Proof of Concept: add #[defines] attribute and require it for all type-alias-impl-trait sites that register a hidden type

[oli-obk]

This PR is not meant to be merged (I will not be pushing changes in the next 4 months), but serves as a starting point for anyone wanting to make progress on this. It should hopefully be simple to rebase and not require you to edit 200+ tests, as these edits are done here and you can just cherry pick them out (no need for attribution, just squash as you want)

I left TODOs for everything that I think needs to be done.

• differentiate between no attribute and an empty attribute (#[defines()]), the latter opting out of impl-trait-in-assoc types automatic opaque collection in the signature (or in general, any #[defines(SomeOhterTait)] attribute behaving as an override for the default collection, too).

An interesting follow-up could also be to automatically fill in RPITs into that list in ast lowering, so that opaque_types_defined_by doesn't need to walk for RPITs anymore.

@petrochenkov can you have a look at the resolver changes so that anyone picking this up will know what to change?

[bors]

☔ The latest upstream changes (presumably #128481) made this pull request unmergeable. Please resolve the merge conflicts.

[petrochenkov]

Simple paths in attributes are not as bad as rust-lang/rfcs#3659, but still sort of meh, but probably acceptable.

We don't currently have any resolved paths (staying after macro expansion) in attributes in the proper language.
We have links in doc comments though, which are also simple paths processed during late resolution, and they also have to be kept in a separate special side table.

[petrochenkov]

Also, defines is probably a popular enough name, so the chance of regressions like #128888 may be high, if it becomes a built-in attribute.

[bors]

☔ The latest upstream changes (presumably #134492) made this pull request unmergeable. Please resolve the merge conflicts.

[oli-obk]

Blocked on #131229

[rust-log-analyzer]

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COPY host-x86_64/mingw-check/validate-toolstate.sh /scripts/
COPY host-x86_64/mingw-check/validate-error-codes.sh /scripts/

# NOTE: intentionally uses python2 for x.py so we can test it still works.
# validate-toolstate only runs in our CI, so it's ok for it to only support python3.
ENV SCRIPT TIDY_PRINT_DIFF=1 python2.7 ../x.py test \
           --stage 0 src/tools/tidy tidyselftest --extra-checks=py,cpp
# This file is autogenerated by pip-compile with Python 3.10
# by the following command:
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#    pip-compile --allow-unsafe --generate-hashes reuse-requirements.in
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#13 2.673 Building wheels for collected packages: reuse
#13 2.674   Building wheel for reuse (pyproject.toml): started
#13 2.881   Building wheel for reuse (pyproject.toml): finished with status 'done'
#13 2.882   Created wheel for reuse: filename=reuse-4.0.3-cp310-cp310-manylinux_2_35_x86_64.whl size=132718 sha256=f1d7d99e2187cfcc743e73878997db8829d4c560719802a1230bd160f7d9cfca
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#13 2.885 Installing collected packages: boolean-py, binaryornot, tomlkit, reuse, python-debian, markupsafe, license-expression, jinja2, chardet, attrs
#13 3.281 Successfully installed attrs-23.2.0 binaryornot-0.4.4 boolean-py-4.0 chardet-5.2.0 jinja2-3.1.4 license-expression-30.3.0 markupsafe-2.1.5 python-debian-0.1.49 reuse-4.0.3 tomlkit-0.13.0
#13 3.281 WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
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#13 4.299 Successfully installed distlib-0.3.9 filelock-3.16.1 platformdirs-4.3.6 virtualenv-20.28.1
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#14 [7/8] COPY host-x86_64/mingw-check/validate-toolstate.sh /scripts/
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Executing TIDY_PRINT_DIFF=1 python2.7 ../x.py test            --stage 0 src/tools/tidy tidyselftest --extra-checks=py,cpp
+ TIDY_PRINT_DIFF=1 python2.7 ../x.py test --stage 0 src/tools/tidy tidyselftest --extra-checks=py,cpp
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WARN: currently no CI rustc builds have rustc debug assertions enabled. Please either set `rust.debug-assertions` to `false` if you want to use download CI rustc or set `rust.download-rustc` to `false`.
downloading https://static.rust-lang.org/dist/2025-01-08/rustfmt-nightly-x86_64-unknown-linux-gnu.tar.xz
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fmt check
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##[error]tidy error: /checkout/compiler/rustc_ty_utils/src/opaque_types.rs:179: TODO is used for tasks that should be done before merging a PR; If you want to leave a message in the codebase use FIXME
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##[error]tidy error: /checkout/compiler/rustc_ty_utils/src/opaque_types.rs:188: TODO is used for tasks that should be done before merging a PR; If you want to leave a message in the codebase use FIXME
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##[error]tidy error: /checkout/compiler/rustc_ty_utils/src/opaque_types.rs:288: TODO is used for tasks that should be done before merging a PR; If you want to leave a message in the codebase use FIXME
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##[error]tidy error: /checkout/compiler/rustc_ast_lowering/src/lib.rs:870: TODO is used for tasks that should be done before merging a PR; If you want to leave a message in the codebase use FIXME
##[error]tidy error: /checkout/tests/ui/type-alias-impl-trait/type-alias-impl-trait-assoc-impl-trait.rs:16: line longer than 100 chars
##[error]tidy error: /checkout/tests/ui/type-alias-impl-trait/type-alias-impl-trait-assoc-impl-trait.rs:16: TODO is used for tasks that should be done before merging a PR; If you want to leave a message in the codebase use FIXME
removing old virtual environment
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10'
Requirement already satisfied: pip in ./build/venv/lib/python3.10/site-packages (24.3.1)
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Command has failed. Rerun with -v to see more details.
  local time: Fri Jan 10 09:06:17 UTC 2025
  network time: Fri, 10 Jan 2025 09:06:17 GMT
##[error]Process completed with exit code 1.
Post job cleanup.

[bors]

☔ The latest upstream changes (presumably #135519) made this pull request unmergeable. Please resolve the merge conflicts.