Add Removed Library Features API and tests (unstable_removed)

[nilotpal-n7]

Add Removed Library Features API and tests (unstable_removed)

Summary

This PR introduces explicit test coverage for removed library features,
ensuring that rustc reports the correct diagnostic (E0557) when such a
feature is used.

A dummy feature unstable_removed was added to exercise the mechanism.
The error message now includes both the version in which the feature was
removed (1.89.0) and the removal reason (test_reason).

Changes

1. Compiler Internals

• Extended rustc_session::Session to carry a removed_features: Vec<RemovedFeature>.
• Integrated removed feature handling so diagnostics include extra details (since + reason).

2. Diagnostics

• When a removed feature is encountered, rustc now emits:

E0557: feature has been removed

with additional notes for the removal version and reason.

3. New UI Test

• Added tests/ui/stability-attribute/removed-library-feature.rs:

// check-fail
// compile-flags: -Z unstable-options

#![feature(unstable_removed)] //~ ERROR feature has been removed

fn main() {}

• Added corresponding .stderr file to assert:

error[E0557]: feature has been removed
  --> $DIR/removed-library-feature.rs:4:12
   |
LL | #![feature(unstable_removed)]
   |            ^^^^^^^^^^^^^^^^ feature has been removed
   |
   = note: removed in 1.89.0
   = note: test_reason

Motivation

• Ensures removed feature diagnostics are tested and stable, preventing regressions in future compiler changes.
• Improves clarity by surfacing both the removal version and the reason.

Testing

• Ran the UI test suite with:

./x test tests/ui/stability-attribute/removed-library-feature.rs -- --bless

• Verified that diagnostics match expected output exactly.
• Confirmed no regressions in other tests.

Future Work

• Extend coverage to other removed features if necessary.
• Ensure all removed feature diagnostics include metadata consistently.

Issue: #141617

[rustbot]

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann

Some changes occurred to constck

cc @fee1-dead

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann

[rustbot]

r? @petrochenkov

rustbot has assigned @petrochenkov.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[jdonszelmann]

r? jdonszelmann

[jdonszelmann]

(btw, we usually rebase onto master, not merge master into feature branches. we can't merge like this)

[rustbot]

Some changes occurred in src/tools/cargo

cc @ehuss

[jdonszelmann]

maybe just error out in this case instead of putting a magic symbol in. If you do want to continue, return None but using sym::err doesn't seem like a great idea

[jdonszelmann]

This comment is not yet addressed

[rustbot]

⚠️ Warning ⚠️

• Some commits in this PR modify submodules.

  If this was not intentional, see I changed a submodule on accident in the rustc dev guide.

[jdonszelmann]

@rustbot author (I'll review more when CI passes)

[rustbot]

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[fee1-dead]

I would recommend using the concat_idents feature to test the #![unstable_removed] once that gets actually implemented

[jdonszelmann]

Adding a logging system is not a fix for an ICE, and we don't just print things in the middle of the compiler. (In response to your latest commit). It seems, though I might be wrong, that you use a lot of AI generated code, or at the very least submit code that is not ready to be part of the compiler. There are many things I could comment on but in the current state I don't want to spend any more time on it since there are still many very obvious problems. I recommend you review your own diff by yourself and make another pass on it yourself. However, if after that it's still like this I'm going to close this PR

[jdonszelmann]

@rustbot author

[RalfJung]

I also see no reason why we would even need a new StabilityLevel to deal with the remaining part of #141617. Renamed language features also don't have that I think?