SR-11261: [Diagnostics][Qol] Parser recovery for keyword (#26596)

* Fixes SR-11261
* Improving diagnostics for multi-case declaration that uses a keyword
* Only doing pattern matching if token is not a keywork or if is a possible identifier
* Using BacktrackingScope to fix expected pattern
* Updating NameLoc with the token consumed.
* Updating Name with the consumed token

Author: LucianoPAlmeida

include/swift/AST/DiagnosticsParse.def

@@ -221,7 +221,7 @@ ERROR(expected_keyword_in_decl,none,
 ERROR(number_cant_start_decl_name,none,
       "%0 name can only start with a letter or underscore, not a number",
       (StringRef))
-ERROR(expected_identifier_after_case_comma,none,
+ERROR(expected_identifier_after_case_comma, PointsToFirstBadToken,
       "expected identifier after comma in enum 'case' declaration", ())
 ERROR(decl_redefinition,none,
       "definition conflicts with previous value", ())

lib/Parse/ParseDecl.cpp

@@ -5803,24 +5803,32 @@ Parser::parseDeclEnumCase(ParseDeclOptions Flags,
 
       // For recovery, see if the user typed something resembling a switch
       // "case" label.
-      llvm::SaveAndRestore<decltype(InVarOrLetPattern)>
-      T(InVarOrLetPattern, Parser::IVOLP_InMatchingPattern);
-      parseMatchingPattern(/*isExprBasic*/false);
-
-      if (consumeIf(tok::colon)) {
-        diagnose(CaseLoc, diag::case_outside_of_switch, "case");
-        Status.setIsParseError();
-        return Status;
-      }
-      if (CommaLoc.isValid()) {
-        diagnose(Tok, diag::expected_identifier_after_case_comma);
-        Status.setIsParseError();
-        return Status;
+      {
+        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 (NameIsKeyword) {
         diagnose(TokLoc, diag::keyword_cant_be_identifier, TokText);
         diagnose(TokLoc, diag::backticks_to_escape)
           .fixItReplace(TokLoc, "`" + TokText.str() + "`");
+        if (!Tok.isAtStartOfLine()) {
+          Name = Context.getIdentifier(Tok.getText());
+          NameLoc = consumeToken();
+        }
+      } else if (CommaLoc.isValid()) {
+        diagnose(Tok, diag::expected_identifier_after_case_comma);
+        Status.setIsParseError();
+        return Status;
       } else {
         diagnose(CaseLoc, diag::expected_identifier_in_decl, "enum 'case'");
       }

test/Parse/enum.swift

@@ -101,8 +101,8 @@ enum ImproperlyHasIVars {
 
 // We used to crash on this.  rdar://14678675
 enum rdar14678675 {
-  case U1,
-  case U2 // expected-error{{expected identifier after comma in enum 'case' declaration}}
+  case U1, // expected-error{{expected identifier after comma in enum 'case' declaration}}
+  case U2 
   case U3
 }
 
@@ -125,10 +125,10 @@ enum Recovery5 {
   // expected-error@-2{{extraneous '.' in enum 'case' declaration}} {{14-15=}}
 }
 enum Recovery6 {
-  case Snout, _; // expected-error {{expected identifier after comma in enum 'case' declaration}}
-  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 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=`_`}} expected-note {{'_' previously declared here}}
+  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=`_`}} expected-error {{invalid redeclaration of '_'}}
+  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}}
@@ -552,3 +552,42 @@ enum SE0155 {
   // expected-note@-1 {{did you mean to remove the empty associated value list?}} {{17-18=}}
   // expected-note@-2 {{did you mean to explicitly add a 'Void' associated value?}} {{17-17=Void}}
 }
+
+// SR-11261
+enum SR11261 {
+  case identifier
+  case operator // expected-error {{keyword 'operator' cannot be used as an identifier here}} expected-note {{if this name is unavoidable, use backticks to escape it}} {{8-16=`operator`}}
+  case identifier2
+}
+
+enum SR11261_var {
+  case identifier
+  case var // expected-error {{keyword 'var' cannot be used as an identifier here}} expected-note {{if this name is unavoidable, use backticks to escape it}} {{8-11=`var`}}
+  case identifier2
+}
+
+enum SR11261_underscore {
+  case identifier
+  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 identifier2
+}
+
+enum SR11261_Comma {
+  case a, b, c, func, d // expected-error {{keyword 'func' cannot be used as an identifier here}} expected-note {{if this name is unavoidable, use backticks to escape it}} {{17-21=`func`}}
+}
+
+enum SR11261_Newline {
+  case identifier1
+  case identifier2
+  case 
+  case identifier // expected-error {{keyword 'case' cannot be used as an identifier here}} expected-note {{if this name is unavoidable, use backticks to escape it}} {{3-7=`case`}}
+}
+
+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}}
+}

test/stmt/statements.swift

@@ -637,6 +637,6 @@ outerLoop1: repeat { // expected-note {{did you mean 'outerLoop1'?}} {{14-23=out
 
 // Errors in case syntax
 class
-case, // expected-error {{expected identifier in enum 'case' declaration}} expected-error {{expected pattern}}
-case  // expected-error {{expected identifier after comma in enum 'case' declaration}} expected-error {{expected identifier in enum 'case' declaration}} expected-error {{enum 'case' is not allowed outside of an enum}} expected-error {{expected pattern}}
+case, // expected-error {{expected identifier in enum 'case' declaration}} expected-error {{expected identifier after comma in enum 'case' declaration}}
+case  // expected-error {{expected identifier in enum 'case' declaration}} expected-error {{enum 'case' is not allowed outside of an enum}}
 // NOTE: EOF is important here to properly test a code path that used to crash the parser