Improve the diagnostics for unused generic params in ty aliases & permit bivariant but constrained params in LTAs #120556

fmease · 2024-02-01T15:06:25Z

Don't emit two errors (namely E0091 and E0392) for unused type parameters on lazy type aliases
Fix the diagnostic help message of E0392 for lazy type aliases: Don't talk about the “fields” of lazy type aliases (use the term “body” instead) and don't suggest PhantomData for them, it doesn't make much sense
Consolidate the diagnostics for E0091 (unused type parameters in type aliases) and E0392 (unused generic parameters due to bivariance) and make it translatable
- Still keep the error codes distinct (for now)
- Naturally leads to better diagnostics for E0091

Edit(2024-07-26): This PR starts allowing bivariant but constrained params in lazy type aliases just like in ADTs. E.g., type A<T, F> = F where F: Fn() -> T; (similar to struct S<T, F>(F) where F: Fn() -> T;); T is bivariant but constrained. E0091 for eager type aliases doesn't account for such a thing.

r? @oli-obk (to ballast your review load :P) or compiler

compiler/rustc_error_codes/src/error_codes/E0091.md

fmease · 2024-02-01T15:09:35Z

compiler/rustc_hir_analysis/src/check/wfcheck.rs

-        )
-    } else {
-        format!("consider removing `{param_name}` or referring to it in a field")
+    let param_name = param.name.ident();


I'm no longer extracting the Symbol from the Ident via param.name.ident().name since the Display impl for Ident accounts for escaping via r#. This way, we properly display r#if in type T<r#if> = (); as r#if instead of if.

fmease · 2024-02-01T15:11:38Z

tests/ui/const-generics/generic_arg_infer/infer-arg-test.stderr

@@ -10,14 +10,14 @@ error: expected identifier, found reserved identifier `_`
 LL | fn bad_infer_fn<_>() {}
   |                 ^ expected identifier, found reserved identifier

-error[E0392]: parameter `_` is never used
+error[E0392]: type parameter `_` is never used


I could add extra code for skipping this error entirely by delaying a bug on _ when checking the “usedness”. Not sure if it'd be worth it though.

It may be very hard to track the expected identifier, found reserved identifier error all the way into the type system. We'd probably have to add a GenericParamDefKind::Error to do that. May be worth exploring, but not in this PR

fmease · 2024-02-01T15:13:43Z

compiler/rustc_hir_analysis/src/check/check.rs

+            // FIXME: This assumes that elaborated `Sized` bounds come first (which does hold at the
+            // time of writing). This is a bit fragile since we later use the span to detect elaborated
+            // `Sized` bounds. If they came last for example, this would break `Trait + /*elab*/Sized`
+            // since it would overwrite the span of the user-written bound. This could be fixed by
+            // folding the spans with `Span::to` which requires a bit of effort I think.


Didn't want to deal with this right now but I can try to do so if you'd like me to. I think it'll be a bit nasty to implement though. Consider a hypothetical set of predicates like [<A as TraitA>, <B as TraitB>, /*elab*/<A as Sized>] (note: we need to merge the spans of the 0th and the 2nd predicate).

Maybe it's actually not that ugly to implement, I just haven't spent any time to think about this.

why does it rely on that? the spans differ, so both elaborated and user-written would end up in the hash set

🤦 it's a hashmap and this collect relies on the hash map impl overwriting with follow up items of the same key

seems fine to rely on this, there are tests after all

oli-obk · 2024-02-01T17:15:26Z

@bors r+ rollup

bors · 2024-02-01T17:15:28Z

📌 Commit 02320b5 has been approved by oli-obk

It is now in the queue for this repository.

bors · 2024-02-01T17:15:29Z

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

…m-diags, r=oli-obk Improve the diagnostics for unused generic parameters * Don't emit two errors (namely E0091 *and* E0392) for unused type parameters on *lazy* type aliases * Fix the diagnostic help message of E0392 for *lazy* type aliases: Don't talk about the “fields” of lazy type aliases (use the term “body” instead) and don't suggest `PhantomData` for them, it doesn't make much sense * Consolidate the diagnostics for E0091 (unused type parameters in type aliases) and E0392 (unused generic parameters due to bivariance) and make it translatable * Still keep the error codes distinct (for now) * Naturally leads to better diagnostics for E0091 r? `@oli-obk` (to ballast your review load :P) or compiler

