Revert "Make PROC_MACRO_DERIVE_RESOLUTION_FALLBACK a hard error"
This reverts commit 7d82cadd97 aka PR #84022
I am doing this to buy us some time with respect to issue #106337 w.r.t. the 1.67 release.
Remap paths in UI tests by default
If you think this needs further discussions / something RFC-like, please let me know the best forum for that.
This PR runs UI tests with a remapped "src base" directory by default.
Why? Because some UI tests currently depend on the length of the absolute path to the `src/test/ui` directory. Remapping makes the tests independent of the absolute path.
The path to the source file (which is absolute on CI) is part of the type name of closures. `rustc` diagnostic output depends on the length of type names (long type names are truncated). So a long absolute path leads to long closure type names, which leads to truncation and changed diagnostics.
(I initially tried just disabling type name truncation, but that made some error messages stupid long (thousands of characters, IIRC)).
Additional changes:
* All boolean `compiletest` directives now support explicit `no-` versions to disable them.
* Adapt existing tests when necessary:
* Disable remapping for individual tests that fail with it enabled (when there's no obvious alternative fix).
* For tests that already check something remapping related switch to the new option unless we gain something significant by keeping the manual remap.
Passed Windows CI in https://github.com/rust-lang/rust/actions/runs/3933100590
Update `rental` hack to work with remapped paths.
This PR simply switches to an already-existing helper instead of hard-coding a specific enum variant. The new revision of the test fails without the other changes in this PR.
Context: I'm exploring running UI tests with remapped paths by default in #105924 and the rental test was one of the ones that failed.
This may also be useful in the context of https://github.com/rust-lang/rfcs/pull/3127 ("New rustc and Cargo options to allow path sanitisation by default").
