Adds is(WRT|JVP|VJP)Identifier helper function.

Author: bgogul

include/swift/Parse/Parser.h

@@ -711,6 +711,20 @@ class Parser {
   /// Check whether the current token starts with '>'.
   bool startsWithGreater(Token Tok) { return startsWithSymbol(Tok, '>'); }
 
+  /// Returns true if token is an identifier with the given value.
+  bool isIdentifier(Token Tok, StringRef value) {
+    return Tok.is(tok::identifier) && Tok.getText() == value;
+  }
+
+  /// Returns true if token is the identifier "wrt".
+  bool isWRTIdentifier(Token tok) { return isIdentifier(Tok, "wrt"); }
+
+  /// Returns true if token is the identifier "jvp".
+  bool isJVPIdentifier(Token Tok) { return isIdentifier(Tok, "jvp"); }
+
+  /// Returns true if token is the identifier "vjp".
+  bool isVJPIdentifier(Token Tok) { return isIdentifier(Tok, "vjp"); }
+
   /// Consume the starting '<' of the current token, which may either
   /// be a complete '<' token or some kind of operator token starting with '<',
   /// e.g., '<>'.

lib/Parse/ParseDecl.cpp

@@ -1026,9 +1026,8 @@ bool Parser::parseDifferentiableAttributeArguments(
       return true;
     }
     // Check that token after comma is 'wrt:' or a function specifier label.
-    if (!Tok.is(tok::identifier) || !(Tok.getText() == "wrt" ||
-                                      Tok.getText() == "jvp" ||
-                                      Tok.getText() == "vjp")) {
+    if (!(isWRTIdentifier(Tok) || isJVPIdentifier(Tok) ||
+          isVJPIdentifier(Tok))) {
       diagnose(Tok, diag::attr_differentiable_expected_label);
       return true;
     }
@@ -1061,11 +1060,11 @@ bool Parser::parseDifferentiableAttributeArguments(
         .fixItReplace(withRespectToRange, "wrt:");
     return errorAndSkipToEnd();
   }
-  if (Tok.is(tok::identifier) && Tok.getText() == "wrt") {
+  if (isWRTIdentifier(Tok)) {
     if (parseDifferentiationParametersClause(params, AttrName))
       return true;
     // If no trailing comma or 'where' clause, terminate parsing arguments.
-    if (Tok.isNot(tok::comma) && Tok.isNot(tok::kw_where))
+    if (Tok.isNot(tok::comma, tok::kw_where))
       return false;
     if (consumeIfTrailingComma())
       return errorAndSkipToEnd();
@@ -1099,7 +1098,7 @@ bool Parser::parseDifferentiableAttributeArguments(
   bool terminateParsingArgs = false;
 
   // Parse 'jvp: <func_name>' (optional).
-  if (Tok.is(tok::identifier) && Tok.getText() == "jvp") {
+  if (isJVPIdentifier(Tok)) {
     SyntaxParsingContext JvpContext(
         SyntaxContext, SyntaxKind::DifferentiableAttributeFuncSpecifier);
     jvpSpec = DeclNameWithLoc();
@@ -1112,7 +1111,7 @@ bool Parser::parseDifferentiableAttributeArguments(
   }
 
   // Parse 'vjp: <func_name>' (optional).
-  if (Tok.is(tok::identifier) && Tok.getText() == "vjp") {
+  if (isVJPIdentifier(Tok)) {
     SyntaxParsingContext VjpContext(
         SyntaxContext, SyntaxKind::DifferentiableAttributeFuncSpecifier);
     vjpSpec = DeclNameWithLoc();