`librustdoc`: more `impl fmt::Display` #138455

yotamofek · 2025-03-13T13:51:36Z

Continuation of #137425 and #136828 and #136784
Working towards getting rid of the write_str helper
r? @GuillaumeGomez (if you want!)

rustbot · 2025-03-13T13:51:43Z

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

yotamofek · 2025-03-13T13:53:09Z

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged. Otherwise, you can ignore this comment.

This is intentional, I'm pulling in latest version of either with impl fmt::Write for Either (cc & thanks @jswrenn and @cuviper)

yotamofek · 2025-03-13T13:53:50Z

Perf is neutral locally, but I'll request a run on CI just to be sure.

GuillaumeGomez · 2025-03-13T13:55:14Z

src/librustdoc/html/markdown.rs

-            &added_classes,
+        let s = format!(
+            "\n{}",
+            highlight::render_example_with_highlighting(


Not sure this change is good considering we need to allocate a string in any case but relying on format!.

I think this will end up behaving exactly the same. It will construct the string piece-by-piece.
It would only matter if we used String::with_capacity, otherwise .pushing into a string directly, or using format!(), are the same in terms of reallocations and such.
(maybe I'm missing something?)

GuillaumeGomez · 2025-03-13T14:02:18Z

src/librustdoc/html/highlight.rs

@@ -6,16 +6,17 @@
 //! Use the `render_with_highlighting` to highlight some rust code.


Same in this file: I don't expect any improvement in performance considering it's always pushing into a string and it makes the code more complex.

The point of this PR in itself isn't performance.

My end-goal is to try to make ALL the rendering lazy, and then we could ideally write into a BufWriter that wraps the actual file, instead of writing everything to a String first, and then to the file system.
I do believe that that would be good for performance, because it should minimize the number of reallocs needed for rendering a single file. And maybe we could reuse the underlying buffer from BufWriter, which would be even better.
But such a change would be huge and I don't want to do it in one PR, so in the meanwhile I'm trying to put out small PRs that make progress towards that goal without hurting performance - so this PR being neutral in a perf run would be a success, as far as I'm concerned.

I also want to get rid of that write_str helper I introduced in #136784, since it's very verbose (because it needs format_args!()) and I intended it as a stopgap measure.

The only change to the code in this file (if you view the diff w/o whitespace) is the fmt::from_fn() and extra indentation it causes, which isn't great, but I think that the removal of all the format_args!() makes up for it. That's just my personal opinion, of course :)

Anyways, if you don't like the direction I'm going in let me know, and, obviously, feel free to close this PR if you think it's not improving the code at all! I'm thankful for the time you put into reviewing all my PRs 🙏

I'm fine with the rest of the changes. In highlight.rs though a bit less.

I undid the unrelated changes in highlight.rs, let me know if it's better now.

Sorry but still the same, for now I only see it as a code complexity increase for no gain. ^^'

Sorry for the delay, was traveling 😁
Undid the changes in this file, will figure it out in the future.

bors · 2025-04-08T16:59:32Z

☔ The latest upstream changes (presumably #139525) made this pull request unmergeable. Please resolve the merge conflicts.

…ite`

GuillaumeGomez · 2025-04-15T10:23:22Z

Looks all good now, thanks!

Let's just run a perf check before r+.

@bors try @rust-timer queue

bors · 2025-04-15T10:24:33Z

⌛ Trying commit 8dd1cbb with merge 6f904d8...

