[Parser] Allow $ prefixes on argument labels and closure parameter

declarations.

Author: hborla

Diff for: include/swift/Parse/Parser.h

@@ -563,15 +563,16 @@ class Parser {
     return consumeToken();
   }
 
-  SourceLoc consumeArgumentLabel(Identifier &Result) {
+  SourceLoc consumeArgumentLabel(Identifier &Result,
+                                 bool diagnoseDollarPrefix) {
     assert(Tok.canBeArgumentLabel());
     assert(Result.empty());
     if (!Tok.is(tok::kw__)) {
       Tok.setKind(tok::identifier);
       Result = Context.getIdentifier(Tok.getText());
 
       if (Tok.getText()[0] == '$')
-        diagnoseDollarIdentifier(Tok, /*diagnoseDollarPrefix=*/true);
+        diagnoseDollarIdentifier(Tok, diagnoseDollarPrefix);
     }
     return consumeToken();
   }

Diff for: lib/Parse/ParseExpr.cpp

@@ -2048,7 +2048,7 @@ void Parser::parseOptionalArgumentLabel(Identifier &name, SourceLoc &loc) {
           .fixItRemoveChars(end.getAdvancedLoc(-1), end);
     }
 
-    loc = consumeArgumentLabel(name);
+    loc = consumeArgumentLabel(name, /*diagnoseDollarPrefix=*/false);
     consumeToken(tok::colon);
   }
 }
@@ -2599,7 +2599,7 @@ ParserStatus Parser::parseClosureSignatureIfPresent(
         Identifier name;
         SourceLoc nameLoc;
         if (Tok.is(tok::identifier)) {
-          nameLoc = consumeIdentifier(name, /*diagnoseDollarPrefix=*/true);
+          nameLoc = consumeIdentifier(name, /*diagnoseDollarPrefix=*/false);
         } else {
           nameLoc = consumeToken(tok::kw__);
         }
@@ -3175,7 +3175,7 @@ Parser::parseTrailingClosures(bool isExprBasic, SourceRange calleeRange,
     SyntaxParsingContext ClosureCtx(SyntaxContext,
                                     SyntaxKind::MultipleTrailingClosureElement);
     Identifier label;
-    auto labelLoc = consumeArgumentLabel(label);
+    auto labelLoc = consumeArgumentLabel(label, /*diagnoseDollarPrefix=*/false);
     consumeToken(tok::colon);
     ParserResult<Expr> closure;
     if (Tok.is(tok::l_brace)) {

Diff for: lib/Parse/ParsePattern.cpp

@@ -276,11 +276,13 @@ Parser::parseParameterClause(SourceLoc &leftParenLoc,
 
     if (startsParameterName(*this, isClosure)) {
       // identifier-or-none for the first name
-      param.FirstNameLoc = consumeArgumentLabel(param.FirstName);
+      param.FirstNameLoc = consumeArgumentLabel(param.FirstName,
+                                                /*diagnoseDollarPrefix=*/!isClosure);
 
       // identifier-or-none? for the second name
       if (Tok.canBeArgumentLabel())
-        param.SecondNameLoc = consumeArgumentLabel(param.SecondName);
+        param.SecondNameLoc = consumeArgumentLabel(param.SecondName,
+                                                   /*diagnoseDollarPrefix=*/true);
 
       // Operators, closures, and enum elements cannot have API names.
       if ((paramContext == ParameterContextKind::Operator ||

Diff for: lib/Parse/ParseType.cpp

@@ -1020,11 +1020,13 @@ ParserResult<TypeRepr> Parser::parseTypeTupleBody() {
         && (peekToken().is(tok::colon)
             || peekToken().canBeArgumentLabel())) {
       // Consume a name.
-      element.NameLoc = consumeArgumentLabel(element.Name);
+      element.NameLoc = consumeArgumentLabel(element.Name,
+                                             /*diagnoseDollarPrefix=*/true);
 
       // If there is a second name, consume it as well.
       if (Tok.canBeArgumentLabel())
-        element.SecondNameLoc = consumeArgumentLabel(element.SecondName);
+        element.SecondNameLoc = consumeArgumentLabel(element.SecondName,
+                                                     /*diagnoseDollarPrefix=*/true);
 
       // Consume the ':'.
       if (consumeIf(tok::colon, element.ColonLoc)) {