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Allow phased initializing structs#152774

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dingxiangfei2009:partial-init
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Allow phased initializing structs#152774
dingxiangfei2009 wants to merge 1 commit intorust-lang:mainfrom
dingxiangfei2009:partial-init

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@dingxiangfei2009 dingxiangfei2009 commented Feb 17, 2026

This PR introduces an unstable feature partial_init_nodrop_types. This work corresponds to the new action item in rust-lang/rust-project-goals#548.

Action Items

  • What should we do with non_exhaustive?

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Allow partially initializing structs
b53c9d8 
Signed-off-by: Xiangfei Ding <dingxiangfei2009@protonmail.ch>
@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Feb 17, 2026
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dingxiangfei2009 commented Feb 17, 2026 •
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cc @BennoLossin @nxsaken FYI.

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rust-log-analyzer commented Feb 17, 2026

The job aarch64-gnu-llvm-20-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot) 
##[group]Runner Image Provisioner
Hosted Compute Agent
Version: 20260123.484
Commit: 6bd6555ca37d84114959e1c76d2c01448ff61c5d
Build Date: 2026-01-23T19:41:17Z
Worker ID: {796d113c-91b6-401c-a511-3bf8d6f3122a}
Azure Region: southcentralus
##[endgroup]
##[group]VM Image
- OS: Linux (arm64)
- Source: Partner
- Name: Ubuntu 24.04 by Arm Limited
---
REPOSITORY                                   TAG       IMAGE ID       CREATED       SIZE
ghcr.io/dependabot/dependabot-updater-core   latest    afc745c7535d   3 weeks ago   783MB
=> Removing docker images...
Deleted Images:
untagged: ghcr.io/dependabot/dependabot-updater-core:latest
untagged: ghcr.io/dependabot/dependabot-updater-core@sha256:faae3d3a1dedd24cde388bb506bbacc0f7ed1eae99ebac129af66acd8540c84a
deleted: sha256:afc745c7535da1bb12f92c273b9a7e9c52c3f12c5873714b2542da259c6d9769
deleted: sha256:64e147d5e54d9be8b8aa322e511cda02296eda4b8b8d063c6a314833aca50e29
deleted: sha256:5cba409bb463f4e7fa1a19f695450170422582c1bc7c0e934d893b4e5f558bc6
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---
fmt: checked 6701 files
tidy check
tidy [rustdoc_json (src)]: `rustdoc-json-types` modified, checking format version
tidy: Skipping binary file check, read-only filesystem
tidy [features]: /checkout/compiler/rustc_feature/src/unstable.rs:615: no tracking issue for feature partial_init_nodrop_types
tidy [features]: FAIL
tidy: The following check failed: features
Bootstrap failed while executing `--stage 2 test --skip tests --skip coverage-map --skip coverage-run --skip library --skip tidyselftest`
Command `/checkout/obj/build/aarch64-unknown-linux-gnu/stage1-tools-bin/rust-tidy --root-path=/checkout --cargo-path=/checkout/obj/build/aarch64-unknown-linux-gnu/stage0/bin/cargo --output-dir=/checkout/obj/build --concurrency=4 --npm-path=yarn` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:1612:23
Executed at: src/bootstrap/src/core/build_steps/test.rs:1365:29

Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:00:51
  local time: Tue Feb 17 21:50:05 UTC 2026
  network time: Tue, 17 Feb 2026 21:50:05 GMT
##[error]Process completed with exit code 1.
##[group]Run echo "disk usage:"

BennoLossin
BennoLossin reviewed Feb 17, 2026
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@BennoLossin BennoLossin left a comment •
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Very cool to see that it's less than 200 lines changed!

Just two small things that I noticed. I can't speak on any of the actual modifications :)

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tests/ui/feature-gates/feature-gate-partial-init-nodrop-types.stderr
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This is missing a feature gate error.

compiler/rustc_feature/src/unstable.rs
/// Allows using `#[optimize(X)]`.
(unstable, optimize_attribute, "1.34.0", Some(54882)),
/// Allows partial initialisation of no-Drop `struct`s and tuples.
(unstable, partial_init_nodrop_types, "CURRENT_RUSTC_VERSION", None),
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Suggested change
(unstable, partial_init_nodrop_types, "CURRENT_RUSTC_VERSION", None),
(unstable, partial_init_locals, "CURRENT_RUSTC_VERSION", None),

I'd call out that this is specifically about local variables. I don't think we need the "nodrop_types" postfix. I'd expect that once we have the explicit_drop_arming feature we just allow combining the two features.

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BennoLossin commented Feb 17, 2026

Regarding non-exhaustive: I think it's pretty simple, the reference already covers all of this:

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