[Diagnostics] Improve diagnostic when using == instead of = for default function argument.

Author: vguerra

include/swift/AST/DiagnosticsParse.def

@@ -848,6 +848,8 @@ ERROR(expected_parameter_name,PointsToFirstBadToken,
       "expected parameter name followed by ':'", ())
 ERROR(expected_parameter_colon,PointsToFirstBadToken,
       "expected ':' following argument label and parameter name", ())
+ERROR(expected_assignment_instead_of_comparison_operator,none,
+      "expected '=' instead of '==' to assign default value for parameter", ())
 ERROR(missing_parameter_type,PointsToFirstBadToken,
       "parameter requires an explicit type", ())
 ERROR(multiple_parameter_ellipsis,none,

lib/Parse/ParsePattern.cpp

@@ -366,7 +366,13 @@ Parser::parseParameterClause(SourceLoc &leftParenLoc,
       } else {
         // Otherwise, we're not sure what is going on, but this doesn't smell
         // like a parameter.
-        diagnose(Tok, diag::expected_parameter_name);
+        if (Tok.isBinaryOperator() && Tok.getText() == "==") {
+          diagnose(Tok,
+                   diag::expected_assignment_instead_of_comparison_operator)
+              .fixItReplace(Tok.getLoc(), "=");
+        } else {
+          diagnose(Tok, diag::expected_parameter_name);
+        }
         param.isInvalid = true;
         param.FirstNameLoc = Tok.getLoc();
         TokReceiver->registerTokenKindChange(param.FirstNameLoc,

test/Parse/recovery.swift

@@ -814,3 +814,9 @@ func postfixDot(a : String) {
 func f() {
   _ = ClassWithStaticDecls.  // expected-error {{expected member name following '.'}}
 }
+
+
+// <rdar://problem/22478168> | SR-11006
+// expected-error@+2 {{expected '=' instead of '==' to assign default value for parameter}} {{21-23==}}
+// expected-error@+1 {{expected ',' separator}}
+func SR11006(a: Int == 0) {}