST/ASTScopeLookup.cpp

@@ -260,6 +260,17 @@ NullablePtr<const GenericParamList> MacroDeclScope::genericParams() const {
   return decl->getParsedGenericParams();
 }
 
+bool MacroDeclScope::lookupLocalsOrMembers(
+    DeclConsumer consumer) const {
+  if (auto *paramList = decl->parameterList) {
+    for (auto *paramDecl : *paramList)
+      if (consumer.consume({paramDecl}))
+        return true;
+  }
+
+  return false;
+}
+
 #pragma mark lookInMyGenericParameters
 
 std::pair<bool, NullablePtr<const GenericParamList>>

lib/AST/ASTScopeSourceRange.cpp

@@ -143,6 +143,11 @@ SourceRange MacroDeclScope::getSourceRangeOfThisASTNode(
   return decl->getSourceRangeIncludingAttrs();
 }
 
+SourceRange MacroDefinitionScope::getSourceRangeOfThisASTNode(
+    const bool omitAssertions) const {
+  return definition->getSourceRange();
+}
+
 SourceRange
 EnumElementScope::getSourceRangeOfThisASTNode(const bool omitAssertions) const {
   return decl->getSourceRange();

lib/AST/ASTVerifier.cpp

@@ -477,7 +477,7 @@ class Verifier : public ASTWalker {
         // For @objc enums, we serialize the pre-type-checked integer
         // literal raw values, and thus when they are deserialized
         // they do not have a type on them.
-        if (!isa<IntegerLiteralExpr>(E)) {
+        if (!isa<IntegerLiteralExpr>(E) && !isa<MacroExpansionExpr>(E)) {
           Out << "expression has no type\n";
           E->dump(Out);
           abort();

lib/AST/ASTWalker.cpp

@@ -422,6 +422,13 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
         return true;
     }
 
+    if (auto def = MD->definition) {
+      if (auto newDef = doIt(def))
+        MD->definition = newDef;
+      else
+        return true;
+    }
+
     // Visit trailing requirements
     if (WalkGenerics && visitTrailingRequirements(MD))
        return true;