…m-diags, r=oli-obk Improve the diagnostics for unused generic parameters * Don't emit two errors (namely E0091 *and* E0392) for unused type parameters on *lazy* type aliases * Fix the diagnostic help message of E0392 for *lazy* type aliases: Don't talk about the “fields” of lazy type aliases (use the term “body” instead) and don't suggest `PhantomData` for them, it doesn't make much sense * Consolidate the diagnostics for E0091 (unused type parameters in type aliases) and E0392 (unused generic parameters due to bivariance) and make it translatable * Still keep the error codes distinct (for now) * Naturally leads to better diagnostics for E0091 r? ``@oli-obk`` (to ballast your review load :P) or compiler

…iaskrgr Rollup of 9 pull requests Successful merges: - rust-lang#119759 (Add FileCheck annotations to dataflow-const-prop tests) - rust-lang#120323 (On E0277 be clearer about implicit `Sized` bounds on type params and assoc types) - rust-lang#120473 (Only suggest removal of `as_*` and `to_` conversion methods on E0308) - rust-lang#120520 (Some cleanups around diagnostic levels.) - rust-lang#120540 (add test for try-block-in-match-arm) - rust-lang#120547 (`#![feature(inline_const_pat)]` is no longer incomplete) - rust-lang#120552 (Correctly check `never_type` feature gating) - rust-lang#120555 (put pnkfelix (me) back on the review queue.) - rust-lang#120556 (Improve the diagnostics for unused generic parameters) r? `@ghost` `@rustbot` modify labels: rollup

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#119759 (Add FileCheck annotations to dataflow-const-prop tests) - rust-lang#120323 (On E0277 be clearer about implicit `Sized` bounds on type params and assoc types) - rust-lang#120473 (Only suggest removal of `as_*` and `to_` conversion methods on E0308) - rust-lang#120540 (add test for try-block-in-match-arm) - rust-lang#120547 (`#![feature(inline_const_pat)]` is no longer incomplete) - rust-lang#120552 (Correctly check `never_type` feature gating) - rust-lang#120555 (put pnkfelix (me) back on the review queue.) - rust-lang#120556 (Improve the diagnostics for unused generic parameters) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#120556 - fmease:improve-unused-generic-param-diags, r=oli-obk Improve the diagnostics for unused generic parameters * Don't emit two errors (namely E0091 *and* E0392) for unused type parameters on *lazy* type aliases * Fix the diagnostic help message of E0392 for *lazy* type aliases: Don't talk about the “fields” of lazy type aliases (use the term “body” instead) and don't suggest `PhantomData` for them, it doesn't make much sense * Consolidate the diagnostics for E0091 (unused type parameters in type aliases) and E0392 (unused generic parameters due to bivariance) and make it translatable * Still keep the error codes distinct (for now) * Naturally leads to better diagnostics for E0091 r? ```@oli-obk``` (to ballast your review load :P) or compiler

rustbot assigned oli-obk Feb 1, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Feb 1, 2024

fmease commented Feb 1, 2024

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compiler/rustc_error_codes/src/error_codes/E0091.md Show resolved Hide resolved

fmease commented Feb 1, 2024

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Improve the diagnostics for unused generic parameters

02320b5

fmease force-pushed the improve-unused-generic-param-diags branch from 7a4f93d to 02320b5 Compare February 1, 2024 15:18

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 1, 2024

matthiaskrgr mentioned this pull request Feb 1, 2024

Rollup of 9 pull requests #120560

Closed

matthiaskrgr mentioned this pull request Feb 1, 2024

Rollup of 9 pull requests #120561

Closed

matthiaskrgr mentioned this pull request Feb 4, 2024

Rollup of 8 pull requests #120649

Merged

bors merged commit 7fa99bf into rust-lang:master Feb 5, 2024
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rustbot added this to the 1.78.0 milestone Feb 5, 2024

fmease deleted the improve-unused-generic-param-diags branch February 5, 2024 01:11

fmease mentioned this pull request Feb 22, 2024

Tracking issue for lazy type aliases #112792

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fmease changed the title ~~Improve the diagnostics for unused generic parameters~~ Improve the diagnostics for unused generic parameters in type aliases & permit bivariant but constrained params in LTAs Jul 26, 2024

fmease added the F-lazy_type_alias `#![feature(lazy_type_alias)]` label Jul 26, 2024

fmease changed the title ~~Improve the diagnostics for unused generic parameters in type aliases & permit bivariant but constrained params in LTAs~~ Improve the diagnostics for unused generic params in ty aliases & permit bivariant but constrained params in LTAs Jul 26, 2024

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Improve the diagnostics for unused generic params in ty aliases & permit bivariant but constrained params in LTAs #120556

Improve the diagnostics for unused generic params in ty aliases & permit bivariant but constrained params in LTAs #120556

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Improve the diagnostics for unused generic params in ty aliases & permit bivariant but constrained params in LTAs #120556

Improve the diagnostics for unused generic params in ty aliases & permit bivariant but constrained params in LTAs #120556

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