redesign stage 0 std #119899

onur-ozkan · 2024-01-12T17:57:42Z

Summary

Blog post: https://blog.rust-lang.org/inside-rust/2025/05/29/redesigning-the-initial-bootstrap-sequence/

This PR changes how bootstrap builds the stage 1 compiler by switching to precompiled stage 0 standard library instead of building the in-tree one. The goal was to update bootstrap to use the beta standard library at stage 0 rather than compiling it from source (see the motivation at rust-lang/compiler-team#619).

Previously, to build a stage 1 compiler bootstrap followed this path:

download stage0 compiler -> build in-tree std -> compile stage1 compiler with in-tree std

With this PR, the new path is:

download stage0 compiler -> compile stage1 compiler with precompiled stage0 std

This also means that cfg(bootstrap)/cfg(not(bootstrap)) is no longer needed for library development.

Building "library"

Since stage0 std is no longer in-tree x build/test/check library --stage 0 is now no-op. The minimum supported stage to build std is now 1. For the same reason, default stage values in the library profile is no longer 0.

Because building the in-tree library now requires a stage1 compiler, I highly recommend library developers to enable download-rustc to speed up compilation time.

Blog post: https://blog.rust-lang.org/inside-rust/2025/05/29/redesigning-the-initial-bootstrap-sequence/

If you encounter a bug or unexpected results please open a topic in the #t-infra/bootstrap Zulip channel or create a bootstrap issue.

(Review thread: https://rust-lang.zulipchat.com/#narrow/channel/326414-t-infra.2Fbootstrap/topic/Review.20thread.3A.20stage.200.20redesign.20PR/with/508271433)

~~Blocked on #122709 and #137215~~

try-job: dist-x86_64-linux
try-job: x86_64-msvc*
try-job: x86_64-apple-*
try-job: aarch64-apple
try-job: x86_64-gnu
try-job: x86_64-gnu-llvm*

rustbot · 2024-01-14T13:57:46Z

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

onur-ozkan · 2024-01-14T13:58:14Z

@rustbot ready

r? bootstrap
cc @rust-lang/libs

onur-ozkan · 2024-01-14T16:22:20Z

@rustbot author (currently stage 2 std is copied from stage 1 and this behaviour should change with the beta std change)

bors · 2025-06-02T07:49:21Z

⌛ Testing commit a577bcc with merge 52882f6...

bors · 2025-06-02T11:05:57Z

☀️ Test successful - checks-actions
Approved by: albertlarsan68,jieyouxu,mark-simulacrum,kobzol,jyn514,Noratrieb,WaffleLapkin,RalfJung,bjorn3
Pushing 52882f6 to master...

github-actions · 2025-06-02T11:08:37Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 91fad92 (parent) -> 52882f6 (this PR)

Test differences

Show 3 test diffs

Stage 0

core::builder::tests::ci_rustc_if_unchanged_invalidate_on_library_changes_in_ci: pass -> [missing] (J0)

Additionally, 2 doctest diffs were found. These are ignored, as they are noisy.

Job group index

J0: aarch64-apple, aarch64-gnu, i686-gnu-2, i686-gnu-nopt-2, i686-msvc-2, x86_64-apple-1, x86_64-gnu, x86_64-gnu-llvm-19-1, x86_64-gnu-llvm-19-3, x86_64-gnu-llvm-20-1, x86_64-gnu-llvm-20-3, x86_64-gnu-nopt, x86_64-gnu-stable, x86_64-mingw-2, x86_64-msvc-2

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 52882f6522ae9f34f1d574b2efabc4b18e691ae0 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

x86_64-apple-2: 7074.7s -> 4265.1s (-39.7%)
dist-x86_64-apple: 11819.4s -> 9527.8s (-19.4%)
aarch64-gnu-debug: 4413.6s -> 3872.1s (-12.3%)
x86_64-gnu-llvm-19-1: 3945.8s -> 3707.9s (-6.0%)
aarch64-apple: 5149.6s -> 5447.6s (5.8%)
x86_64-gnu-llvm-19-3: 7233.4s -> 6817.9s (-5.7%)
x86_64-gnu-llvm-20-3: 7297.2s -> 6895.9s (-5.5%)
dist-apple-various: 6596.2s -> 6918.6s (4.9%)
i686-gnu-nopt-2: 6796.9s -> 6487.0s (-4.6%)
dist-x86_64-msvc-alt: 7741.1s -> 7396.8s (-4.4%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-06-02T12:46:40Z

Finished benchmarking commit (52882f6): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (secondary -0.8%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.6%	[0.6%, 2.8%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.4%	[-9.0%, -0.4%]	12
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary -0.4%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.7%	[0.5%, 0.8%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.9%	[-1.3%, -0.6%]	8
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 774.333s -> 743.462s (-3.99%)
Artifact size: 372.28 MiB -> 372.27 MiB (-0.01%)

…kingjubilee Remove bootstrap cfgs from library/ These `cfg(bootstrap)` are always false now that rust-lang#119899 has landed, and likewise `cfg(not(bootstrap))` is always true. Therefore, we don't need to wait for the usual stage0 bump to clean these up.

