fix(log): emit fingeprint log also for no-rebuild unit by weihanglo · Pull Request #16408 · rust-lang/cargo

weihanglo · 2025-12-17T04:56:40Z

What does this PR try to resolve?

This makes the log message more complete.
Also consumers can check whether a crate is really "no rebuild needed"

It also open a door if we want to log the current fingerprint value.

Part of #15844.

How to test and review this PR?

The test diff should show the behavior change

Consumer can reference to unit-registered event for details

rustbot · 2025-12-17T04:56:45Z

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epage · 2025-12-17T14:02:13Z

+            }
+            None => util::log_message::FingerprintStatus::Fresh,
+        };
+        logger.log(LogMessage::UnitFingerprint {


It isn't too clear to me why this is needed if we know what all the build units are, then the assumption if there isn't a rebuild reason then it wasn't rebuilt.

It was kinda a path towards recording previous builds. Even without 8bf836a, it is still useful if we start logging fingerprint value itself (which I was working towards but realized that capturing fs_status might be a bit tricky that we can't never get a useful diff from two fingerprints.)

The idea came from #t-cargo > build analysis log format @ 💬

What I'm wondering about is recording the values that were diffed so the user can do arbitrary diffs

In the fingerprint directory, we have a json file and I was wondering if we could replace that json file with one or more messages

e.g.

{"rustc":5092870430032522185,"features":"[]","declared_features":"[]","target":2199929927738793367,"profile":2241668132362809309,"path":10763286916239946207,"deps":[],"local":[{"CheckDepInfo":{"dep_info":"debug/build/foo/58363037c0a1f1bb/fingerprint/dep-lib-foo","checksum":false}}],"rustflags":[],"config":2069994364910194474,"compile_kind":0}

Well, either way, we can experiment and decide what we want as we work towards stabilization.

Yeah that was also what I was wondering, but then

Some information is kinda duplicate or can be derived from in other log messages.

The complete file system status and environment status were not captured. The fingerprint is still a comparison result of them, unable to diff.

Information there are hashes, which makes diffing less interesting (like, "this build is dirty because target file path changed from 10763286916 to src/foo/lib.rs"). And that's the reason previous_run_id was introduced.

It was hard to determine what is the minimal set of stable JSON schema we want to expose. We just don't provide a stable one, and instead emit an opaque JSON string.

Anyway, I think we're going to track a mix of diffable data and diffing results regardlessly.

This makes the log message more complete. Also consumers can check whether a crate is really "no rebuild needed" It also open a door if we want to log the current fingerprint value.

Update cargo submodule 13 commits in e91b2baa632c0c7e84216c91ecfe107c37d887c1..3861f60f6b58f57524c0e7aab1f5c1ad83e35409 2025-12-13 16:29:21 +0000 to 2025-12-19 21:53:33 +0000 - fix(sbom): Don't set CARGO_SBOM_PATH when empty (like stable) (rust-lang/cargo#16419) - chore(ci): report-timings to upload HTML report (rust-lang/cargo#16416) - fix(report): get the same feature parity of `--timings` (rust-lang/cargo#16414) - fix(docs): Document the only possible values for DEBUG in build scripts (rust-lang/cargo#16413) - fix(log): emit fingeprint log also for no-rebuild unit (rust-lang/cargo#16408) - Fix link to `doc_cfg` docs in cargo book (rust-lang/cargo#16404) - Add best pratice for how to check in generated files (rust-lang/cargo#16405) - test: Use a larger default term width (rust-lang/cargo#16403) - Document more services and permissions of the cargo team (rust-lang/cargo#16402) - fix(new): Improve quality of package name error messages (rust-lang/cargo#16398) - feat(log): add more log events (rust-lang/cargo#16390) - chore: bump to 0.95.0; update changelog (rust-lang/cargo#16395) - Cache submodule into git db (rust-lang/cargo#16246) r? ghost

Update cargo submodule 17 commits in e91b2baa632c0c7e84216c91ecfe107c37d887c1..94c368ad2b9db0f0da5bdd8421cea13786ce4412 2025-12-13 16:29:21 +0000 to 2025-12-26 19:39:15 +0000 - fix(vendor): unpack from local-registry cache path (rust-lang/cargo#16435) - feat(index): Stabilize pubtime (rust-lang/cargo#16372) - Experiment: Render timing pipeline in SVG (rust-lang/cargo#15091) - chore(triagebot): auto-label `Command-report` (rust-lang/cargo#16429) - fix(sbom): Don't set CARGO_SBOM_PATH when empty (like stable) (rust-lang/cargo#16419) - chore(ci): report-timings to upload HTML report (rust-lang/cargo#16416) - fix(report): get the same feature parity of `--timings` (rust-lang/cargo#16414) - fix(docs): Document the only possible values for DEBUG in build scripts (rust-lang/cargo#16413) - fix(log): emit fingeprint log also for no-rebuild unit (rust-lang/cargo#16408) - Fix link to `doc_cfg` docs in cargo book (rust-lang/cargo#16404) - Add best pratice for how to check in generated files (rust-lang/cargo#16405) - test: Use a larger default term width (rust-lang/cargo#16403) - Document more services and permissions of the cargo team (rust-lang/cargo#16402) - fix(new): Improve quality of package name error messages (rust-lang/cargo#16398) - feat(log): add more log events (rust-lang/cargo#16390) - chore: bump to 0.95.0; update changelog (rust-lang/cargo#16395) - Cache submodule into git db (rust-lang/cargo#16246) r? ghost

