bootstrap: Make `main.rs` a stub that calls into the library crate by Zalathar · Pull Request #160829 · rust-lang/rust

Zalathar · 2026-08-10T03:22:12Z

As with some other bootstrap tools (e.g. compiletest), bootstrap itself is built as a small binary crate (executable) that links to a larger library crate.

If there is non-trivial code in main.rs, then any items it touches need to be publicly exported from the library crate. Those public exports make it harder to identify unused code within bootstrap.

As far as I can tell, there is no compelling rule or principle that determines whether code should be in the entry point or in the library crate, other than historical inertia.

This PR therefore takes all of the code from main.rs, and moves it into a new file cli_main.rs within the bootstrap library crate. That avoids the need for any public exports other than cli_main::main itself.

There should be no change to bootstrap behaviour.

This change makes it possible to change all of bootstrap's pub items to pub(crate). That migration is left to a future PR, as it involves a fair bit of churn, and requires decisions on how to deal with pub items that are currently unused.

Prior art:

compiletest: Isolate public APIs and minimize public surface area #147506

rustbot · 2026-08-10T03:22:18Z

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Kobzol · 2026-08-10T07:47:40Z

I would really like for rustc/Cargo to have a way of identifying unused pub items in libraries 😢 Marking everything with pub(crate) is annoying.

In fact, since rustc can now (AFAIK) detect unused pub in binaries, I wonder if we should do the opposite, and turn the whole of bootstrap from a library to a single binary, and reduce one Cargo compilation target 😆 Though we'd still need unit tests.

Zalathar · 2026-08-10T08:03:52Z

IMO, trying to use pub as a shorthand for pub(crate) (but only if you happen to remember that you're in a binary crate) is more trouble than it's worth.

Consistently using pub(crate) for anything that doesn't strictly need to be pub is much easier to reason about.

clubby789 · 2026-08-10T15:51:42Z

@bors r+

rust-bors · 2026-08-10T15:51:45Z

📌 Commit 85b2700 has been approved by clubby789

It is now in the queue for this repository.

…uwer Rollup of 9 pull requests Successful merges: - #158404 (trait_solver: normalize next-gen region constraints) - #160631 (Do not eagerly download rustfmt in bootstrap) - #160642 (mir: prohibit projection into scalable vec) - #160749 (MaybeDangling: ensure references fit inside the address space) - #160791 (Use recognizer functions for enums and tuple structs) - #160500 (Fix inaccurate description for crate and pathroot) - #160590 (Docs & bors: Replace mentions of libs-api with libs) - #160825 (Fix references to unsupported on sys::paths::unix) - #160852 (Use `remove_dir_all` for `./x clean`) Failed merges: - #160829 (bootstrap: Make `main.rs` a stub that calls into the library crate)

This intermediate commit helps to preserve line history.

If there is non-trivial code in `main.rs`, then any items it touches need to be publicly exported from the library crate. Those public exports make it harder to identify unused code within bootstrap.

There is no need to re-export anything, so all `pub use` imports can be simplified to `use` and merged with their siblings.

rustbot · 2026-08-11T01:50:49Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

Zalathar · 2026-08-11T05:10:05Z

Rebased over import conflicts.

@bors r=clubby789

rust-bors · 2026-08-11T05:10:08Z

📌 Commit 55050c1 has been approved by clubby789

It is now in the queue for this repository.

…uwer Rollup of 5 pull requests Successful merges: - #156338 (Implement derives for Reborrow and CoerceShared) - #158083 (Fix perf regression in `Read::read_to_end` on short reads due to not checking if the cursor has initialized bytes) - #160829 (bootstrap: Make `main.rs` a stub that calls into the library crate) - #159839 (point at closure return expression in non-`FnOnce` E0271 errors) - #160775 (interpret: treat pattern and unsafe-binder as ABI-transparent)

Rollup merge of #160829 - Zalathar:bootstrap-main, r=clubby789 bootstrap: Make `main.rs` a stub that calls into the library crate As with some other bootstrap tools (e.g. compiletest), bootstrap itself is built as a small binary crate (executable) that links to a larger library crate. If there is non-trivial code in `main.rs`, then any items it touches need to be publicly exported from the library crate. Those public exports make it harder to identify unused code within bootstrap. As far as I can tell, there is no compelling rule or principle that determines whether code should be in the entry point or in the library crate, other than historical inertia. This PR therefore takes all of the code from `main.rs`, and moves it into a new file `cli_main.rs` within the bootstrap library crate. That avoids the need for any public exports other than `cli_main::main` itself. There should be no change to bootstrap behaviour. --- This change makes it possible to change all of bootstrap's `pub` items to `pub(crate)`. That migration is left to a future PR, as it involves a fair bit of churn, and requires decisions on how to deal with pub items that are currently unused. Prior art: - #147506

…uwer Rollup of 9 pull requests Successful merges: - rust-lang/rust#158404 (trait_solver: normalize next-gen region constraints) - rust-lang/rust#160631 (Do not eagerly download rustfmt in bootstrap) - rust-lang/rust#160642 (mir: prohibit projection into scalable vec) - rust-lang/rust#160749 (MaybeDangling: ensure references fit inside the address space) - rust-lang/rust#160791 (Use recognizer functions for enums and tuple structs) - rust-lang/rust#160500 (Fix inaccurate description for crate and pathroot) - rust-lang/rust#160590 (Docs & bors: Replace mentions of libs-api with libs) - rust-lang/rust#160825 (Fix references to unsupported on sys::paths::unix) - rust-lang/rust#160852 (Use `remove_dir_all` for `./x clean`) Failed merges: - rust-lang/rust#160829 (bootstrap: Make `main.rs` a stub that calls into the library crate)

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels Aug 10, 2026

rustbot assigned clubby789 Aug 10, 2026

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 10, 2026

This was referenced Aug 10, 2026

Rollup of 9 pull requests #160863

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Rollup of 9 pull requests #160867

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rust-bors Bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 10, 2026

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Zalathar added 3 commits August 11, 2026 11:45

Move and rename bootstrap's main.rs

b189f6e

This intermediate commit helps to preserve line history.

Make bootstrap's main.rs a stub that calls into the library crate

d14e7c4

If there is non-trivial code in `main.rs`, then any items it touches need to be publicly exported from the library crate. Those public exports make it harder to identify unused code within bootstrap.

Tidy imports in lib.rs

55050c1

There is no need to re-export anything, so all `pub use` imports can be simplified to `use` and merged with their siblings.

Zalathar force-pushed the bootstrap-main branch from 85b2700 to 55050c1 Compare August 11, 2026 01:50

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 11, 2026

JonathanBrouwer mentioned this pull request Aug 11, 2026

Rollup of 5 pull requests #160899

Merged

rust-bors Bot merged commit 6a1d74f into rust-lang:main Aug 11, 2026
13 checks passed

rustbot added this to the 1.99.0 milestone Aug 11, 2026

Zalathar deleted the bootstrap-main branch August 11, 2026 14:00

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bootstrap: Make `main.rs` a stub that calls into the library crate - #160829

bootstrap: Make `main.rs` a stub that calls into the library crate#160829
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