History and backspace corrupt commandline

[sophiajt]

With the latest rustyline, if you do the following steps, you get a corrupted input line. You can repro this using the same app

cargo run --example example

Next, type something into one line:

1> this is a test file
Line: this is a test file

Next, press up, to get to the previous line, move the arrow to get to the word test and backspace to delete it.

This is what it looks like when I do this:

Notice the line is now corrupted and is showing both the editing line and something from the previous history of the line.

[gwenn]

The highlighted/bold text is the suggestion/hint based on history.
The current implementation does not check if the cursor is at the end of the line / if the whole line matches a previous history entry.
https://github.com/kkawakam/rustyline/blob/master/src/hint.rs#L37

    fn hint(&self, line: &str, pos: usize, ctx: &Context<'_>) -> Option<String> {
...
        if let Some(history_index) =
            ctx.history
                .starts_with(&line[..pos], start, Direction::Reverse)
...

[gwenn]

liner does not display any suggestion while editing an history entry:
https://github.com/redox-os/liner/blob/master/src/editor.rs#L863

        // If we are editing a previous history item no autosuggestion.
        if self.hist_buf_valid {
            return None;
        }

[gwenn]

See #240

[sophiajt]

That fix works for me, thanks!