Provide a more specific diag when using keywords as identifiers

When declaring a function like func repeat(){}, the diagnostic is
"expected an identifier" but 'repeat' looks like a reasonable
identifier at first glance, so actually say why it isn't.

rdar://problem/25761380

Author: bitjammer

include/swift/AST/DiagnosticsParse.def

@@ -659,8 +659,10 @@ ERROR(expected_rangle_protocol,PointsToFirstBadToken,
 
 ERROR(expected_pattern,PointsToFirstBadToken,
       "expected pattern", ())
-ERROR(expected_pattern_is_keyword,none,
-      "keyword '%0' cannot be used as an identifier", (StringRef))
+ERROR(keyword_cant_be_identifier,none,
+      "keyword '%0' cannot be used as an identifier here", (StringRef))
+NOTE(backticks_to_escape,none,
+     "backticks can escape this name if it is important to use", ())
 ERROR(expected_rparen_tuple_pattern_list,none,
       "expected ')' at end of tuple pattern", ())
 ERROR(untyped_pattern_ellipsis,none,

include/swift/AST/DiagnosticsSema.def

@@ -462,8 +462,6 @@ ERROR(serialization_target_too_new_repl,none,
 ERROR(reserved_member_name,none,
       "type member may not be named %0, since it would conflict with the"
       " 'foo.%1' expression", (DeclName, StringRef))
-NOTE(backticks_to_escape,none,
-     "backticks can escape this name if it is important to use", ())
 
 ERROR(invalid_redecl,none,"invalid redeclaration of %0", (DeclName))
 NOTE(invalid_redecl_prev,none,

lib/Parse/ParseDecl.cpp

@@ -1,3 +1,4 @@
+
 //===--- ParseDecl.cpp - Swift Language Parser for Declarations -----------===//
 //
 // This source file is part of the Swift.org open source project
@@ -2424,6 +2425,8 @@ ParserResult<ImportDecl> Parser::parseDeclImport(ParseDeclOptions Flags,
       break;
     default:
       diagnose(Tok, diag::expected_identifier_in_decl, "import");
+      diagnose(Tok, diag::keyword_cant_be_identifier, Tok.getText());
+      diagnose(Tok, diag::backticks_to_escape);
       return nullptr;
     }
     KindLoc = consumeToken();

lib/Parse/ParsePattern.cpp

@@ -823,7 +823,8 @@ ParserResult<Pattern> Parser::parsePattern() {
   default:
     if (Tok.isKeyword() &&
         (peekToken().is(tok::colon) || peekToken().is(tok::equal))) {
-      diagnose(Tok, diag::expected_pattern_is_keyword, Tok.getText());
+      diagnose(Tok, diag::keyword_cant_be_identifier, Tok.getText());
+      diagnose(Tok, diag::backticks_to_escape);
       SourceLoc Loc = Tok.getLoc();
       consumeToken();
       return makeParserErrorResult(new (Context) AnyPattern(Loc));

lib/Parse/Parser.cpp

@@ -600,7 +600,14 @@ bool Parser::parseAnyIdentifier(Identifier &Result, SourceLoc &Loc,
   }
 
   checkForInputIncomplete();
-  diagnose(Tok, D);
+
+  if (Tok.isKeyword()) {
+    diagnose(Tok, diag::keyword_cant_be_identifier, Tok.getText());
+    diagnose(Tok, diag::backticks_to_escape);
+  } else {
+    diagnose(Tok, D);
+  }
+
   return true;
 }
 

test/Parse/invalid.swift

@@ -89,3 +89,11 @@ class VarTester {
         b += 10
     }
 }
+
+func repeat() {}
+// expected-error @-1 {{keyword 'repeat' cannot be used as an identifier here}}
+// expected-note @-2 {{backticks can escape this name if it is important to use}}
+
+let for = 2
+// expected-error @-1 {{keyword 'for' cannot be used as an identifier here}}
+// expected-note @-2 {{backticks can escape this name if it is important to use}}

test/decl/import/import.swift

@@ -43,8 +43,12 @@ import func Swift.min
 import var x // expected-error {{expected module name}}
 import struct Swift.nonexistent // expected-error {{no such decl in module}}
 
-import Swift.import.abc // expected-error 2 {{expected identifier}}
+import Swift.import.abc // expected-error {{expected identifier in import declaration}}
+// expected-error @-1 {{keyword 'import' cannot be used as an identifier here}}
+// expected-note @-2 {{backticks can escape this name if it is important to use}}
 import where Swift.Int // expected-error {{expected identifier}}
+// expected-error @-1 {{keyword 'where' cannot be used as an identifier here}}
+// expected-note @-2 {{backticks can escape this name if it is important to use}}
 import 2 // expected-error {{expected identifier}}
 
 import really.nonexistent // expected-error {{no such module 'really.nonexistent'}}

test/decl/var/variables.swift

@@ -14,7 +14,8 @@ var bfx : Int, bfy : Int
 
 _ = 10
 
-func _(_ x: Int) {} // expected-error {{expected identifier in function declaration}}
+func _(_ x: Int) {} // expected-error {{keyword '_' cannot be used as an identifier here}}
+// expected-note @-1 {{backticks can escape this name if it is important to use}}
 
 
 var self1 = self1 // expected-error {{variable used within its own initial value}}