[Lexer] Factor out diagnostics for single-quoted string literal

For readability.

Author: rintaro

lib/Parse/Lexer.cpp

@@ -1737,6 +1737,51 @@ static void validateMultilineIndents(const Token &Str,
                                   commonIndentation);
 }
 
+/// Emit diagnostics for single-quote string and suggest replacement
+/// with double-quoted equivalent.
+static void diagnoseSingleQuoteStringLiteral(const char *TokStart,
+                                             const char *TokEnd,
+                                             DiagnosticEngine *D) {
+  assert(*TokStart == '\'' && TokEnd[-1] == '\'');
+  if (!D)
+    return;
+
+  SmallString<32> replacement;
+  replacement.push_back('"');
+  const char *Ptr = TokStart + 1;
+  const char *OutputPtr = Ptr;
+
+  while (*Ptr++ != '\'' && Ptr < TokEnd) {
+    if (Ptr[-1] == '\\') {
+      if (*Ptr == '\'') {
+        replacement.append(OutputPtr, Ptr - 1);
+        OutputPtr = Ptr + 1;
+        // Un-escape single quotes.
+        replacement.push_back('\'');
+      } else if (*Ptr == '(') {
+        // Preserve the contents of interpolation.
+        Ptr = skipToEndOfInterpolatedExpression(Ptr + 1, replacement.end(),
+                                                /*IsMultiline=*/false);
+        assert(*Ptr == ')');
+      }
+      // Skip over escaped characters.
+      ++Ptr;
+    } else if (Ptr[-1] == '"') {
+      replacement.append(OutputPtr, Ptr - 1);
+      OutputPtr = Ptr;
+      // Escape double quotes.
+      replacement.append("\\\"");
+    }
+  }
+  assert(Ptr == TokEnd && Ptr[-1] == '\'');
+  replacement.append(OutputPtr, Ptr - 1);
+  replacement.push_back('"');
+
+  D->diagnose(Lexer::getSourceLoc(TokStart), diag::lex_single_quote_string)
+      .fixItReplaceChars(Lexer::getSourceLoc(TokStart),
+                         Lexer::getSourceLoc(TokEnd), replacement);
+}
+
 /// lexStringLiteral:
 ///   string_literal ::= ["]([^"\\\n\r]|character_escape)*["]
 ///   string_literal ::= ["]["]["].*["]["]["] - approximately
@@ -1793,46 +1838,9 @@ void Lexer::lexStringLiteral(unsigned CustomDelimiterLen) {
   }
 
   if (QuoteChar == '\'') {
-    // Emit diagnostics for single-quote string and suggest replacement
-    // with double-quoted equivalent.
     assert(!IsMultilineString && CustomDelimiterLen == 0 &&
            "Single quoted string cannot have custom delimitor, nor multiline");
-    assert(*TokStart == '\'' && CurPtr[-1] == '\'');
-
-    SmallString<32> replacement;
-    replacement.push_back('"');
-    const char *Ptr = TokStart + 1;
-    const char *OutputPtr = Ptr;
-
-    while (*Ptr++ != '\'') {
-      if (Ptr[-1] == '\\') {
-        if (*Ptr == '\'') {
-          replacement.append(OutputPtr, Ptr - 1);
-          OutputPtr = Ptr + 1;
-          // Un-escape single quotes.
-          replacement.push_back('\'');
-        } else if (*Ptr == '(') {
-          // Preserve the contents of interpolation.
-          Ptr = skipToEndOfInterpolatedExpression(Ptr + 1, replacement.end(),
-                                                  /*IsMultiline=*/false);
-          assert(*Ptr == ')');
-        }
-        // Skip over escaped characters.
-        ++Ptr;
-      } else if (Ptr[-1] == '"') {
-        replacement.append(OutputPtr, Ptr - 1);
-        OutputPtr = Ptr;
-        // Escape double quotes.
-        replacement.append("\\\"");
-      }
-    }
-    assert(Ptr == CurPtr);
-    replacement.append(OutputPtr, Ptr - 1);
-    replacement.push_back('"');
-
-    diagnose(TokStart, diag::lex_single_quote_string)
-        .fixItReplaceChars(getSourceLoc(TokStart), getSourceLoc(CurPtr),
-                           replacement);
+    diagnoseSingleQuoteStringLiteral(TokStart, CurPtr, Diags);
   }
 
   if (wasErroneous)