Respect TERM=dumb for cursor position queries

[catlover-bot]

Summary

Respect TERM=dumb when Reedline queries the terminal for the cursor position.

TERM=dumb does not provide cursor-position reporting, but Painter currently calls crossterm::cursor::position() from several paths. In particular, initialize_prompt_position() propagates a failed query directly.

This PR centralizes cursor-position queries behind a small wrapper:

• when TERM=dumb, skip cursor::position() and return no measured position
• otherwise preserve the existing Crossterm behavior
• read TERM for each query rather than caching it, so runtime changes to TERM are respected
• use the painter's existing cached/count-based fallback when no cursor position is available

TERM=dumb also disables ANSI coloring while preserving the configured with_ansi_colors value. TERM is read dynamically, so runtime changes are respected for both cursor-position queries and ANSI output.

Testing

• regression tests for the TERM=dumb cursor-position path
• ANSI-policy tests for TERM=dumb, regular terminals, and an unset TERM
• full test suite with all features
• cargo clippy --locked --all-targets --all-features -- -D warnings
• git diff --check

Fixes #1009

[fdncred]

I wonder if it's worth centralizing all interactions with the env in calls like std::env::var_os("TERM");? It may be nice to have one function to rule them all since dealing with the env isn't threadsafe. Thoughts?

[catlover-bot]

That makes sense to me.

I checked the current codebase and found only three direct process environment-variable reads: TERM, USERPROFILE, and HOME, so the scope is small enough to centralize here.

I pushed a follow-up commit that routes those reads through a single utils::environment::var_os helper. I left APIs such as current_dir() out since those are process-state operations rather than environment-variable reads.

One nuance is that the wrapper itself does not make concurrent external environment mutation thread-safe. The benefit is that Reedline now has one place where a future synchronization or snapshot policy can be implemented instead of having environment-variable reads scattered around the crate.

The full library tests and clippy are still green after the refactor.

[fdncred]

The benefit is that Reedline now has one place where a future synchronization or snapshot policy can be implemented instead of having environment-variable reads scattered around the crate.

yup, that's exactly what I was asking.

Thanks for the update. We'll wait to see what @kronberger-droid thinks. I'm not sure it's a regression so I doubt this will be for the upcoming patch.

[kronberger-droid]

Definitely not a regression, thats a longstanding issue.
I would not rush it in before the patch.

I will take a closer look tomorrow.

[catlover-bot]

Thanks!

[kronberger-droid]

Well I think it would make sense to thread in the ansi-coloring removal here to.
It should be easy enough since we already handle it consistently through the config.

[catlover-bot]

Thanks, I threaded TERM=dumb through the existing ANSI-color configuration as well.

The configured with_ansi_colors value is preserved, while the effective value is disabled when the current TERM is dumb. I compute that effective value once per paint operation, so the same render uses a consistent setting while later runtime changes to TERM are still respected.

I also rebased onto current main and kept the newer W::cursor_position() abstraction, so non-dumb terminals continue through the existing testable terminal-I/O path.

I added coverage for TERM=dumb, a regular terminal, and an unset TERM; the full test suite and clippy are green.