Description

When using tab completion, if you press an arrow key to navigate, the current completion candidate is discarded, and the raw escape sequence characters (like [D, [C) are appended to the input buffer as literal text.

Steps to reproduce

// set completion callback
void CompletionTest(const char *, linenoiseCompletions *lc) {
  linenoiseAddCompletion(lc, "Text1");
}

int main() {
  linenoiseSetCompletionCallback(CompletionTest);
  /* ... loop ... */
}

1. Pressing Tab to trigger completion, the prompt shows the candidate Text1.
2. Pressing the Left Arrow key, the prompt becomes [D.
3. Inspecting the input line reveals that the underlying buffer data has also been replaced by [D.

> Text1 <- Shows candidate after pressing Tab
> [D    <- Becomes [D after pressing Left Arrow

Expected behavior

Arrow keys should be handled correctly during completion:

• The cursor should move in the specified direction.
• It should accept the current completion candidate.

Cause analysis

In linenoise.c, the completeLine function handles case 27 (ESC) by immediately setting ls->in_completion = 0 and returning c = 0.

It fails to check if the ESC character is the start of a multi-byte escape sequence. Consequently, the subsequent bytes (e.g., [D) are interpreted as user input in linenoiseEditFeed.

Proposed fix

Modify completeLine to check for escape sequences: When an ESC is received, attempt to read the next 2 bytes to determine if it is an arrow key sequence (similar to linenoiseEditFeed).

I think this modification wouldn't be too complicated. I'd be happy to submit a PR for this if the approach sounds good.