Some of rustdoc's output is not stable #119597
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This was referenced Jan 5, 2024
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Judging by #119609 (comment), these fluctuations can be unstable under architecture. |
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I had to |
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cc #120371 |
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…meta-changes, r=<try> [try-only] [demo] rustdoc is unstable under rmeta changes Part of rust-lang#119597.
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I can no longer reproduce #119609 (comment), see #121486 but still |
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…s, r=<try>
[perf-only] rustdoc: synthetic impls: auto traits: Fx{Hash↦Index}{Map,Set}
Part of rust-lang#119597 and rust-lang#113015.
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…mpl-synth, r=<try> rustdoc: heavily simplify the synthesis of auto trait impls `gd --numstat HEAD~2 HEAD src/librustdoc/clean/auto_trait.rs` **+315 -705** 🟩🟥🟥🟥⬛ --- As outlined in issue rust-lang#113015, there are currently 3[^1] large separate routines that “clean” `rustc_middle::ty` data types related to generics & predicates to rustdoc data types. Every single one has their own kinds of bugs. While I've patched a lot of bugs in each of the routines in the past, it's about time to unify them. This PR is only the first in a series. It completely *yanks* the custom “bounds cleaning” of mod `auto_trait` and reuses the routines found in mod `simplify`. As mentioned, `simplify` is also flawed but still it's more complete than `auto_trait`'s routines. See also my review comment over at `tests/rustdoc/synthetic_auto/bounds.rs`. This is preparatory work for rewriting “bounds cleaning” in follow-up PRs in order to finally [fix] rust-lang#113015. Apart from that, I've eliminated all potential sources of *unstable rendering output*. See also rust-lang#119597. I'm pretty sure this fixes rust-lang#119597. This PR does not attempt to fix [any other issues related to synthetic auto trait impls](https://github.com/rust-lang/rust/issues?q=is%3Aissue+is%3Aopen+label%3AA-synthetic-impls%20label%3AA-auto-traits). However, it's definitely meant to be a *stepping stone* by making `auto_trait` more contributor friendly. --- * Replace `FxHash{Map,Set}` with `FxIndex{Map,Set}` to guarantee a stable / more predictable iteration order * Or as a perf opt, `UnordSet` (a thin wrapper around `FxHashSet`) in cases where we never iterate over the set. * Remove the types `RegionTarget` and `RegionDeps` from `librustdoc`. They were duplicates of the identical types found in `rustc`. Just import them from `rustc`. For some reason, they were duplicated when splitting `auto_trait` in two in rust-lang#49711. * Get rid of the useless “type namespace” `AutoTraitFinder` in `librustdoc` * The struct only held a `DocContext`, it was over-engineered * Turn the associated functions into free ones * Eliminates rightward drift; increases legibility * `rustc` also contains a useless `AutoTraitFinder` struct but I plan on removing that in a follow-up PR * Rename a bunch of methods to be way more descriptive * Eliminate `use super::*;` * Lead to `clean/mod.rs` accumulating a lot of unnecessary imports and therefore * made `auto_traits` less modular I plan on adding extensive documentation to `librustdoc`'s `auto_trait` in follow-up PRs. I don't want to do that in this PR because further refactoring & bug fix PRs may alter the overall structure of `librustdoc`'s & `rustc`'s `auto_trait` modules to a great degree. I'm slowly digging into the dark details of `rustc`'s `auto_trait` module again and once I have the full picture I will be able to provide proper docs. --- While this PR does indeed touch `rustc`'s `auto_trait` — mostly tiny refactorings — I argue this PR doesn't need any compiler reviewers next to rustdoc ones since that module falls under the purview of rustdoc — it used to be part of `librustdoc` after all (rust-lang#49711). Sorry for not having split this into more commits. If you'd like me to I can try to retroactively separate it into more atomic commits. However, I don't know if that would actually make reviewing this PR easier. r? `@GuillaumeGomez` [^1]: Or even 4 depending on the way you're counting.
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Seemingly innocuous and irrelevant modifications to a crate (like the reordering, addition or removal of unrelated items) may alter rustdoc's output compared to a previous build (which often manifests itself in a change in the order of “the things we are interested in”1).
I presume that this can only affect things for which rustdoc needs to look at the crate metadata (e.g., cross-crate re-exports and synthetic impls (blanket and auto-trait impls)).
I'm not in the know regarding the root cause since I don't know much about the internals of the crate metadata format (layout, serialization, deserialization). I suspect it might have something to do with the use of
FxHash{Set,Map}s during or after deserialization but that could be flat out wrong.Maybe it isn't even related to
rmetabut only toFxHash{Set,Map}, I really don't know. I just know that these kinds of “fluctuations” are stable under recompilation (of the input crate(s) and of rustdoc itself) and under reruns (of rustdoc) and only unstable under what I have inferred to be “crate metadata changes”. So while rustdoc's output is apparently deterministic, it's not necessarily fully predictable.Concrete examples and elaborations can be found below:
Footnotes
Ideally, the order wouldn't change at all and take the order either from the source code or from some predictable or known ordering (alphabetical, etc.) ↩
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