Change "error finalizing incremental compilation" text and emit it as a note, not a warning by lambdageek · Pull Request #154110 · rust-lang/rust

lambdageek · 2026-03-19T18:49:10Z

As mentioned in #151181 (comment) and #151181 (comment) the current message could be improved:

Right now it displays as "warning: error ..." which is confusing (is it an error or a warning)
It doesn't give the user a clear indication of what the consequences are
The current build is successful. The next build might be slower

The new message is now

note: did not finalize incremental compilation session directory ...
  |
  = help: the next build will not be able to reuse work from this compilation

I started a zulip thread #t-compiler/incremental > Ergonomics of "error finalizing incremental session"

The warning has no error code, so in a `-D warnings` environment, it's impossible to ignore if it consistently breaks your build. Change it to a note so it is still visible, but doesn't break the build

Remove the confusing word "error". The diagnostic is already prefixed with a level when it is displayed, so this is redundant and possibly confusing ("warning: error ..."). Add some help text summarizing the impact of what happened: the next build won't be able to reuse work from the current run.

rustbot · 2026-03-19T19:52:25Z

r? @wesleywiser

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Kivooeo · 2026-03-19T23:09:06Z

I like new wording, but I'm wondering if that's possible to add a test for this?

lambdageek · 2026-03-20T01:58:02Z

I like new wording, but I'm wondering if that's possible to add a test for this?

Came up with a convoluted way to test this. Make a proc macro that poisons the incremental -working directory in a way that would make the rename operation in finalize_session_directory fail. The proc macro runs when the incremental session directory already exists but before the session is finalized, so it can mess with it.

On Unix, change permissions on the parent directory of the -working directory to read-only
On Windows, write a file into the -working directory and leak the handle

I'm not sure this a great idea

I'll push it to the PR, though

…e fail Use a proc macro to observe the incremental session directory and do something platform specific so that renaming the '-working' session directory during finalize_session_directory will fail. On Unix, change the permissions on the parent directory to be read-only. On Windows, open and leak a file inside the `-working` directory.

wesleywiser · 2026-03-26T18:01:49Z

compiler/rustc_incremental/src/errors.rs

 #[derive(Diagnostic)]
-#[diag("error finalizing incremental compilation session directory `{$path}`: {$err}")]
+#[diag("did not finalize incremental compilation session directory `{$path}`: {$err}")]
+#[help("the next build will not be able to reuse work from this compilation")]


I like that this focuses the issue directly on the impact the user might care about 👍

wesleywiser · 2026-03-26T18:02:59Z

@bors r+ rollup

rust-bors · 2026-03-26T18:03:03Z

📌 Commit 0cc4946 has been approved by wesleywiser

It is now in the queue for this repository.

…r=wesleywiser Change "error finalizing incremental compilation" text and emit it as a note, not a warning As mentioned in rust-lang#151181 (comment) and rust-lang#151181 (comment) the current message could be improved: 1. Right now it displays as "warning: error ..." which is confusing (is it an error or a warning) 2. It doesn't give the user a clear indication of what the consequences are 3. The _current_ build is successful. The _next_ build might be slower The new message is now ```text note: did not finalize incremental compilation session directory ... | = help: the next build will not be able to reuse work from this compilation ``` I started a zulip thread [#t-compiler/incremental > Ergonomics of "error finalizing incremental session"](https://rust-lang.zulipchat.com/#narrow/channel/241847-t-compiler.2Fincremental/topic/Ergonomics.20of.20.22error.20finalizing.20incremental.20session.22/with/580191447)

Rollup of 7 pull requests Successful merges: - #152457 (Pass -pg to linker when using -Zinstrument-mcount) - #154031 (Remove divergence check from check_expr_array) - #154418 (move many tests out of `ui/unsafe`) - #153662 (Suggest fully qualified path on method name collision) - #153675 (simd_add/sub/mul/neg: document overflow behavior) - #154110 (Change "error finalizing incremental compilation" text and emit it as a note, not a warning) - #154430 (Create GPU target notification group)

Zalathar · 2026-03-27T02:19:00Z

Failed in rollup: Rollup of 7 pull requests #154440 (comment)

@bors r-

rust-bors · 2026-03-27T02:19:05Z

This pull request was unapproved.

This PR was contained in a rollup (#154440), which was unapproved.

lambdageek · 2026-03-27T11:37:57Z

ok, #154440 (comment) makes sense: we need the proc macro compiled for the host platform, not the target.

need to figure out how to do that (or skip the test everywhere except normal unix & windows)
need to run some tests for interesting platforms here in the PR before it goes into the queue

The test needs proc-macros to function

lambdageek · 2026-03-27T14:49:35Z

@bors try jobs=test-various

rust-bors · 2026-03-27T14:49:38Z

@lambdageek: 🔑 Insufficient privileges: not in try users

lambdageek · 2026-03-27T14:53:01Z

@wesleywiser PTAL (and re-run "test-various"?)

