Support for output message ranges, instead of just the position

[DevilXD]

Feature

Following the discussion in microsoft/vscode#142810, I propose MyPy to output a range over which a typing error occurs, instead of just the position of it. The current message with --show-column-numbers and --no-pretty looks like this:

test.py:4:5: error: Argument 1 to "foo" has incompatible type "str"; expected "int"

It'd be great if a range would be included for the column numbers, if possible:

test.py:4:5-15: error: Argument 1 to "foo" has incompatible type "str"; expected "int"

Output with --pretty could then use multiple ^ characters to visualize the range. Omitting --show-column-numbers wouldn't display column numbers at all, thus the output would remain unchanged.

Pitch

This change would allow the VSCode Python extension to output diagnostic objects with proper ranges, since the current implementation only underlines one character and makes it hard to work with, and other proposed solutions appear to be non-trivial at the very least.

[cdce8p]

Some implementation considerations:

• The end position should also contain a lineno in case the error stretches across multiple lines.
• Only Python 3.8 added the end_lineno and end_col_offset attributes to AST nodes. It might not be practical to support it for 3.7

[JelleZijlstra]

Agree that we should do this in Python versions where we have the right information in the AST.

[devmessias]

I can address that.
About the use of multiple ^ in my project (pyastrx-alpha) I did something similar, take a look

The range of code shown is controlled by other parameters (context). For colors, I'm using rich, but I believe that is not a good idea to add a dependency in mypy.

[97littleleaf11]

Closed by #13148