fix: unsoundness issue caught in recent nightly

[iamsauravsharma]

Description of changes

Return static lifetime for ValidationError and ValidationWarning so lifetime will live enough. 3.1.0 is not working with latest nightly version this PR fix that issue by returning static lifetime instead of custom lifetime
Latest nightly error message

error: lifetime may not live long enough
    --> cedar-policy/src/api.rs:1677:9
     |
1676 |     pub fn validation_errors<'b>(&self) -> impl Iterator<Item = &ValidationError<'b>> {
     |                              --  - let's call the lifetime of this reference `'1`
     |                              |
     |                              lifetime `'b` defined here
1677 |         self.validation_errors.iter()
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ method was supposed to return data with lifetime `'1` but it is returning data with lifetime `'b`

error: lifetime may not live long enough
    --> cedar-policy/src/api.rs:1682:9
     |
1681 |     pub fn validation_warnings<'b>(&self) -> impl Iterator<Item = &ValidationWarning<'b>> {
     |                                --  - let's call the lifetime of this reference `'1`
     |                                |
     |                                lifetime `'b` defined here
1682 |         self.validation_warnings.iter()
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ method was supposed to return data with lifetime `'1` but it is returning data with lifetime `'b`

error: lifetime may not live long enough
    --> cedar-policy/src/api.rs:1920:5
     |
1914 |   pub fn confusable_string_checker<'a, 'b>(
     |                                        -- lifetime `'b` defined here
...
1920 | /     cedar_policy_validator::confusable_string_checks(templates.map(|t| &t.ast))
1921 | |         .map(std::convert::Into::into)
     | |______________________________________^ returning this value requires that `'b` must outlive `'static`

error: could not compile `cedar-policy` (lib) due to 3 previous errors

Checklist for requesting a review

The change in this PR is (choose one, and delete the other options):

• A bug fix or other functionality change requiring a patch to cedar-policy.

I confirm that this PR (choose one, and delete the other options):

• Updates the "Unreleased" section of the CHANGELOG with a description of my change (required for major/minor version bumps).

I confirm that cedar-spec (choose one, and delete the other options):

• Does not require updates because my change does not impact the Cedar formal model or DRT infrastructure.

Disclaimer

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[iamsauravsharma]

I have already created issue at rust-lang/rust#122230 which informs it is expected breakage so this PR fixes issue early for unsoundess. For more information visit issue

[john-h-kastner-aws]

Thanks for catching this.

We originally wrote it how we did because returning a static lifetime caused some dependencies builds to break due to something around lifetime inference, but (at least according to CI) this seems to work.

[iamsauravsharma]

@john-h-kastner-aws I have removed some unnecessary lifetimes to solve above issue. All lifetimes are not required to create above changed struct. This solve issue by removing lifetime altogether

[john-h-kastner-aws]

I believe that would be a breaking change for any user who references the types with explicit lifetimes. We can take that change on main, but will likely patch 3.1 with your original commit.

[iamsauravsharma]

Ya you are correct. I think I will only add original changes to this PR and create new PR for next breaking changes

[iamsauravsharma]

@john-h-kastner-aws I have reverted to original fix in this PR and created another PR #715 for breaking change