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Rename MetaSized trait to SizeOfVal#154374

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lqd wants to merge 7 commits intorust-lang:mainfrom
lqd:rename-metasized
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Rename MetaSized trait to SizeOfVal#154374
lqd wants to merge 7 commits intorust-lang:mainfrom
lqd:rename-metasized

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@lqd lqd commented Mar 25, 2026

This renames the MetaSized trait from the Sized Hierarchy to SizeOfVal, as the consensus on t-lang from last week's meeting.

I've tried to split the full change into self-contained commits for easier review.

rust/clippy/rustdoc tests all seem to pass locally, but I haven't tried the full cartesian product of all our bootstrap settings and optional submodules, so I'm opening this as draft to first see what breaks on CI.

Of note:

  • r-a uses lang items and rustc crates, but from crates.io, so the r-a tests should not break from this PR per se, but would whenever the autopublished crates are used there. I will eventually open a PR there to handle the renaming as well.
  • cargo also uses lang items in its tests, so it'll be interesting to see whether they fail in this PR, or would once cargo updates to the next nightly containing this PR after it lands. Either way, I will also open a PR there to handle the renaming.
  • I don't know if we need some cfg bootstrap choreography to land this, I thought so things seem to build locally. The dev guide mentions how to run std tests on stage 0, but that command doesn't work anymore. We'll see what PR CI says about needing to do the renaming in multiple steps.

cc @davidtwco as well

@rustbot rustbot added A-run-make Area: port run-make Makefiles to rmake.rs A-rustc-dev-guide Area: rustc-dev-guide A-rustdoc-json Area: Rustdoc JSON backend A-test-infra-minicore Area: `minicore` test auxiliary and `//@ add-core-stubs` PG-exploit-mitigations Project group: Exploit mitigations 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-libs Relevant to the library 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. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels Mar 25, 2026
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lqd commented Mar 25, 2026

I guess it's fine for PR CI.

@bors try jobs=dist-x86_64-linux

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rust-bors bot pushed a commit that referenced this pull request Mar 25, 2026
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Auto merge of #154374 - lqd:rename-metasized, r=<try>
2ea60dd 
Rename `MetaSized` trait to `SizeOfVal`


try-job: dist-x86_64-linux
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rust-bors bot commented Mar 25, 2026

☀️ Try build successful (CI)
Build commit: 2ea60dd (2ea60dd27b62adb4b3b558d80261fe0174d408f7, parent: 64d5cb603b9caf9063d27d64fdfa61fa7af3b98f)

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lqd commented Mar 25, 2026

Cool, the opt-dist tests passed.

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lqd commented Mar 26, 2026 •
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A couple of well-known projects are "using" MetaSized:

  • charon
  • verus
  • ferrocene

The first two make light use of it, but I'll also open a couple PRs there. Ferrocene looks like it gets it from us upstream, so I assume this will be invisible. The other projects are mostly similar to forks, or copying parts of libcore so I assume it's as fine as we've done in the past like #130225.

Even if this is still unstable, and unlikely to see a lot of use, it could be interesting to check. The crater queue is currently busy, but it's OK. We could open issues in other projects early if we see anything in a run for informational purposes.

@bors try

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rust-bors bot pushed a commit that referenced this pull request Mar 26, 2026
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Auto merge of #154374 - lqd:rename-metasized, r=<try>
dffc6a7 
Rename `MetaSized` trait to `SizeOfVal`
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rust-bors bot commented Mar 26, 2026

☀️ Try build successful (CI)
Build commit: dffc6a7 (dffc6a7258307e464c860a62a02d61b32a0cfcf0, parent: 3ea2fbcb2a872b7e1fa3cada256f8e97f9e6636f)

davidtwco
davidtwco approved these changes Mar 26, 2026
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Implementation all looks good to me, r=me once you're confident it'll merge

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lqd added 7 commits March 27, 2026 10:17
@lqd
change meta_sized lang item external name to size_of_val
e8467cb 
t-lang consensus is to name the `MetaSized` trait as `SizeOfVal`: this updates
the lang-item external name as its own independent change for easier reviewing.
@lqd
change MetaSized lang item internal name to SizeOfVal
40220cc
@lqd
rename SizedTraitKind::MetaSized variant
b6c685b
@lqd
rename meta_sized_trait lang item getter
8d825c1
@lqd
rename references to MetaSized trait in compiler and rustdoc
becfc0a
@lqd
rename MetaSized trait in library and no_core/mini_core tests
877e1de 
That includes:
- the libcore trait, and `library` uses of the lang item
- top-level tests using the lang item in no_core or mini_core tests
- tests in codegen backends, clippy, and rustdoc
@lqd
finishing touches of the renaming
541d2d7 
The last bits of the renaming:

- rustfmted the one compiler expression that needed reflowing
- blessed test expectations
- updated and renamed the tests whose name referenced "metasized"
- updated the one mention in the rustc-dev-guide
@lqd lqd force-pushed the rename-metasized branch from 13cbf33 to 541d2d7 Compare March 27, 2026 10:04
@nia-e nia-e added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Apr 2, 2026
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nia-e commented Apr 2, 2026

Nominated for libs-api discussion regarding naming; see https://rust-lang.zulipchat.com/#narrow/channel/219381-t-libs/topic/vibeck.20on.20Sized.20Hierarchy.20trait.20names/

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rust-bors bot commented Apr 3, 2026

☔ The latest upstream changes (presumably #154727) made this pull request unmergeable. Please resolve the merge conflicts.

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A-run-make Area: port run-make Makefiles to rmake.rs A-rustc-dev-guide Area: rustc-dev-guide A-rustdoc-json Area: Rustdoc JSON backend A-test-infra-minicore Area: `minicore` test auxiliary and `//@ add-core-stubs` I-libs-api-nominated Nominated for discussion during a libs-api team meeting. PG-exploit-mitigations Project group: Exploit mitigations 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-libs Relevant to the library 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. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver)

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