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rustfmt does not discover modules through cfg_select! #158371
Description
In case this issue is a better fit for the rustfmt repo, feel free to move it there. Also, if this is not a good fit for the regression tag, please change it.
Given this lib.rs and corresponding module files:
cfg_match! {
target_family = "unix" => {
mod format_me_please_1;
}
_ => {
mod format_me_please_2;
}
}When formatting this, everything is fine:
$ rustfmt src/lib.rs --verbose
Formatting src/format_me_please_1.rs
Formatting src/format_me_please_2.rs
Formatting src/lib.rs
Spent 0.004 secs in the parsing phase, and 0.002 secs in the formatting phaseSupport for detecting module files through cfg_match! was addded in rust-lang/rustfmt#6522. But cfg_match! was renamed to cfg_select! in #137198, and if you change the code above to say cfg_select!, it no longer detects the module files:
$ rustfmt src/lib.rs --verbose
Formatting src/lib.rs
Spent 0.002 secs in the parsing phase, and 0.001 secs in the formatting phaseSo anyone who has used cfg_select! to define modules in other files has possibly unformatted files. This is especially relevant due to the recent stabilization of cfg_select! (#149783) the migration from cfg_if! to cfg_select! in the ecosystem (e.g., rust-lang/compiler-builtins#1224).
#154202 does not appear to fix this issue. Renaming the corresponding occurrences in rustfmt fixes the issue for me, so I have opened #158372.
Activity
tgross35 commentedon Jun 24, 2026
Started a Zulip discussion #t-rustfmt > cfg_select module discovery
rustbot commentedon Jun 26, 2026
Assigning P-medium (discussion on Zulip).
Rollup merge of rust-lang#158372 - mkroening:rustfmt-cfg_select-modul…
Unrolled build for #158372
Rollup merge of #158372 - mkroening:rustfmt-cfg_select-modules, r=ytm…
Rollup merge of #158372 - mkroening:rustfmt-cfg_select-modules, r=ytm…