…ay, r=<try> `librustdoc`: more `impl fmt::Display` Continuation of rust-lang#137425 and rust-lang#136828 and rust-lang#136784 Working towards getting rid of the `write_str` helper r? `@GuillaumeGomez` (if you want!)

bors · 2025-04-15T12:28:58Z

☀️ Try build successful - checks-actions
Build commit: 6f904d8 (6f904d8d1b7524acaf443f021e25d28b0e89b3be)

rust-timer · 2025-04-15T13:47:16Z

Finished benchmarking commit (6f904d8): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

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

Instruction count

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

Max RSS (memory usage)

Results (primary 0.5%, secondary -2.5%)

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)	0.8%	[0.5%, 1.9%]	5
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	2
Improvements ✅ (secondary)	-2.5%	[-2.5%, -2.5%]	1
All ❌✅ (primary)	0.5%	[-0.4%, 1.9%]	7

Cycles

Results (primary 0.5%, secondary -2.5%)

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)	0.5%	[0.4%, 0.7%]	5
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.5%	[-2.5%, -2.5%]	1
All ❌✅ (primary)	0.5%	[0.4%, 0.7%]	5

Binary size

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

Bootstrap: 781.063s -> 781.152s (0.01%)
Artifact size: 365.12 MiB -> 365.12 MiB (-0.00%)

GuillaumeGomez · 2025-04-15T13:48:24Z

Confirmed that there are no perf changes, so rollup it is. Thanks!

@bors r+ rollup

bors · 2025-04-15T13:48:27Z

📌 Commit 8dd1cbb has been approved by GuillaumeGomez

It is now in the queue for this repository.

…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#138455 (`librustdoc`: more `impl fmt::Display`) - rust-lang#139818 (Normalize ADT field in `find_tails_for_unsizing`) - rust-lang#139819 (Use `rust-cache` to speed-up `citool` compilation) - rust-lang#139824 (Remove safe remove) - rust-lang#139848 ( Reduce kw::Empty usage, part 5) - rust-lang#139859 (CI: rename MacOS runner) - rust-lang#139877 (Add warning comment to `Take::get_ref` and `Chain::get_ref`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#138455 - yotamofek:pr/rustdoc/more-impl-display, r=GuillaumeGomez `librustdoc`: more `impl fmt::Display` Continuation of rust-lang#137425 and rust-lang#136828 and rust-lang#136784 Working towards getting rid of the `write_str` helper r? `@GuillaumeGomez` (if you want!)

rustbot assigned GuillaumeGomez Mar 13, 2025

GuillaumeGomez reviewed Mar 13, 2025

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yotamofek force-pushed the pr/rustdoc/more-impl-display branch from f8f7bc2 to f22e94c Compare March 14, 2025 14:54

yotamofek force-pushed the pr/rustdoc/more-impl-display branch from f22e94c to cf9cf6b Compare March 25, 2025 20:08

yotamofek force-pushed the pr/rustdoc/more-impl-display branch from cf9cf6b to b51e696 Compare April 8, 2025 17:28

yotamofek added 4 commits April 10, 2025 16:02

make AllTypes::print return impl fmt::Display

250a1aa

make link_tooltip return impl fmt::Display

642995c

make doc_impl_item and render_default_items receive `impl fmt::Wr…

f7640d5

…ite`

lazify render_assoc_items_inner

8dd1cbb

yotamofek force-pushed the pr/rustdoc/more-impl-display branch from b51e696 to 8dd1cbb Compare April 10, 2025 16:03

yotamofek requested a review from GuillaumeGomez April 15, 2025 09:41

GuillaumeGomez approved these changes Apr 15, 2025

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Apr 15, 2025

bors 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 Apr 15, 2025

matthiaskrgr mentioned this pull request Apr 15, 2025

Rollup of 7 pull requests #139881

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bors merged commit ca0b7f4 into rust-lang:master Apr 15, 2025
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rustbot added this to the 1.88.0 milestone Apr 15, 2025

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`librustdoc`: more `impl fmt::Display` #138455

`librustdoc`: more `impl fmt::Display` #138455

yotamofek commented Mar 13, 2025

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bors commented Apr 15, 2025

		@@ -6,16 +6,17 @@
		//! Use the `render_with_highlighting` to highlight some rust code.

librustdoc: more impl fmt::Display #138455

librustdoc: more impl fmt::Display #138455

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rust-timer commented Apr 15, 2025

Overall result: no relevant changes - no action needed

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`librustdoc`: more `impl fmt::Display` #138455

`librustdoc`: more `impl fmt::Display` #138455

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