Add new `try_from_instead_of_from_str` lint by GuillaumeGomez · Pull Request #17030 · rust-lang/rust-clippy

GuillaumeGomez · 2026-05-18T01:09:50Z

One big thing: I'm not sure if the lint name is good, so very much up to debate.

changelog: Add new try_from_instead_of_from_str lint

rustbot · 2026-05-18T01:09:55Z

rustbot has assigned @Jarcho.
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github-actions · 2026-05-18T01:19:39Z

Lintcheck changes for 2b63015

Lint	Added	Removed	Changed
`clippy::try_from_instead_of_from_str`	1	0	0

This comment will be updated if you push new changes

Jarcho

You also have to check if the error type is using the lifetime since FromStr can't capture there either. Also please make sure to put the HIR matching code before item identification code. It's generally faster to check since it doesn't got through the query system.

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GuillaumeGomez · 2026-06-03T16:15:44Z

Thanks for the suggestions @Jarcho. Hopefully I caught all lifetime cases. Updated the code too as you suggested.

@rustbot ready

GuillaumeGomez · 2026-06-15T16:19:02Z

Handled the lifetimes, moved the params length condition upper and added tests. Ready for a new review.

@rustbot ready

GuillaumeGomez · 2026-06-17T21:40:40Z

Applied suggestions.

GuillaumeGomez · 2026-06-24T12:55:51Z

Applied suggestion to only look at where predicates.

Jarcho · 2026-06-24T20:20:12Z

@rustbot label lint-nominated

Forgot to do this earlier.

rustbot · 2026-06-24T20:20:18Z

This lint has been nominated for inclusion.

A FCP topic has been created on Zulip.

Jarcho · 2026-06-24T20:36:44Z

One last case from the lintcheck results: we shouldn't lint if FromStr is already implemented. Should just need a single call to implements_trait. There isn't a diagnostic item for FromStr so you can add it to clippy_utils::paths until a diagnostic item is added.

GuillaumeGomez · 2026-06-25T09:45:35Z

Ah indeed. ^^'

Adding it as well.

Jarcho · 2026-07-06T08:14:08Z

+    ///
+    /// ### Why is this bad?
+    ///
+    /// It is more idiomatic to use `FromStr`.


This needs to be significantly fleshed out. FromStr is only more idiomatic for parsing the string, not for all conversions. e.g. something like ArrayStr<const N: usize> would make more sense using TryFrom<&str> even though FromStr works.

View changes since the review

I added more information.

This still needs an explanation of why it's idiomatic, not just a claim that it is. I'm not sure why you added a note about constants since that makes no difference between the two traits.

Rewrote the explanation.

The latest version still leaves the reason implied from the mention of str::parse rather than stated outright. Specifically it uses "the intent of the conversion is more explicit" without stating what intent is made more explicit. I would word it more like: "FromStr is the idiomatic trait for parsing a string and should be preferred over TryFrom when doing so. Implementing FromStr allows the the use str:parse to make the intent of the conversion clearer at the conversion site."

Adding a "Known problems" section explaining the lint doesn't pick up on the intent of the conversion would also help. You can use a type like ArrayString as an example where FromStr doesn't express the intent of the conversion (a length limit).

rustbot · 2026-07-15T13:55:36Z

This PR was rebased onto a different master 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.

GuillaumeGomez · 2026-07-27T12:10:41Z

Forgot to toggle the label...

@rustbot ready

Jarcho · 2026-07-28T00:55:44Z

+            && let Some(generics) = snippet_opt(cx, imp.generics.span)
+            && let Some(self_ty) = snippet_opt(cx, imp.self_ty.span)
+        {
+            span_lint_and_sugg(


Would be nice to have a second help message with "or implement both FromStr and TryFrom" to help point out that it doesn't have to be one or the other.

View changes since the review

Huuuum... I'm not sure we want to multiply the trait impls for a somewhat similar purpose.

I was thinking of cases where you can't remove necessarily remove the TryFrom impl. Thinking about this the lint should be using avoid_breaking_exported_api. So for reachable type this could use suggest to either replace the old impl or only add the new one. When avoid_breaking_exported_api the suggestion to replace should be suppressed since it's not a viable option anymore.

I'll make the suggestion MachineApplicable only in case avoid_breaking_exported_api is disabled.

GuillaumeGomez · 2026-07-28T13:14:03Z

Updated the description. Not sure about the second suggestion message though.

GuillaumeGomez · 2026-07-31T22:53:34Z

avoid_breaking_exported_api is now taken into account. Thanks a lot for all that and sorry for all the back and forth.

rustbot · 2026-08-12T14:34:07Z

☔ The latest upstream changes (possibly #17552) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot assigned Jarcho May 18, 2026

rustbot added needs-fcp PRs that add, remove, or rename lints and need an FCP S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels May 18, 2026

GuillaumeGomez mentioned this pull request May 18, 2026

Suggest impl FromStr instead of TryFrom<&str> #14522

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GuillaumeGomez force-pushed the try_from_instead_of_from_str branch from 4acca7d to a9d577c Compare June 7, 2026 20:54

GuillaumeGomez force-pushed the try_from_instead_of_from_str branch from a9d577c to 44e112d Compare June 15, 2026 16:17

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GuillaumeGomez force-pushed the try_from_instead_of_from_str branch from 44e112d to 0398277 Compare June 16, 2026 12:13

GuillaumeGomez force-pushed the try_from_instead_of_from_str branch from 8b54996 to 384a8a6 Compare June 17, 2026 21:47

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GuillaumeGomez force-pushed the try_from_instead_of_from_str branch from f761827 to 3fca089 Compare June 25, 2026 13:36

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Add new try_from_instead_of_from_str lint

d738982

GuillaumeGomez force-pushed the try_from_instead_of_from_str branch from b4d0f69 to d738982 Compare July 28, 2026 13:11

GuillaumeGomez force-pushed the try_from_instead_of_from_str branch from 859cd28 to 23695e8 Compare July 31, 2026 18:05

Take into account avoid_breaking_exported_api

2b63015

GuillaumeGomez force-pushed the try_from_instead_of_from_str branch from 23695e8 to 2b63015 Compare July 31, 2026 18:08

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GuillaumeGomez commented Jun 3, 2026

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