reduce the amount of panics in `{TokenStream, Literal}::from_str` calls #147859

cyrgani · 2025-10-18T20:13:31Z

Before this PR, calling TokenStream::from_str or Literal::from_str with an invalid argument would always cause a compile error, even if the TokenStream is not used afterwards at all.
This PR changes this so it returns a LexError instead in some cases.

This is very theoretically a breaking change, but the doc comment on the impl already says

/// NOTE: some errors may cause panics instead of returning `LexError`. We reserve the right to
/// change these errors into `LexError`s later.

Fixes some cases of #58736.

rustbot · 2025-10-18T20:13:34Z

rust-analyzer is developed in its own repository. If possible, consider making this change to rust-lang/rust-analyzer instead.

cc @rust-lang/rust-analyzer

rustbot · 2025-10-18T20:13:36Z

r? @davidtwco

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cyrgani · 2025-10-18T21:47:52Z

@rustbot author

rustbot · 2025-10-18T21:47:56Z

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

cyrgani · 2025-10-19T10:12:43Z

@rustbot ready

tests/ui/proc-macro/invalid-punct-ident-4.rs

cyrgani · 2025-10-23T14:03:39Z

This does not fix #58736 entirely yet:

TokenStream::from_str("0b2");

is still a compile error because it internally calls literal_from_str, which then emits the diagnostic.

davidtwco · 2025-10-25T11:33:55Z

I'm not familiar enough with this part of the compiler

r? compiler

add larger test for `proc_macro` `FromStr` implementations Currently, there are only few tests that check the output of `TokenStream::from_str` and `Literal::from_str` (which is somewhat understandable as the rustc implementation just delegates these calls to the parser). In preparation for both the standalone backend (rust-lang#130856) which will probably need to reimplement this logic as well as for removing panics from these functions (rust-lang#58736), this PR adds a test which shows the various messy ways of how these functions report errors and the return values for successful parses. Followup PRs such as rust-lang#147859 will change more and more of these "diagnostic + error"s into `LexErrors`. The test structure with the extra module is used to allow reusing it later easily for the standalone backend.

bors · 2025-12-01T18:24:22Z

☔ The latest upstream changes (presumably #149499) made this pull request unmergeable. Please resolve the merge conflicts.

JonathanBrouwer · 2025-12-15T13:33:20Z

I think there is still work to do in improving the error messages, but this can happen in future PRs, this is already a big improvement.
One final concern I have: Are there any stability guarantees for the Display implementation of LexError? I'm assuming there wouldn't (or at least shouldn't) be but not exactly sure if/where this is documented.
This PR changes the Display implementation of the type & I'd like to leave the option of improving these messages later open.

JonathanBrouwer · 2025-12-15T17:44:35Z

@rustbot author

JonathanBrouwer · 2025-12-22T20:56:11Z

Started a thread here to discuss this #t-libs > Questions for a PR I'm reviewing @ 💬

JonathanBrouwer

From a T-compiler perspective this code looks fine, but I'm not super familiar with this code and feel like T-libs should also have a say about it, so will re-assign.
r? libs

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JonathanBrouwer · 2026-01-27T16:27:06Z

compiler/rustc_errors/src/diagnostic.rs

@@ -1378,6 +1378,13 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
        drop(self);


Will put the text from my comment above in a discussion so it is not missed:

One final concern I have: Are there any stability guarantees for the Display implementation of LexError? I'm assuming there wouldn't (or at least shouldn't) be but not exactly sure if/where this is documented.
This PR changes the Display implementation of the type & I'd like to leave the option of improving these messages later open.

joboet · 2026-01-27T19:20:51Z

I'm not very familiar with proc_macro.

r? @petrochenkov

rustbot · 2026-01-27T21:29:16Z

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.

rust-bors · 2026-02-09T22:46:54Z

☔ The latest upstream changes (presumably #152399) made this pull request unmergeable. Please resolve the merge conflicts.

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cyrgani changed the title ~~replace TokenStream::from_str panics with LexErrors~~ reduce the amount of panics in {TokenStream, Literal}::from_str calls Oct 29, 2025

cyrgani mentioned this pull request Nov 4, 2025

add larger test for proc_macro FromStr implementations #148505

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reduce the amount of panics in {TokenStream, Literal}::from_str calls

519a3f7

rust-cloud-vms bot force-pushed the nonfatal-tokenstream-parse branch from 33ff2a3 to 519a3f7 Compare January 27, 2026 21:29

		@@ -1378,6 +1378,13 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
		drop(self);

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reduce the amount of panics in `{TokenStream, Literal}::from_str` calls #147859

reduce the amount of panics in `{TokenStream, Literal}::from_str` calls #147859

cyrgani commented Oct 18, 2025 •

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