[Parse] Fix buffer overrun in advanceIfMultilineDelimiter

[hamishknight]

Make sure we don't scan off the end of the buffer, and scan for the delimiter before attempting the lookahead.

rdar://165774720

[hamishknight]

@swift-ci please test

[hamishknight]

@swift-ci please SourceKit stress test

[rintaro]

No check for EndPtr because we guarantee *EndPtr is 0?
But maybe we could early check like:

if (CurPtr + 2 >= EndPtr) return false;

[hamishknight]

Yeah exactly, e.g delimiterMatches does

  while (diagnoseZeroWidthMatchAndAdvance('#', TmpPtr, Diags)) {}

I don't mind adding an extra check though

[rintaro]

I see. Considering delimiterMatches does that, I don't think extra check is needed.

[rintaro]

scanDelimiter is used only once. Why not

const char *DelimEnd = nullptr;
{
    // CurPtr here points to the character after `"`.
    const char *TmpPtr = CurPtr;
    if (*(TmpPtr - 1) == '"' &&
        diagnoseZeroWidthMatchAndAdvance('"', TmpPtr, Diags) &&
        diagnoseZeroWidthMatchAndAdvance('"', TmpPtr, Diags)) {
      DelimEnd = TmpPtr;
    } else {
      return false;
    }
}

If it's just a matter of the code style, I'm fine with the lambda.

[hamishknight]

Yeah personally I prefer the lambda, shame C++ doesn't have guard statements 😄

[rintaro]

Or just like swift-syntax counterpart

// CurPtr here points to the character after `"`.
const char *DelimEnd = CurPtr;
if (*(DelimEnd - 1) == '"' &&
    diagnoseZeroWidthMatchAndAdvance('"', DelimEnd, Diags) &&
    diagnoseZeroWidthMatchAndAdvance('"', DelimEnd, Diags)) {
 // Found the delimiter
} else {
  return false;
}

[hamishknight]

An empty if body feels weird to me, I don't mind changing it though

[rintaro]

Okay. I'm fine with as-is