rust-project.json runnable filtering always selects the first `Run` runnable

[lukasoyen]

The filtering of bin runnables from the rust-project.json always selects the first Run runnable. In a project with a lot of runnables, this breaks the Run / Debug integration in VSCode.

rust-analyzer version: 3d2c40d705f5663fccf4a4d89ea457876ac32df6 (2025-08-11)

• In target_spec_for_crate() runnables are copied over instead of selected by current crate / build info. This is one place where filtering could be expected.
• In runnable_args() the first RunnableKind::Run is selected. This is another place where filtering could be expected.

Related:

• better testing support for rust-project.json #20359
• fix: project json runnable kind bin substitution #20396 (with this PR the rust-project.json generation could be simplified. Though the filtering bug would still be present.)

[lukasoyen]

The difficulty is in selecting the correct runnable. There is nothing that ties the build info to the runnables. And inspecting the args of a runnable seems to be too fragile.

[lukasoyen]

I guess one option would be to augment runnable_fn() and RunnableKind::Bin to return back the build.label if available. The filtering could then make use of that.