Revert "Teach parser to understand fake anonymous enum syntax" and related commits

[compiler-errors]

anonymous enum types are currently ambiguous in positions like:

• | operator: a as fn() -> B | C
• closure args: |_: as fn() -> A | B

I first tried to thread around RecoverAnonEnum into all these positions, but the resulting complexity in the compiler is IMO not worth it, or at least worth a bit more thinking time. In the mean time, let's revert this syntax for now, so we can go back to the drawing board.

Fixes #107461

cc: @estebank @cjgillot #106960

---

Squashed revert commits:

Revert "review comment: Remove AST AnonTy"

This reverts commit 020cca8.

Revert "Ensure macros are not affected"

This reverts commit 12d18e4.

Revert "Emit fewer errors on patterns with possible type ascription"

This reverts commit c847a01.

Revert "Teach parser to understand fake anonymous enum syntax"

This reverts commit 2d82420.

[rustbot]

r? @oli-obk

(rustbot has picked a reviewer for you, use r? to override)

[estebank]

@compiler-errors can you add tests for those ambiguous case, in case someone tries to do this again?

r=me

[compiler-errors]

I did in 859b14ce7d469bc1af3ee396fd8e91b7b2e20d6f 😸

@bors r=estebank

[bors]

📌 Commit 859b14ce7d469bc1af3ee396fd8e91b7b2e20d6f has been approved by estebank

It is now in the queue for this repository.

[estebank]

I first tried to thread around RecoverAnonEnum into all these positions, but the resulting complexity in the compiler is IMO not worth it, or at least worth a bit more thinking time.

I think that instead we can rely on global Parser state to control when these kinds of anon enums can be detected. I have global state, but it is a natural communication mechanism for the parser :-/

[estebank]

I just noticed that the type ascription in patterns change is also being reverted here. Would you mind relanding those on their own?

[compiler-errors]

@estebank oh yes, let me re-teach the compiler those really quick. Sorry, I totally overlooked those because they weren't their own commit 😅

[compiler-errors]

Added a few more test cases that shouldn't be broken when this PR is re-attempted.

@bors r=estebank

[bors]

📌 Commit daf382895f3fcd635c95bf2a95114f5ed6dc9e61 has been approved by estebank

It is now in the queue for this repository.

[bors]

☔ The latest upstream changes (presumably #107536) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

🔒 Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming self is your fork and upstream is this repository, you can resolve the conflict following these steps:

1. git checkout anon-enum-tys-are-ambiguous (switch to your branch)
2. git fetch upstream master (retrieve the latest master)
3. git rebase upstream/master -p (rebase on top of it)
4. Follow the on-screen instruction to resolve conflicts (check git status if you got lost).
5. git push self anon-enum-tys-are-ambiguous --force-with-lease (update this PR)

You may also read Git Rebasing to Resolve Conflicts by Drew Blessing for a short tutorial.

Please avoid the "Resolve conflicts" button on GitHub. It uses git merge instead of git rebase which makes the PR commit history more difficult to read.

Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how Cargo.lock conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

Removing tests/ui/parser/fake-anon-enums-in-macros.rs
Removing tests/ui/parser/anon-enums.stderr
Removing tests/ui/parser/anon-enums.rs
Auto-merging compiler/rustc_parse/src/parser/ty.rs
CONFLICT (content): Merge conflict in compiler/rustc_parse/src/parser/ty.rs
Automatic merge failed; fix conflicts and then commit the result.

[compiler-errors]

@bors r=estebank

[bors]

📌 Commit 250f530 has been approved by estebank

It is now in the queue for this repository.

[bors]

🌲 The tree is currently closed for pull requests below priority 50. This pull request will be tested once the tree is reopened.

[bors]

☔ The latest upstream changes (presumably #105670) made this pull request unmergeable. Please resolve the merge conflicts.

[compiler-errors]

This is bitrotty, but also P-critical 😓

@bors p=1

[compiler-errors]

@bors r=estebank

[bors]

📌 Commit 39db65c has been approved by estebank

It is now in the queue for this repository.

[bors]

⌛ Testing commit 39db65c with merge 97872b7...

[bors]

☀️ Test successful - checks-actions
Approved by: estebank
Pushing 97872b7 to master...

[bors]

☀️ Test successful - checks-actions
Approved by: estebank
Pushing 97872b7 to master...

[rust-timer]

Finished benchmarking commit (97872b7): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.9%	[1.6%, 2.3%]	2
Improvements ✅ (primary)	-1.4%	[-1.4%, -1.4%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.4%	[-1.4%, -1.4%]	1

Cycles

This benchmark run did not return any relevant results for this metric.