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Add lint for recursive default impls #128737

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Add lint for recursive default impls #128737

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mj10021
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@mj10021 mj10021 commented Aug 6, 2024

Fixes #128421, where it was pointed out that recursion in default impls can be confusing and always results in failure.

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@rustbot 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 Aug 6, 2024
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I don't think this should be a new lint. We already have a lint for when we detect recursive calls, and we can change the wording for that lint if we detect that it's a recursive Default invocation.

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compiler-errors reviewed Aug 6, 2024
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compiler/rustc_lint_defs/src/builtin.rs Outdated
/// default struct for this field. This will always lead to an infinite loop
/// so it is denied.
pub RECURSIVE_DEFAULT_IMPL,
Deny,
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This needs T-lang approval if it's going to be a Deny lint.

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mj10021 commented Aug 6, 2024

I don't think this should be a new lint. We already have a lint for when we detect recursive calls, and we can change the wording for that lint if we detect that it's a recursive Default invocation.

Do you think that it makes sense for the Self { ..Default::default() } case to be denied since it is a guaranteed infinite loop or it is too specific off a case to warrant special treatment?

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mj10021 commented Aug 6, 2024

@rustbot label +T-Lang

@rustbot rustbot added the T-lang Relevant to the language team, which will review and decide on the PR/issue. label Aug 6, 2024
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yeah, I think it's better to change the wording for existing lint for this specific scenario.

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@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 24, 2024
@compiler-errors compiler-errors self-assigned this Aug 24, 2024
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bors commented Sep 23, 2024

☔ The latest upstream changes (presumably #130724) made this pull request unmergeable. Please resolve the merge conflicts.

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From wg-triage. Do you have update on this PR?

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mj10021 commented Oct 31, 2024

@mj10021 From wg-triage. Do you have update on this PR?

Oops, this got away from me, will update the PR shortly

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mj10021 commented Nov 5, 2024

Does this look more like the type of note that was in mind?

@Dylan-DPC Dylan-DPC added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Nov 6, 2024
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@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 21, 2024
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mj10021 commented Nov 24, 2024

@rustbot review

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Nov 24, 2024
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I don't think that this change carries enough benefit, especially b/c I don't believe we can actually tell we're actually in a FRU to make this note accurate.

tests/ui/lint/lint-unconditional-recursion.stderr
@@ -122,6 +122,7 @@ LL | let x = Default::default();
| ------------------ recursive call site
|
= help: a `loop` may express intention better if this is on purpose
= help: calling `..Default::default()` in a `Default` implementation leads to infinite recursion, and does not initialize the fields of a struct or enum
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This is evidence of false positives for this lint.

@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 16, 2024
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r? compiler

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bors commented Dec 18, 2024

☔ The latest upstream changes (presumably #134470) made this pull request unmergeable. Please resolve the merge conflicts.

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@mj10021 any updates on this pr? thanks

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mj10021 commented Mar 3, 2025

@mj10021 any updates on this pr? thanks

Sorry, I thought the PR was rejected, are these changes still wanted?

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Recursive ..Default::default() overflows
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@mj10021 @rustbot @rust-log-analyzer @chenyukang @bors @alex-semenyuk @compiler-errors @Dylan-DPC @wesleywiser