redesign stage 0 std follow-ups Various follow-ups pointed out on Zulip during post-merge discussions of [redesign stage 0 std rust-lang#119899](rust-lang#119899). r? `@jieyouxu` Fixes rust-lang#141902. Fixes rust-lang#141905. cc `@jyn514`

Rollup merge of #141914 - onur-ozkan:follow-ups, r=Kobzol redesign stage 0 std follow-ups Various follow-ups pointed out on Zulip during post-merge discussions of [redesign stage 0 std #119899](#119899). r? `@jieyouxu` Fixes #141902. Fixes #141905. cc `@jyn514`

…kingjubilee Remove bootstrap cfgs from library/ These `cfg(bootstrap)` are always false now that rust-lang#119899 has landed, and likewise `cfg(not(bootstrap))` is always true. Therefore, we don't need to wait for the usual stage0 bump to clean these up.

Rollup merge of #141925 - cuviper:vestigial-bootstrap, r=workingjubilee Remove bootstrap cfgs from library/ These `cfg(bootstrap)` are always false now that #119899 has landed, and likewise `cfg(not(bootstrap))` is always true. Therefore, we don't need to wait for the usual stage0 bump to clean these up.

Remove bootstrap cfgs from library/ These `cfg(bootstrap)` are always false now that rust-lang/rust#119899 has landed, and likewise `cfg(not(bootstrap))` is always true. Therefore, we don't need to wait for the usual stage0 bump to clean these up.

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 Jan 12, 2024

onur-ozkan 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-review Status: Awaiting review from the assignee but also interested parties. labels Jan 12, 2024

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rustbot added A-testsuite Area: The testsuite used to check the correctness of rustc T-infra Relevant to the infrastructure team, which will review and decide on the PR/issue. labels Jan 13, 2024

onur-ozkan force-pushed the redesign-stage0-std branch from 9fcee5c to 066ce06 Compare January 13, 2024 11:04

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onur-ozkan force-pushed the redesign-stage0-std branch from 066ce06 to 472c50c Compare January 13, 2024 13:09

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onur-ozkan force-pushed the redesign-stage0-std branch 2 times, most recently from ce81474 to b688ffa Compare January 13, 2024 15:51

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onur-ozkan force-pushed the redesign-stage0-std branch 6 times, most recently from 5f1747d to 00e59f0 Compare January 14, 2024 13:30

onur-ozkan marked this pull request as ready for review January 14, 2024 13:57

onur-ozkan changed the title ~~[WIP] redesign stage 0 std~~ redesign stage 0 std Jan 14, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jan 14, 2024

rustbot assigned albertlarsan68 Jan 14, 2024

onur-ozkan force-pushed the redesign-stage0-std branch from 00e59f0 to 8ac271c Compare January 14, 2024 14:41

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jan 14, 2024

bors added the merged-by-bors This PR was explicitly merged by bors. label Jun 2, 2025

bors merged commit 52882f6 into rust-lang:master Jun 2, 2025
11 checks passed

rustbot added this to the 1.89.0 milestone Jun 2, 2025

onur-ozkan deleted the redesign-stage0-std branch June 2, 2025 11:06

Mark-Simulacrum mentioned this pull request Jun 2, 2025

cfg(bootstrap) needed in test-float-parse #141900

Closed

jieyouxu mentioned this pull request Jun 2, 2025

Tracking issue for post stage 0 bootstrap sequence redesign follow-ups and bugs #141901

Open

jyn514 mentioned this pull request Jun 2, 2025

after stage0 redesign, x check defaults to building the compiler #141902

Closed

onur-ozkan mentioned this pull request Jun 2, 2025

redesign stage 0 std follow-ups #141914

Merged

oli-obk mentioned this pull request Jun 2, 2025

make RefCell unstably const #137843

Open

cuviper mentioned this pull request Jun 2, 2025

Remove bootstrap cfgs from library/ #141925

Merged

zachs18 mentioned this pull request Jun 3, 2025

./x.py test library fails when using the library profile (after stage0 redesign) #141983

Closed

lambdageek mentioned this pull request Jun 3, 2025

bootstrap: using a toolchain that includes 'rust-src', ./x check leaves a dirty working tree, fails to build #141991

Closed

m-ou-se mentioned this pull request Jun 4, 2025

Add Location::file_with_nul #135054

Open

jyn514 mentioned this pull request Jun 5, 2025

bootstrap blog post should document how x check has changed and what to do instead #142051

Open

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redesign stage 0 std #119899

redesign stage 0 std #119899

onur-ozkan commented Jan 12, 2024 •

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Stage 0

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redesign stage 0 std #119899

redesign stage 0 std #119899

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Summary

Building "library"

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Test differences

Stage 0

Job duration changes

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rust-timer commented Jun 2, 2025

Overall result: no relevant changes - no action needed

Instruction count

Max RSS (memory usage)

Cycles

Binary size

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onur-ozkan commented Jan 12, 2024 •

edited

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