[Lexer] Improve fix-it to remove "too long" delimiter in string literal

Fix-it to remove extra '#'s at once.

Author: rintaro

lib/Parse/Lexer.cpp

@@ -1277,16 +1277,20 @@ static bool delimiterMatches(unsigned CustomDelimiterLen, const char *&BytesPtr,
   if (!CustomDelimiterLen)
     return true;
   const char *TmpPtr = BytesPtr;
-  while (CustomDelimiterLen--)
-    if (!diagnoseZeroWidthMatchAndAdvance('#', TmpPtr, Diags))
-      return false;
-  BytesPtr = TmpPtr;
-  if (*BytesPtr == '#' && Diags)
-    Diags->diagnose(Lexer::getSourceLoc(BytesPtr), IsClosing ?
-                    diag::lex_invalid_closing_delimiter :
-                    diag::lex_invalid_escape_delimiter)
-      .fixItRemoveChars(Lexer::getSourceLoc(BytesPtr),
-                        Lexer::getSourceLoc(BytesPtr + 1));
+  while (diagnoseZeroWidthMatchAndAdvance('#', TmpPtr, Diags)) {}
+
+  if (TmpPtr - BytesPtr < CustomDelimiterLen)
+    return false;
+
+  BytesPtr += CustomDelimiterLen;
+
+  if (Diags && TmpPtr > BytesPtr) {
+    Diag<> message = IsClosing ? diag::lex_invalid_closing_delimiter
+                               : diag::lex_invalid_escape_delimiter;
+    Diags->diagnose(Lexer::getSourceLoc(BytesPtr), message)
+        .fixItRemoveChars(Lexer::getSourceLoc(BytesPtr),
+                          Lexer::getSourceLoc(TmpPtr));
+  }
   return true;
 }
 

test/Parse/raw_string_errors.swift

@@ -12,7 +12,7 @@ let _ = #"\##("invalid")"#
 let _ = ####"invalid"###
 // expected-error@-1{{unterminated string literal}}
 
-let _ = ###"invalid"####
-// expected-error@-1{{too many '#' characters in closing delimiter}}
+let _ = ###"invalid"######
+// expected-error@-1{{too many '#' characters in closing delimiter}}{{24-27=}}
 // expected-error@-2{{consecutive statements on a line must be separated by ';'}}
 // expected-error@-3{{expected expression}}