[AST] Remove parsing ASTStages

Now that the parsing stage has been
requestified, these are no longer
meaningful.

Author: hamishknight

include/swift/AST/SourceFile.h

@@ -306,10 +306,8 @@ class SourceFile final : public FileUnit {
   const SourceFileKind Kind;
 
   enum ASTStage_t {
-    /// Parsing is underway.
-    Parsing,
-    /// Parsing has completed.
-    Parsed,
+    /// The source file is not name bound or type checked.
+    Unprocessed,
     /// Name binding has completed.
     NameBound,
     /// Type checking has completed.
@@ -321,7 +319,7 @@ class SourceFile final : public FileUnit {
   ///
   /// Only files that have been fully processed (i.e. type-checked) will be
   /// forwarded on to IRGen.
-  ASTStage_t ASTStage = Parsing;
+  ASTStage_t ASTStage = Unprocessed;
 
   SourceFile(ModuleDecl &M, SourceFileKind K, Optional<unsigned> bufferID,
              ImplicitModuleImportKind ModImpKind, bool KeepParsedTokens = false,

lib/AST/Module.cpp

@@ -1192,7 +1192,14 @@ void ModuleDecl::getImportedModules(SmallVectorImpl<ImportedModule> &modules,
 void
 SourceFile::getImportedModules(SmallVectorImpl<ModuleDecl::ImportedModule> &modules,
                                ModuleDecl::ImportFilter filter) const {
-  assert(ASTStage >= Parsed || Kind == SourceFileKind::SIL);
+  // FIXME: Ideally we should assert that the file has been name bound before
+  // calling this function. However unfortunately that can cause issues for
+  // overlays which can depend on a Clang submodule for the underlying framework
+  // they are overlaying, which causes us to attempt to load the overlay again.
+  // We need to find a way to ensure that an overlay dependency with the same
+  // name as the overlay always loads the underlying Clang module. We currently
+  // handle this for a direct import from the overlay, but not when it happens
+  // through other imports.
   assert(filter && "no imports requested?");
   for (auto desc : Imports) {
     ModuleDecl::ImportFilter requiredFilter;

lib/Frontend/Frontend.cpp

@@ -759,11 +759,7 @@ void CompilerInstance::performSema() {
 }
 
 void CompilerInstance::performSemaUpTo(SourceFile::ASTStage_t LimitStage) {
-  // FIXME: A lot of the logic in `performParseOnly` is a stripped-down version
-  // of the logic in `performSemaUpTo`.  We should try to unify them over time.
-  if (LimitStage <= SourceFile::Parsed) {
-    return performParseOnly();
-  }
+  assert(LimitStage > SourceFile::Unprocessed);
 
   FrontendStatsTracer tracer(getStatsReporter(), "perform-sema");
 

lib/Parse/ParseRequests.cpp

@@ -177,8 +177,7 @@ void ParseSourceFileRequest::cacheResult(ArrayRef<Decl *> decls) const {
   assert(!SF->Decls);
   SF->Decls = decls;
 
-  // Note that the source file is fully parsed and verify it.
-  SF->ASTStage = SourceFile::Parsed;
+  // Verify the parsed source file.
   verify(*SF);
 }