Kivooeo · 2026-03-27T17:59:43Z

@bors try jobs=test-various

Change "error finalizing incremental compilation" text and emit it as a note, not a warning try-job: test-various

rust-bors · 2026-03-27T20:06:42Z

☀️ Try build successful (CI)
Build commit: 2f749ba (2f749bad253f070dba5f0b67caf5911659c402b9, parent: fda6d37bb88ee12fd50fa54d15859f1f91b74f55)

wesleywiser · 2026-03-27T21:27:09Z

@bors r+

rust-bors · 2026-03-27T21:27:12Z

📌 Commit 0c05f6c has been approved by wesleywiser

It is now in the queue for this repository.

Rollup of 9 pull requests Successful merges: - #154357 (uefi: extend comment for TcpStream Send impl) - #154410 (Clean up the API for opening/checking incremental-compilation files ) - #154081 (format safety doc of Rc/Arc::from_raw/from_raw_in) - #154110 (Change "error finalizing incremental compilation" text and emit it as a note, not a warning) - #154196 (Make `Ipv6Addr::multicast_scope()` exhaustive) - #154221 (`vec::as_mut_slice()`: use lowercase "isize" in safety comment) - #154234 (Use common Timestamp impl in Hermit (attempt 2)) - #154396 (chore(deps): update rust crate tar to v0.4.45) - #154488 (Revert "Unstable book options parser")

Rollup merge of #154110 - lambdageek:fix/incr-compile-note, r=wesleywiser Change "error finalizing incremental compilation" text and emit it as a note, not a warning As mentioned in #151181 (comment) and #151181 (comment) the current message could be improved: 1. Right now it displays as "warning: error ..." which is confusing (is it an error or a warning) 2. It doesn't give the user a clear indication of what the consequences are 3. The _current_ build is successful. The _next_ build might be slower The new message is now ```text note: did not finalize incremental compilation session directory ... | = help: the next build will not be able to reuse work from this compilation ``` I started a zulip thread [#t-compiler/incremental > Ergonomics of "error finalizing incremental session"](https://rust-lang.zulipchat.com/#narrow/channel/241847-t-compiler.2Fincremental/topic/Ergonomics.20of.20.22error.20finalizing.20incremental.20session.22/with/580191447)

Zalathar · 2026-03-29T10:39:32Z

The newly-added run-make test works very hard to trigger a real rename failure, via a custom proc-macro and some platform-specific code.

But for the sake of testing diagnostics I wonder if it might have been more appropriate to instead add a perma-unstable compiler flag that simply fakes an error in the appropriate place.

Kivooeo · 2026-03-29T10:44:33Z

By the way, I originally asked for the test to be added just to see this diagnostic in action. However, looking at the test, I can't see any output, such as .stderr. How is this test testing this diagnostic?

Zalathar · 2026-03-29T11:01:14Z

Looks like there are some hardcoded non-blessable assertions in rmake.rs.

lambdageek added 2 commits March 13, 2026 14:37

change "error finalizing incremental compilation" from warning to note

384f363

The warning has no error code, so in a `-D warnings` environment, it's impossible to ignore if it consistently breaks your build. Change it to a note so it is still visible, but doesn't break the build

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Mar 19, 2026

lambdageek marked this pull request as ready for review March 19, 2026 19:52

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 19, 2026

rustbot assigned wesleywiser Mar 19, 2026

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Mar 19, 2026

rustbot added the A-run-make Area: port run-make Makefiles to rmake.rs label Mar 20, 2026

lambdageek force-pushed the fix/incr-compile-note branch from 525cb88 to 0cc4946 Compare March 20, 2026 02:37

wesleywiser approved these changes Mar 26, 2026

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JonathanBrouwer mentioned this pull request Mar 26, 2026

Rollup of 9 pull requests #154438

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matthiaskrgr mentioned this pull request Mar 26, 2026

Rollup of 7 pull requests #154440

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Add ignore-cross-compile to incremental-finalize-fail

0c05f6c

The test needs proc-macros to function

rust-bors bot pushed a commit that referenced this pull request Mar 27, 2026

Auto merge of #154110 - lambdageek:fix/incr-compile-note, r=<try>

2f749ba

Change "error finalizing incremental compilation" text and emit it as a note, not a warning try-job: test-various

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Zalathar mentioned this pull request Mar 28, 2026

Rollup of 9 pull requests #154489

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lambdageek deleted the fix/incr-compile-note branch March 28, 2026 11:51

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