feat(uri): make Authority/PathAndQuery::from_static const

[WaterWhisperer]

Changes

• Authority::from_static and PathAndQuery::from_static are now const.
• Both perform compile-time validation equivalent to their runtime counterparts using byte-wise scanning.
• For const panics on invalid input, uses an out-of-bounds indexing trick compatible with MSRV 1.49 .

Explanation

Uri::from_static remains non-const. Two blockers under MSRV 1.49:

1. Const slicing of &'static str is unavailable, but Uri parsing requires slicing the input into scheme/authority/path+query.
2. Non-standard schemes use Box, which requires allocation not allowed in const fn.

Tests

• cargo test passed.
• Doc tests for const usage included implicitly via examples.

Related issue

Partially fixes #750

[WaterWhisperer]

Hello @seanmonstar

This PR has been open for some time, and I'd like to politely request a review (mainly marking Authority/PathAndQuery::from_static as const, so it can be used in const contexts). Thanks!

[seanmonstar]

Thanks for the PR! I think the objective is worthy, for sure!

I do worry about having parsing be duplicated in two different forms, it's possible for one to change without the other. Is it possible to make this change while keeping only one version of the parsing code?

[WaterWhisperer]

Thanks for the PR! I think the objective is worthy, for sure!

I do worry about having parsing be duplicated in two different forms, it's possible for one to change without the other. Is it possible to make this change while keeping only one version of the parsing code?

@seanmonstar Thanks for the feedback!

IMO the clean solution is to extract the validation into a shared const helper function that both from_static and parse() can call. This way there's only one source of truth for the validation logic.

The refactor would look like:

1. Extract validation into const fn validate_authority_bytes(bytes: &[u8]) -> bool
2. from_static calls it and panics if invalid (const-compatible)
3. parse() calls it and converts the bool to a Result

I can implement this if it sounds good to you. Or do you have any good ideas?

[seanmonstar]

I think that makes sense, can the const fn validate() return an enum so we can provide better error messages about why it failed? Otherwise, sounds good to me.

[seanmonstar]

(I can address the MSRV issues in a separate PR.)

[seanmonstar]

I've fixed the MSRV, raising it to 1.57. If you want to change from using the weird panic syntax to just a plain string, we can merge this in for the next release :)

[WaterWhisperer]

I've fixed the MSRV, raising it to 1.57. If you want to change from using the weird panic syntax to just a plain string, we can merge this in for the next release :)

Thanks!

[seanmonstar]

Awesome, nice work! One last thought when I reviewed this again, could you keep the code comment that explained what was happening, or place them where they now belong?

[seanmonstar]

Beautiful, thanks!