Parse: An empty escaped identifier is entirely whitespace

Author: slavapestov

lib/Parse/Lexer.cpp

@@ -661,7 +661,7 @@ static bool advanceIfValidContinuationOfOperator(char const *&ptr,
 /// Returns true if the given string is entirely whitespace (considering only
 /// those whitespace code points permitted in raw identifiers).
 static bool isEntirelyWhitespace(StringRef string) {
-  if (string.empty()) return false;
+  if (string.empty()) return true;
   char const *p = string.data(), *end = string.end();
   if (!advanceIf(p, end, isPermittedRawIdentifierWhitespace))
     return false;

validation-test/compiler_crashers_2/43bf2cb496111e.swift renamed to validation-test/compiler_crashers_2_fixed/43bf2cb496111e.swift

@@ -1,3 +1,3 @@
 // {"signature":"swift::Lexer::formEscapedIdentifierToken(char const*)"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 ``