Parse: Add fix-its for 'before:' label parse errors in the @_backDeploy attribute.

Author: tshortli

lib/Parse/ParseDecl.cpp

@@ -1848,9 +1848,11 @@ bool Parser::parseBackDeployAttribute(DeclAttributes &Attributes,
     if (Tok.is(tok::identifier) && Tok.getText() == "before") {
       consumeToken();
       if (!consumeIf(tok::colon))
-        diagnose(Tok, diag::attr_back_deploy_expected_colon_after_before);
+        diagnose(Tok, diag::attr_back_deploy_expected_colon_after_before)
+            .fixItInsertAfter(PreviousLoc, ":");
     } else {
-      diagnose(Tok, diag::attr_back_deploy_expected_before_label);
+      diagnose(Tok, diag::attr_back_deploy_expected_before_label)
+          .fixItInsertAfter(PreviousLoc, "before:");
     }
 
     // Parse the version list.

test/attr/attr_backDeploy.swift

@@ -309,23 +309,23 @@ public func knownAndUnknownMacroVersionned() {}
 public func emptyAttributeFunc() {}
 
 @available(macOS 11.0, *)
-@_backDeploy(macOS 12.0) // expected-error {{expected 'before:' in '@_backDeploy' attribute}}
+@_backDeploy(macOS 12.0) // expected-error {{expected 'before:' in '@_backDeploy' attribute}} {{14-14=before:}}
 public func missingBeforeFunc() {}
 
-@_backDeploy(before) // expected-error {{expected ':' after 'before' in '@_backDeploy' attribute}}
+@_backDeploy(before) // expected-error {{expected ':' after 'before' in '@_backDeploy' attribute}} {{20-20=:}}
 // expected-error@-1 {{expected at least one platform version in '@_backDeploy' attribute}}
 public func missingColonAfterBeforeFunc() {}
 
 @available(macOS 11.0, *)
-@_backDeploy(before macOS 12.0) // expected-error {{expected ':' after 'before' in '@_backDeploy' attribute}}
+@_backDeploy(before macOS 12.0) // expected-error {{expected ':' after 'before' in '@_backDeploy' attribute}} {{20-20=:}}
 public func missingColonBetweenBeforeAndPlatformFunc() {}
 
 @available(macOS 11.0, *)
-@_backDeploy(before: macOS 12.0,) // expected-error {{unexpected ',' separator}}
+@_backDeploy(before: macOS 12.0,) // expected-error {{unexpected ',' separator}} {{32-33=}}
 public func unexpectedTrailingCommaFunc() {}
 
 @available(macOS 11.0, iOS 14.0, *)
-@_backDeploy(before: macOS 12.0,, iOS 15.0) // expected-error {{unexpected ',' separator}}
+@_backDeploy(before: macOS 12.0,, iOS 15.0) // expected-error {{unexpected ',' separator}} {{33-34=}}
 public func extraCommaFunc() {}
 
 @_backDeploy(before:) // expected-error {{expected at least one platform version in '@_backDeploy' attribute}}