Add tok::colon_colon to parser

This breaks some diagnostics in expr/primary/unqualified_name.swift; I’ll continue adding the feature and then revisit these to see how I can support them.

Author: beccadax

include/swift/Parse/Parser.h

@@ -839,6 +839,17 @@ class Parser {
   consumeStartingCharacterOfCurrentToken(tok Kind = tok::oper_binary_unspaced,
                                          size_t Len = 1);
 
+  /// If the next token is \c tok::colon, consume it; if the next token is
+  /// \c tok::colon_colon, split it into two \c tok::colons and consume the
+  /// first; otherwise, do nothing and return false.
+  bool consumeIfColonSplittingDoubles() {
+    if (!Tok.isAny(tok::colon, tok::colon_colon))
+      return false;
+
+    consumeStartingCharacterOfCurrentToken(tok::colon);
+    return true;
+  }
+
   //===--------------------------------------------------------------------===//
   // Primitive Parsing
 

lib/Parse/Lexer.cpp

@@ -2412,9 +2412,15 @@ void Lexer::lexImpl() {
 
   case ',': return formToken(tok::comma, TokStart);
   case ';': return formToken(tok::semi, TokStart);
-  case ':': return formToken(tok::colon, TokStart);
   case '\\': return formToken(tok::backslash, TokStart);
 
+  case ':':
+    if (CurPtr[0] == ':') {
+      CurPtr++;
+      return formToken(tok::colon_colon, TokStart);
+    }
+    return formToken(tok::colon, TokStart);
+
   case '#':
     if (unsigned CustomDelimiterLen = advanceIfCustomDelimiter(CurPtr, Diags))
       return lexStringLiteral(CustomDelimiterLen);

lib/Parse/ParseDecl.cpp

@@ -1396,11 +1396,10 @@ void Parser::parseObjCSelector(SmallVector<Identifier, 4> &Names,
     SyntaxParsingContext SelectorPieceContext(SyntaxContext,
                                               SyntaxKind::ObjCSelectorPiece);
     // Empty selector piece.
-    if (Tok.is(tok::colon)) {
+    if (consumeIfColonSplittingDoubles()) {
       Names.push_back(Identifier());
-      NameLocs.push_back(Tok.getLoc());
+      NameLocs.push_back(PreviousLoc);
       IsNullarySelector = false;
-      consumeToken();
       continue;
     }
 
@@ -1411,8 +1410,7 @@ void Parser::parseObjCSelector(SmallVector<Identifier, 4> &Names,
       consumeToken();
 
       // If we have a colon, consume it.
-      if (Tok.is(tok::colon)) {
-        consumeToken();
+      if (consumeIfColonSplittingDoubles()) {
         IsNullarySelector = false;
         continue;
       }

lib/Parse/ParseExpr.cpp

@@ -2147,9 +2147,25 @@ ParserResult<Expr> Parser::parseExprStringLiteral() {
                                       AppendingExpr));
 }
 
+/// Equivalent to \c Tok.is(tok::colon), but pretends that \c tok::colon_colon
+/// doesn't exist if \c EnableExperimentalModuleSelector is disabled.
+static bool isColon(Parser &P, Token Tok) {
+  // FIXME: Introducing tok::colon_colon broke diag::empty_arg_label_underscore.
+  // We only care about tok::colon_colon when module selectors are turned on, so
+  // when they are turned off, this function works around the bug by treating
+  // tok::colon_colon as a synonym for tok::colon. However, the bug still exists
+  // when EnableExperimentalModuleSelector is true. We will need to address this
+  // before the feature can be released.
+
+  if (P.Context.LangOpts.EnableExperimentalModuleSelector)
+    return Tok.is(tok::colon);
+
+  return Tok.isAny(tok::colon, tok::colon_colon);
+}
+
 void Parser::parseOptionalArgumentLabel(Identifier &name, SourceLoc &loc) {
   // Check to see if there is an argument label.
-  if (Tok.canBeArgumentLabel() && peekToken().is(tok::colon)) {
+  if (Tok.canBeArgumentLabel() && isColon(*this, peekToken())) {
     auto text = Tok.getText();
 
     // If this was an escaped identifier that need not have been escaped, say
@@ -2167,7 +2183,7 @@ void Parser::parseOptionalArgumentLabel(Identifier &name, SourceLoc &loc) {
     }
 
     loc = consumeArgumentLabel(name, /*diagnoseDollarPrefix=*/false);
-    consumeToken(tok::colon);
+    consumeIfColonSplittingDoubles();
   }
 }
 
@@ -2192,7 +2208,7 @@ static bool tryParseArgLabelList(Parser &P, Parser::DeclNameOptions flags,
       flags.contains(Parser::DeclNameFlag::AllowZeroArgCompoundNames) &&
       next.is(tok::r_paren);
   // An argument label.
-  bool nextIsArgLabel = next.canBeArgumentLabel() || next.is(tok::colon);
+  bool nextIsArgLabel = next.canBeArgumentLabel() || isColon(P, next);
   // An editor placeholder.
   bool nextIsPlaceholder = Identifier::isEditorPlaceholder(next.getText());
 
@@ -2208,11 +2224,11 @@ static bool tryParseArgLabelList(Parser &P, Parser::DeclNameOptions flags,
     SyntaxParsingContext ArgCtxt(P.SyntaxContext, SyntaxKind::DeclNameArgument);
 
     // If we see a ':', the user forgot the '_';
-    if (P.Tok.is(tok::colon)) {
-      P.diagnose(P.Tok, diag::empty_arg_label_underscore)
-          .fixItInsert(P.Tok.getLoc(), "_");
+    if (P.consumeIfColonSplittingDoubles()) {
+      P.diagnose(P.PreviousLoc, diag::empty_arg_label_underscore)
+          .fixItInsert(P.PreviousLoc, "_");
       argumentLabels.push_back(Identifier());
-      argumentLabelLocs.push_back(P.consumeToken(tok::colon));
+      argumentLabelLocs.push_back(P.PreviousLoc);
     }
 
     Identifier argName;

utils/gyb_syntax_support/Token.py

@@ -233,6 +233,7 @@ def macro_name(self):
     Punctuator('Ellipsis', 'ellipsis', text='...', serialization_code=118),
     Punctuator('Colon', 'colon', text=':', requires_trailing_space=True,
                serialization_code=82),
+    Punctuator('ColonColon', 'colon_colon', text='::', serialization_code=124),
     Punctuator('Semicolon', 'semi', text=';', serialization_code=83),
     Punctuator('Equal', 'equal', text='=', requires_leading_space=True,
                requires_trailing_space=True, serialization_code=86),