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bors 0e21dbf212 Auto merge of #129317 - compiler-errors:expectation-subtyping, r=lcnr 
Use equality when relating formal and expected type in arg checking

#129059 uncovered an interesting issue in argument checking. When we check arguments, we create three sets of types:
* Formals
* Expected
* Actuals

The **actuals** are the types of the argument expressions themselves. The **formals** are the types from the signature that we're checking. The **expected** types are the formal types, but passed through `expected_inputs_for_expected_outputs`:

a971212545/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs (L691-L725)

This method attempts to constrain the formal inputs by relating the [expectation](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir_typeck/expectation/enum.Expectation.html) of the call expression and the formal output.

When we check an argument, we get the expression's actual type, and then we first attempt to coerce it to the expected type:

a971212545/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs (L280-L293)

Then we subtype the expected type and the formal type:

a971212545/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs (L299-L305)

However, since we are now recording the right coercion target (since #129059), we now end up recording the expected type to the typeck results, rather than the actual.

Since that expected type was [fudged](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_infer/infer/struct.InferCtxt.html#method.fudge_inference_if_ok), it has fresh variables. And since the expected type is only subtyped against the formal type, if that expected type has a bivariant parameter, it will likely remain unconstrained since `Covariant * Bivariant = Bivariant` according to [xform](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/enum.Variance.html#method.xform). This leads to an unconstrained type variable in writeback.

AFAICT, there's no reason for us to be using subtyping here, though. The expected output is already related to the expectation by subtyping:

a971212545/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs (L713)

So the formals don't need "another" indirection of subtyping in the argument checking... So I've changed it to use equality here. We could alternatively fix this by requiring WF for all the expected types to constrain their bivariant parameters, but this seems a bit overkill.

Fixes #129286
2024-09-02 16:08:50 +00:00
.cargo fix: Fix generated markers not being patchable in package.json 2024-06-08 12:54:43 +02:00
.github Only keep lib/ in publish-libs 2024-08-12 13:45:38 +03:00
.vscode feat: use vscode log format for client logs 2024-07-27 21:43:35 -07:00
assets Automatically change text color in logo based on dark mode 2022-03-06 23:06:53 +11:00
bench_data Spelling 2023-04-19 09:45:55 -04:00
crates Rollup merge of #129207 - GrigorenkoPV:elided-is-named, r=cjgillot 2024-09-01 03:58:03 +02:00
docs Auto merge of #17857 - ChayimFriedman2:rust-project-cfg-group, r=Veykril 2024-08-23 10:01:35 +00:00
editors/code Old configs are back 2024-08-20 12:35:56 +02:00
lib Use crossbeam-channel from the workspace 2024-08-09 23:48:03 +02:00
xtask internal: Properly check the edition for edition dependent syntax kinds 2024-08-15 15:57:47 +02:00
.editorconfig add max_line_length to .editorconfig 2024-01-20 17:14:00 +03:00
.git-blame-ignore-revs internal: Don't allocate autoderef steps when not needed 2024-08-25 13:12:07 +02:00
.gitattributes Fix .gitattributes for test_data 2022-07-24 14:05:35 +02:00
.gitignore internal: add "Shuffle Crate Graph" command 2021-12-07 16:37:19 +01:00
.typos.toml Implement rough symbol interning infra 2024-07-12 16:01:47 +02:00
Cargo.lock Auto merge of #17907 - ChayimFriedman2:no-once_cell, r=Veykril 2024-08-16 07:05:59 +00:00
Cargo.toml Improve proc-macro panic message and workspace loading failure diagnostic 2024-08-22 18:46:23 +02:00
clippy.toml Lint debug prints and disallowed types with clippy 2024-02-01 17:57:27 +01:00
CONTRIBUTING.md Add CONTRIBUTING.md 2024-04-18 10:24:40 +02:00
LICENSE-APACHE Drop Apache license appendices 2024-08-27 14:52:34 +03:00
LICENSE-MIT Licenses 2018-01-10 22:47:04 +03:00
PRIVACY.md Update privacy note 2021-12-23 14:04:15 +02:00
README.md Add CONTRIBUTING.md 2024-04-18 10:24:40 +02:00
rust-bors.toml Prepare for rust-bors 2023-10-05 15:26:09 +03:00
rust-version Preparing for merge from rust-lang/rust 2024-08-29 10:02:05 +03:00
rustfmt.toml Shuffle hir-expand things around 2024-01-26 19:28:39 +01:00
triagebot.toml Update triagebot.toml 2024-06-27 10:32:13 +02:00

README.md

rust-analyzer logo

rust-analyzer is a modular compiler frontend for the Rust language. It is a part of a larger rls-2.0 effort to create excellent IDE support for Rust.

Quick Start

https://rust-analyzer.github.io/manual.html#installation

Documentation

If you want to contribute to rust-analyzer check out the CONTRIBUTING.md or if you are just curious about how things work under the hood, check the ./docs/dev folder.

If you want to use rust-analyzer's language server with your editor of choice, check the manual folder. It also contains some tips & tricks to help you be more productive when using rust-analyzer.

Security and Privacy

See the corresponding sections of the manual.

Communication

For usage and troubleshooting requests, please use "IDEs and Editors" category of the Rust forum:

https://users.rust-lang.org/c/ide/14

For questions about development and implementation, join rust-analyzer working group on Zulip:

https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Frust-analyzer

Quick Links

License

rust-analyzer is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-APACHE and LICENSE-MIT for details.