[libSyntax] Fix parsing for KeyPath

Author: ahoppen

lib/Parse/ParseDecl.cpp

@@ -3131,12 +3131,9 @@ ParserStatus Parser::parseDeclItem(bool &PreviousHadSemi,
   ParserResult<Decl> Result;
   SyntaxParsingContext DeclContext(SyntaxContext,
                                    SyntaxKind::MemberDeclListItem);
-  {
-    SyntaxParsingContext DeclContext(SyntaxContext, SyntaxContextKind::Decl);
-    Result = parseDecl(Options, handler);
-    if (Result.isParseError())
-      skipUntilDeclRBrace(tok::semi, tok::pound_endif);
-  }
+  Result = parseDecl(Options, handler);
+  if (Result.isParseError())
+    skipUntilDeclRBrace(tok::semi, tok::pound_endif);
   SourceLoc SemiLoc;
   PreviousHadSemi = consumeIf(tok::semi, SemiLoc);
   if (PreviousHadSemi && Result.isNonNull())

lib/Parse/ParseExpr.cpp

@@ -582,7 +582,6 @@ ParserResult<Expr> Parser::parseExprKeyPath() {
   // Consume '\'.
   SourceLoc backslashLoc = consumeToken(tok::backslash);
   llvm::SaveAndRestore<SourceLoc> slashLoc(SwiftKeyPathSlashLoc, backslashLoc);
-  SyntaxParsingContext ExprCtx(SyntaxContext, SyntaxContextKind::Expr);
 
   // FIXME: diagnostics
   ParserResult<Expr> rootResult, pathResult;
@@ -598,14 +597,19 @@ ParserResult<Expr> Parser::parseExprKeyPath() {
   if (startsWithSymbol(Tok, '.')) {
     llvm::SaveAndRestore<Expr*> S(SwiftKeyPathRoot, rootResult.getPtrOrNull());
 
+    SyntaxParsingContext ExprContext(SyntaxContext, SyntaxContextKind::Expr);
+
     auto dotLoc = Tok.getLoc();
     // For uniformity, \.foo is parsed as if it were MAGIC.foo, so we need to
     // make sure the . is there, but parsing the ? in \.? as .? doesn't make
     // sense. This is all made more complicated by .?. being considered an
     // operator token, and a single one at that (which means
     // peekToken().is(tok::identifier) is incorrect: it is true for .?.foo).
-    if (Tok.getLength() != 1 || !peekToken().is(tok::identifier))
+    if (Tok.getLength() != 1 || !peekToken().is(tok::identifier)) {
+      SyntaxParsingContext KeyPathBaseContext(SyntaxContext,
+                                              SyntaxKind::KeyPathBaseExpr);
       consumeStartingCharacterOfCurrentToken(tok::period);
+    }
 
     auto inner = makeParserResult(new (Context) KeyPathDotExpr(dotLoc));
     bool unusedHasBindOptional = false;

test/Syntax/Outputs/round_trip_parse_gen.swift.withkinds

@@ -437,10 +437,10 @@ func foo<FunctionSignature><ParameterClause>() </ParameterClause></FunctionSigna
 }</CodeBlock></FunctionDecl><FunctionDecl>
 
 func keypath<FunctionSignature><ParameterClause>() </ParameterClause></FunctionSignature><CodeBlock>{<SequenceExpr><DiscardAssignmentExpr>
-  _ </DiscardAssignmentExpr><AssignmentExpr>= </AssignmentExpr><KeyPathExpr>\<IdentifierExpr>a</IdentifierExpr>.?.b</KeyPathExpr></SequenceExpr><SequenceExpr><DiscardAssignmentExpr>
+  _ </DiscardAssignmentExpr><AssignmentExpr>= </AssignmentExpr><KeyPathExpr>\<IdentifierExpr>a</IdentifierExpr><MemberAccessExpr><OptionalChainingExpr><KeyPathBaseExpr>.</KeyPathBaseExpr>?</OptionalChainingExpr>.b</MemberAccessExpr></KeyPathExpr></SequenceExpr><SequenceExpr><DiscardAssignmentExpr>
   _ </DiscardAssignmentExpr><AssignmentExpr>= </AssignmentExpr><KeyPathExpr>\<MemberAccessExpr><MemberAccessExpr><IdentifierExpr>a</IdentifierExpr>.b</MemberAccessExpr>.c</MemberAccessExpr></KeyPathExpr></SequenceExpr><SequenceExpr><DiscardAssignmentExpr>
   _ </DiscardAssignmentExpr><AssignmentExpr>= </AssignmentExpr><KeyPathExpr>\<SubscriptExpr><MemberAccessExpr><IdentifierExpr>a</IdentifierExpr>.b</MemberAccessExpr>[<FunctionCallArgument><IntegerLiteralExpr>1</IntegerLiteralExpr></FunctionCallArgument>]</SubscriptExpr></KeyPathExpr></SequenceExpr><SequenceExpr><DiscardAssignmentExpr>
-  _ </DiscardAssignmentExpr><AssignmentExpr>= </AssignmentExpr><KeyPathExpr>\<MemberAccessExpr>.a.b</MemberAccessExpr></KeyPathExpr></SequenceExpr><SequenceExpr><DiscardAssignmentExpr>
+  _ </DiscardAssignmentExpr><AssignmentExpr>= </AssignmentExpr><KeyPathExpr>\<MemberAccessExpr><MemberAccessExpr>.a</MemberAccessExpr>.b</MemberAccessExpr></KeyPathExpr></SequenceExpr><SequenceExpr><DiscardAssignmentExpr>
   _ </DiscardAssignmentExpr><AssignmentExpr>= </AssignmentExpr><ObjcKeyPathExpr>#keyPath(<ObjcNamePiece>a.</ObjcNamePiece><ObjcNamePiece>b.</ObjcNamePiece><ObjcNamePiece>c</ObjcNamePiece>)</ObjcKeyPathExpr></SequenceExpr>
 }</CodeBlock></FunctionDecl><FunctionDecl>
 func objcSelector<FunctionSignature><ParameterClause>() </ParameterClause></FunctionSignature><CodeBlock>{<SequenceExpr><DiscardAssignmentExpr>

utils/gyb_syntax_support/ExprNodes.py

@@ -300,7 +300,9 @@
     # a.b
     Node('MemberAccessExpr', kind='Expr',
          children=[
-             Child("Base", kind='Expr'),
+             # The base needs to be optional to parse expressions in key paths
+             # like \.a
+             Child("Base", kind='Expr', is_optional=True),
              Child("Dot", kind='PeriodToken'),
              Child("Name", kind='Token'),
              Child('DeclNameArguments', kind='DeclNameArguments',
@@ -496,9 +498,17 @@
     Node('KeyPathExpr', kind='Expr',
          children=[
              Child('Backslash', kind='BackslashToken'),
+             Child('RootExpr', kind='IdentifierExpr', is_optional=True), 
              Child('Expression', kind='Expr'),
          ]),
 
+    # The period in the key path serves as the base on which the 
+    # right-hand-side of the key path is evaluated
+    Node('KeyPathBaseExpr', kind='Expr', 
+         children=[
+             Child('Period', kind='PeriodToken'),
+         ]),
+
     # e.g. "a." or "a"
     Node('ObjcNamePiece', kind='Syntax',
          children=[