[AST] Add IterableDeclContext::getParsedMembers().

Provide an accessor for retrieving the parsed members, generalizing
`ParseMembersRequest` so it can provide the parsed members for
deserialized/synthesized declarations as well. This is the counterpart
to the recently-generalized `getSemanticMembers()`; together, these
should suffice for most (all?) clients of `getMembers()`.

Author: DougGregor

include/swift/AST/DeclContext.h

@@ -783,6 +783,11 @@ class IterableDeclContext {
   /// Retrieve the set of members in this context.
   DeclRange getMembers() const;
 
+  /// Get the members that were syntactically present in the source code,
+  /// and will not contain any members that are implicitly synthesized by
+  /// the implementation.
+  ArrayRef<Decl *> getParsedMembers() const;
+
   /// Get all the members that are semantically within this context,
   /// including any implicitly-synthesized members.
   /// The resulting list of members will be stable across translation units.

lib/AST/DeclContext.cpp

@@ -793,6 +793,15 @@ DeclRange IterableDeclContext::getMembers() const {
   return getCurrentMembersWithoutLoading();
 }
 
+ArrayRef<Decl *> IterableDeclContext::getParsedMembers() const {
+  ASTContext &ctx = getASTContext();
+  auto mutableThis = const_cast<IterableDeclContext *>(this);
+  return evaluateOrDefault(
+      ctx.evaluator, ParseMembersRequest{mutableThis},
+      FingerprintAndMembers())
+    .members;
+}
+
 ArrayRef<Decl *> IterableDeclContext::getSemanticMembers() const {
   ASTContext &ctx = getASTContext();
   return evaluateOrDefault(
@@ -899,10 +908,7 @@ void IterableDeclContext::loadAllMembers() const {
     // members to this context, this call is important for recording the
     // dependency edge.
     auto mutableThis = const_cast<IterableDeclContext *>(this);
-    auto members =
-        evaluateOrDefault(ctx.evaluator, ParseMembersRequest{mutableThis},
-                          FingerprintAndMembers())
-            .members;
+    auto members = getParsedMembers();
 
     // If we haven't already done so, add these members to this context.
     if (!AddedParsedMembers) {

lib/Parse/ParseRequests.cpp

@@ -49,15 +49,29 @@ void swift::simple_display(llvm::raw_ostream &out,
 FingerprintAndMembers
 ParseMembersRequest::evaluate(Evaluator &evaluator,
                               IterableDeclContext *idc) const {
-  SourceFile &sf = *idc->getAsGenericContext()->getParentSourceFile();
-  unsigned bufferID = *sf.getBufferID();
+  SourceFile *sf = idc->getAsGenericContext()->getParentSourceFile();
+  ASTContext &ctx = idc->getDecl()->getASTContext();
+  if (!sf) {
+    // If there is no parent source file, this is a deserialized or synthesized
+    // declaration context, in which case `getMembers()` has all of the members.
+    // Filter out the implicitly-generated ones.
+    SmallVector<Decl *, 4> members;
+    for (auto decl : idc->getMembers()) {
+      if (!decl->isImplicit()) {
+        members.push_back(decl);
+      }
+    }
+
+    return FingerprintAndMembers{None, ctx.AllocateCopy(members)};
+  }
+
+  unsigned bufferID = *sf->getBufferID();
 
   // Lexer diaganostics have been emitted during skipping, so we disable lexer's
   // diagnostic engine here.
-  Parser parser(bufferID, sf, /*No Lexer Diags*/nullptr, nullptr, nullptr);
+  Parser parser(bufferID, *sf, /*No Lexer Diags*/nullptr, nullptr, nullptr);
   // Disable libSyntax creation in the delayed parsing.
   parser.SyntaxContext->disable();
-  ASTContext &ctx = idc->getDecl()->getASTContext();
   auto declsAndHash = parser.parseDeclListDelayed(idc);
   FingerprintAndMembers fingerprintAndMembers = {declsAndHash.second,
                                                  declsAndHash.first};