Using BacktrackingScope to fix expected pattern

Author: LucianoPAlmeida

lib/Parse/ParseDecl.cpp

@@ -5767,32 +5767,32 @@ Parser::parseDeclEnumCase(ParseDeclOptions Flags,
       SourceLoc TokLoc = Tok.getLoc();
       StringRef TokText = Tok.getText();
 
-      if (!NameIsKeyword || Tok.isIdentifierOrUnderscore()) {
-        // For recovery, see if the user typed something resembling a switch
-        // "case" label.
+      // For recovery, see if the user typed something resembling a switch
+      // "case" label.
+      {
+        BacktrackingScope backtrack(*this);
         llvm::SaveAndRestore<decltype(InVarOrLetPattern)>
         T(InVarOrLetPattern, Parser::IVOLP_InMatchingPattern);
         parseMatchingPattern(/*isExprBasic*/false);
+        
+        if (consumeIf(tok::colon)) {
+          backtrack.cancelBacktrack();
+          diagnose(CaseLoc, diag::case_outside_of_switch, "case");
+          Status.setIsParseError();
+          return Status;
+        }
       }
-
-      if (consumeIf(tok::colon)) {
-        diagnose(CaseLoc, diag::case_outside_of_switch, "case");
+      if (CommaLoc.isValid() && !NameIsKeyword) {
+        diagnose(CommaLoc, diag::expected_identifier_after_case_comma);
         Status.setIsParseError();
         return Status;
-      }
-
-      if (NameIsKeyword) {
+      } else if (NameIsKeyword) {
         diagnose(TokLoc, diag::keyword_cant_be_identifier, TokText);
         diagnose(TokLoc, diag::backticks_to_escape)
           .fixItReplace(TokLoc, "`" + TokText.str() + "`");
         if (!Tok.isAtStartOfLine())
           consumeToken();
       } else {
-        if (CommaLoc.isValid()) {
-          diagnose(Tok, diag::expected_identifier_after_case_comma);
-          Status.setIsParseError();
-          return Status;
-        }
         diagnose(CaseLoc, diag::expected_identifier_in_decl, "enum 'case'");
       }
     }

test/Parse/enum.swift

@@ -127,8 +127,8 @@ enum Recovery5 {
 enum Recovery6 {
   case Snout, _; // expected-error {{keyword '_' cannot be used as an identifier here}} expected-note {{if this name is unavoidable, use backticks to escape it}} {{15-16=`_`}}
   case _; // expected-error {{keyword '_' cannot be used as an identifier here}} expected-note {{if this name is unavoidable, use backticks to escape it}} {{8-9=`_`}}
-  case Tusk, // expected-error {{expected pattern}}
-} // expected-error {{expected identifier after comma in enum 'case' declaration}}
+  case Tusk, // expected-error {{expected identifier after comma in enum 'case' declaration}}
+} 
 
 enum RawTypeEmpty : Int {} // expected-error {{an enum with no cases cannot declare a raw type}} expected-note {{do you want to add protocol stubs?}}
 // expected-error@-1{{'RawTypeEmpty' declares raw type 'Int', but does not conform to RawRepresentable and conformance could not be synthesized}}
@@ -574,4 +574,8 @@ enum SR11261_Newline {
 enum SR11261_Newline2 {
   case 
   func foo() {} // expected-error {{keyword 'func' cannot be used as an identifier here}} expected-note {{if this name is unavoidable, use backticks to escape it}} {{3-7=`func`}}
+}
+
+enum SR11261_PatternMatching {
+  case let .foo(x, y): // expected-error {{'case' label can only appear inside a 'switch' statement}}
 }