Bug report

On second thought this issue should be an enhancement instead of a bug report. Sorry for the wrong template.

Bug description:

There are some cases where_pyrepl auto-indentation works not well.

Cases

1. A line ending with: in a multi-line string is wrongly indented.

Observed

>>> s ='''... Note:... ␣␣␣␣|

Expected

>>> s ='''... Note:... |

2. # inside strings is seen as a comment, the following: is ignored.

Observed

>>>if'' =='#':...|

Expected

>>>if'' =='#':... ␣␣␣␣|

3. When the entire cursor line is a comment and is already indented, pressing Enter gives a further indent.

Observed

>>> deff():...# foo⤶... ␣␣␣␣␣␣␣␣|

Expected

>>> deff():...# foo⤶... ␣␣␣␣|

Possible solution

Currently_should_auto_indent() parses thebuffer fromright to left and ends at the first newline it encounters. Only the last line that is not a comment line of thebuffer is parsed.

But by parsing fromright to left we can't tell if a# starts a comment or is part of a string. For example if we see a" first and then a#, we don't know if the# is a comment. To know that, we need to know if the" is a string boundary, but the# might comment out the", so we can't be sure. There is a information dependency cycle.

To fix this I made achange to parse thebuffer fromleft to right, keeping track of whether current char is inside a string or a comment. This approach solves the above three cases. However the wholebuffer is parsed on every call of_should_auto_indent(), with very long buffer, there might be noticeable delay when pressing Enter.

This is a big change. It affects how_should_auto_indent() works as a whole. I am hesitated to create a PR and just put it here first to hopefully get feedback.

CPython versions tested on:

3.15

Operating systems tested on:

Linux