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Improve path segment joining #143922

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nnethercote
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@nnethercote nnethercote commented Jul 14, 2025 •
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Currently paths are joined with :: in many places, in a variety of ways. This PR unifies things.

r? @petrochenkov

@nnethercote
Improve path segment joining.
34e72d1 
There are many places that join path segments with `::` to produce a
string. A lot of these use `join("::")`. Many in rustdoc use
`join_with_double_colon`, and a few use `.joined("..")`. One in Clippy
uses `itertools::join`. A couple of them look for `kw::PathRoot` in the
first segment, which can be important.

This commit introduces `rustc_ast::join_path_{syms,ident}` to do the
joining for everyone. `rustc_ast` is as good a location for these as
any, being the earliest-running of the several crates with a `Path`
type. Two functions are needed because `Ident` printing is more complex
than simple `Symbol` printing.

The commit also removes `join_with_double_colon`, and
`estimate_item_path_byte_length` with it.

There are still a handful of places that join strings with "::" that are
unchanged. They are not that important: some of them are in tests, and
some of them first split a path around "::" and then rejoin with "::".

This fixes one test case where `{{root}}` shows up in an error message.
@nnethercote
Use join_path_syms in one more place.
f0a57ad 
This one is a bit marginal, because the segments are a mix of symbols
and strings.
@rustbot rustbot added A-attributes Area: Attributes (`#[…]`, `#![…]`) S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-clippy Relevant to the Clippy team. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. T-rustdoc-frontend Relevant to the rustdoc-frontend team, which will review and decide on the web UI/UX output. labels Jul 14, 2025
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@bors try @rust-timer queue

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@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 14, 2025
bors added a commit that referenced this pull request Jul 14, 2025
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Auto merge of #143922 - nnethercote:join_path, r=<try>
c0eee71 
Improve path segment joining

r? `@ghost`
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bors commented Jul 14, 2025

⌛ Trying commit f0a57ad with merge c0eee71...

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bors commented Jul 14, 2025

☀️ Try build successful - checks-actions
Build commit: c0eee71 (c0eee7172cfb3e789622d2a94af20e4345fcc338)

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Finished benchmarking commit (c0eee71): comparison URL.

Overall result: ❌ regressions - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

mean range count
Regressions ❌
(primary)		 - - 0
Regressions ❌
(secondary)		 0.1% [0.1%, 0.1%] 1
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) - - 0

Max RSS (memory usage)

Results (primary -1.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

mean range count
Regressions ❌
(primary)		 8.9% [8.9%, 8.9%] 1
Regressions ❌
(secondary)		 - - 0
Improvements ✅
(primary)		 -6.8% [-7.0%, -6.6%] 2
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) -1.6% [-7.0%, 8.9%] 3

Cycles

Results (secondary -2.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

mean range count
Regressions ❌
(primary)		 - - 0
Regressions ❌
(secondary)		 - - 0
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 -2.5% [-2.5%, -2.5%] 1
All ❌✅ (primary) - - 0

Binary size

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

Bootstrap: 465.735s -> 464.956s (-0.17%)
Artifact size: 374.64 MiB -> 374.59 MiB (-0.01%)

@rustbot rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 14, 2025
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@jdonszelmann: you were talking about this a while back.

@camelid: this touches rustdoc in a lot of places, you might be interested.

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Performance is neutral, which is what I was aiming for, given that this code is hot in some cases, especially doc builds.

@bors rollup=maybe

@nnethercote nnethercote marked this pull request as ready for review July 14, 2025 22:46
@rustbot 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 Jul 14, 2025
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rustbot commented Jul 14, 2025

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

samueltardieu
samueltardieu approved these changes Jul 14, 2025
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On the Clippy side, nice improvements by using interned symbols in more places, this is what we've been aiming at.

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Lovely

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@samueltardieu samueltardieu samueltardieu approved these changes

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A-attributes Area: Attributes (`#[…]`, `#![…]`) S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-clippy Relevant to the Clippy team. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. T-rustdoc-frontend Relevant to the rustdoc-frontend team, which will review and decide on the web UI/UX output.
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