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Diagnostic says method is available for a type it is not, when using const generics #124946

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j-browne opened this issue May 9, 2024 · 0 comments · Fixed by #125080
Closed

Diagnostic says method is available for a type it is not, when using const generics #124946

j-browne opened this issue May 9, 2024 · 0 comments · Fixed by #125080
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A-diagnostics Area: Messages for errors, warnings, and lints D-incorrect Diagnostics: A diagnostic that is giving misleading or incorrect information. D-papercut Diagnostics: An error or lint that needs small tweaks. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@j-browne
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j-browne commented May 9, 2024 •
edited by fmease

Code

https://play.rust-lang.org/?version=stable&mode=release&edition=2021&gist=eefb7934c44344c05b333afcbe6c4739

Current output

Compiling playground v0.0.1 (/playground)
error[E0599]: no method named `build` found for struct `Builder<false, true>` in the current scope
  --> src/main.rs:44:42
   |
9  | struct Builder<const AINIT: bool, const BINIT: bool> {
   | ---------------------------------------------------- method `build` not found for this struct
...
44 |     let item = Builder::new().with_b(()).build();
   |                --------------            ^^^^^ method not found in `Builder<false, true>`
   |                |
   |                method `build` is available on `Builder<false, false>`
   |
   = note: the method was found for
           - `Builder<true, true>`

For more information about this error, try `rustc --explain E0599`.

Desired output

Compiling playground v0.0.1 (/playground)
error[E0599]: no method named `build` found for struct `Builder<false, true>` in the current scope
  --> src/main.rs:44:42
   |
9  | struct Builder<const AINIT: bool, const BINIT: bool> {
   | ---------------------------------------------------- method `build` not found for this struct
...
44 |     let item = Builder::new().with_b(()).build();
   |                --------------            ^^^^^ method not found in `Builder<false, true>`
   |                |
   |                method `build` is available on `Builder<true, true>`
   |
   = note: the method was found for
           - `Builder<true, true>`

For more information about this error, try `rustc --explain E0599`.

or

Compiling playground v0.0.1 (/playground)
error[E0599]: no method named `build` found for struct `Builder<false, true>` in the current scope
  --> src/main.rs:44:42
   |
9  | struct Builder<const AINIT: bool, const BINIT: bool> {
   | ---------------------------------------------------- method `build` not found for this struct
...
44 |     let item = Builder::new().with_b(()).build();
   |                                          ^^^^^ method not found in `Builder<false, true>`
   |
   = note: the method was found for
           - `Builder<true, true>`

For more information about this error, try `rustc --explain E0599`.

Rationale and extra context

The diagnostic says "method build is available on Builder<false, false>", which is not true; it is available on Builder<true, true>, though.

The note does say that it is found for Builder<true, true>, though. This makes me wonder whether the former is even necessary or if it means something else that I do not understand (e.g., is there a difference between "is available on" and "was found for"?).

Other cases

If we call `Builder::new().build();`, we get a correct diagnostic:


   Compiling playground v0.0.1 (/playground)
error[E0599]: no method named `build` found for struct `Builder<false, false>` in the current scope
  --> src/main.rs:44:31
   |
9  | struct Builder<const AINIT: bool, const BINIT: bool> {
   | ---------------------------------------------------- method `build` not found for this struct
...
44 |     let item = Builder::new().build();
   |                               ^^^^^ method not found in `Builder<false, false>`
   |
   = note: the method was found for
           - `Builder<true, true>`

For more information about this error, try `rustc --explain E0599`.

Rust Version

cargo 1.78.0 (54d8815d0 2024-03-26)
release: 1.78.0
commit-hash: 54d8815d04fa3816edc207bbc4dd36bf18014dbc
commit-date: 2024-03-26
host: x86_64-unknown-linux-gnu
libgit2: 1.7.2 (sys:0.18.2 vendored)
libcurl: 8.6.0-DEV (sys:0.4.72+curl-8.6.0 vendored ssl:OpenSSL/1.1.1w)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Arch Linux [64-bit]

Anything else?

No response
@j-browne j-browne added A-diagnostics Area: Messages for errors, warnings, and lints T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels May 9, 2024
@fmease fmease added D-papercut Diagnostics: An error or lint that needs small tweaks. D-incorrect Diagnostics: A diagnostic that is giving misleading or incorrect information. labels May 10, 2024
@bvanjoi bvanjoi mentioned this issue May 13, 2024
Merged
@bors bors closed this as completed in 8c64acd May 14, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this issue May 14, 2024
@rust-timer
Unrolled build for rust-lang#125080
3907877 
Rollup merge of rust-lang#125080 - bvanjoi:fix-124946, r=nnethercote

only find segs chain for missing methods when no available candidates

Fixes rust-lang#124946

This PR includes two changes:
- Extracting the lookup for the missing method in chains into a single function.
- Calling this function only when there are no candidates available.
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A-diagnostics Area: Messages for errors, warnings, and lints D-incorrect Diagnostics: A diagnostic that is giving misleading or incorrect information. D-papercut Diagnostics: An error or lint that needs small tweaks. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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only find segs chain for missing methods when no available candidates bvanjoi/rust
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@j-browne @fmease