Unconstrained parameter fix by TomtheCoder2 · Pull Request #148788 · rust-lang/rust

TomtheCoder2 · 2025-11-10T14:17:59Z

This PR is an attempt to solve the issue described in the issue #107295

rustbot · 2025-11-10T14:18:03Z

This PR modifies tests/ui/issues/. If this PR is adding new tests to tests/ui/issues/,
please refrain from doing so, and instead add it to more descriptive subdirectories.

rustbot · 2025-11-10T14:18:06Z

r? @davidtwco

rustbot has assigned @davidtwco.
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rust-bors · 2026-01-13T00:02:13Z

☔ The latest upstream changes (presumably #150844) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2026-03-10T13:51:57Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

TomtheCoder2 · 2026-03-11T07:22:35Z

@rustbot ready

davidtwco

I'd appreciate it if you could squash your commits too

View changes since this review

davidtwco · 2026-03-25T14:11:20Z

+            return self.span.shrink_to_hi();
+        }
+
+        let is_impl_generic = |par: &&GenericParam<'_>| match par.kind {


Suggested change

let is_impl_generic = |par: &&GenericParam<'_>| match par.kind {

let is_param_explicit = |par: &&GenericParam<'_>| match par.kind {

davidtwco · 2026-03-25T14:16:12Z

+    let parameter_type = if is_lifetime { "lifetime" } else { "type" };
+    if is_param_used {
+        let msg = format!(
+            "make use of the {} parameter `{}` in the `self` type",


Suggested change

"make use of the {} parameter `{}` in the `self` type",

"make use of the {} parameter `{}` in the `{}` type",

Can you get the name of the Self type from its DefId?

davidtwco · 2026-03-25T14:17:15Z

+            Applicability::MaybeIncorrect,
+        );
+        if suggestions.len() == 2 {
+            let msg = format!("or make use of it");


Suggested change

let msg = format!("or make use of it");

let msg = format!("or use it");

davidtwco · 2026-03-25T14:18:23Z

+        let msg2 = format!(
+            "and add it to the struct definition of {} as well since it's used in the body of the impl",
+            tcx.def_path_str(struct_def_id)
+        );


You should probably use a MultiSpan with the definition and the impl and emit a single suggestion for this instead of two distinct suggestions but that would need to be applied together

And change the message to "use this type parameter in the type definition"

davidtwco · 2026-03-25T14:21:07Z

+/// - `impl<'a> Struct { ... }` where `'a` is unused -> suggests removing `'a`.
+/// - `impl<T> Struct { // T used in here }` where `T` is used in the body but not in the self type -> suggests adding `T` to the self type and struct definition.
+/// - `impl<T> Struct { ... }` where the struct has a generic parameter with a default -> suggests adding `T` to the self type.
+pub(crate) fn suggest_to_remove_or_use_generic(


Can you add your own test file that tests all of these cases specifically, as well as where the type is defined in another crate, or where the type is generated from a macro.

rustbot · 2026-04-29T22:42:03Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

When an unconstrained type or lifetime parameter is detected in an `impl`, provide more specific help based on its usage: - If the parameter is entirely unused, suggest removing it. - If it is used in the `impl` body but not the `Self` type, suggest including it in the `Self` type and the struct definition. This also adds a comprehensive UI test for these cases.

TomtheCoder2 · 2026-04-30T10:33:16Z

I have squashed the commits and addressed the feedback regarding MultiSpan and the new tests

TomtheCoder2 · 2026-04-30T10:33:27Z

@rustbot ready

rustbot assigned davidtwco Nov 10, 2025

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. T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. labels Nov 10, 2025