Update cargo submodule 13 commits in e91b2baa632c0c7e84216c91ecfe107c37d887c1..3861f60f6b58f57524c0e7aab1f5c1ad83e35409 2025-12-13 16:29:21 +0000 to 2025-12-19 21:53:33 +0000 - fix(sbom): Don't set CARGO_SBOM_PATH when empty (like stable) (rust-lang/cargo#16419) - chore(ci): report-timings to upload HTML report (rust-lang/cargo#16416) - fix(report): get the same feature parity of `--timings` (rust-lang/cargo#16414) - fix(docs): Document the only possible values for DEBUG in build scripts (rust-lang/cargo#16413) - fix(log): emit fingeprint log also for no-rebuild unit (rust-lang/cargo#16408) - Fix link to `doc_cfg` docs in cargo book (rust-lang/cargo#16404) - Add best pratice for how to check in generated files (rust-lang/cargo#16405) - test: Use a larger default term width (rust-lang/cargo#16403) - Document more services and permissions of the cargo team (rust-lang/cargo#16402) - fix(new): Improve quality of package name error messages (rust-lang/cargo#16398) - feat(log): add more log events (rust-lang/cargo#16390) - chore: bump to 0.95.0; update changelog (rust-lang/cargo#16395) - Cache submodule into git db (rust-lang/cargo#16246) r? ghost

Update cargo submodule 17 commits in e91b2baa632c0c7e84216c91ecfe107c37d887c1..94c368ad2b9db0f0da5bdd8421cea13786ce4412 2025-12-13 16:29:21 +0000 to 2025-12-26 19:39:15 +0000 - fix(vendor): unpack from local-registry cache path (rust-lang/cargo#16435) - feat(index): Stabilize pubtime (rust-lang/cargo#16372) - Experiment: Render timing pipeline in SVG (rust-lang/cargo#15091) - chore(triagebot): auto-label `Command-report` (rust-lang/cargo#16429) - fix(sbom): Don't set CARGO_SBOM_PATH when empty (like stable) (rust-lang/cargo#16419) - chore(ci): report-timings to upload HTML report (rust-lang/cargo#16416) - fix(report): get the same feature parity of `--timings` (rust-lang/cargo#16414) - fix(docs): Document the only possible values for DEBUG in build scripts (rust-lang/cargo#16413) - fix(log): emit fingeprint log also for no-rebuild unit (rust-lang/cargo#16408) - Fix link to `doc_cfg` docs in cargo book (rust-lang/cargo#16404) - Add best pratice for how to check in generated files (rust-lang/cargo#16405) - test: Use a larger default term width (rust-lang/cargo#16403) - Document more services and permissions of the cargo team (rust-lang/cargo#16402) - fix(new): Improve quality of package name error messages (rust-lang/cargo#16398) - feat(log): add more log events (rust-lang/cargo#16390) - chore: bump to 0.95.0; update changelog (rust-lang/cargo#16395) - Cache submodule into git db (rust-lang/cargo#16246) r? ghost

weihanglo added 3 commits December 16, 2025 20:44

fix(log): migrate rebuild message to unit index

0bb662b

Consumer can reference to unit-registered event for details

refactor(log): fingerprint comparison result in enum

5cdc66d

test(log): also enable build-analysis for first builds

371a9be

rustbot assigned epage Dec 17, 2025

rustbot added A-rebuild-detection Area: rebuild detection and fingerprinting S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 17, 2025

weihanglo added the Z-build-analysis Nightly: build-analysis label Dec 17, 2025

weihanglo mentioned this pull request Dec 17, 2025

Tracking Issue for -Zbuild-analysis #15844

Open

25 tasks

epage reviewed Dec 17, 2025

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Comment thread src/cargo/core/compiler/fingerprint/mod.rs Outdated

weihanglo force-pushed the rebuild branch 2 times, most recently from 2b5fb8b to 25c5e7c Compare December 17, 2025 14:52

fix(log): emit fingeprint log also for no-rebuild unit

32de338

This makes the log message more complete. Also consumers can check whether a crate is really "no rebuild needed" It also open a door if we want to log the current fingerprint value.

weihanglo force-pushed the rebuild branch from 25c5e7c to 32de338 Compare December 17, 2025 14:52

weihanglo changed the title ~~fix(log): add cross-session fingerprint tracking~~ fix(log): emit fingeprint log also for no-rebuild unit Dec 17, 2025

epage approved these changes Dec 17, 2025

View reviewed changes

epage enabled auto-merge December 17, 2025 20:11

epage added this pull request to the merge queue Dec 17, 2025

Merged via the queue into rust-lang:master with commit d8fc14a Dec 17, 2025
54 of 56 checks passed

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 17, 2025

weihanglo deleted the rebuild branch December 17, 2025 22:12

weihanglo mentioned this pull request Dec 20, 2025

Update cargo submodule rust-lang/rust#150181

Merged

rustbot added this to the 1.94.0 milestone Dec 20, 2025

This was referenced Dec 26, 2025

Prototype Cargo build analysis rust-lang/rust-project-goals#398

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Update cargo submodule rust-lang/rust#150421

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fix(log): emit fingeprint log also for no-rebuild unit#16408

fix(log): emit fingeprint log also for no-rebuild unit#16408
epage merged 4 commits intorust-lang:masterfrom
weihanglo:rebuild

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weihanglo commented Dec 17, 2025 •

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