Implement RFC 3678: Final trait methods

[mu001999]

Tracking: #131179

This PR is based on #130802, with some minor changes and conflict resolution.

Futhermore, this PR excludes final methods from the vtable of a dyn Trait.

And some excerpt from the original PR description:

Implements the surface part of rust-lang/rfcs#3678.

I'm using the word "method" in the title, but in the diagnostics and the feature gate I used "associated function", since that's more accurate.

cc @joshtriplett

[rustbot]

Some changes occurred in compiler/rustc_builtin_macros/src/autodiff.rs

cc @ZuseZ4

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[rustbot]

r? @fee1-dead

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[fmease]

Could you mark errs as a coauthor in all 6 commits, I think that's only fair. Thanks! :)

Namely: Co-authored-by: Michael Goulet <michael@errs.io>

[mu001999]

@fmease Done. Thanks for the reminder! :)

[joshtriplett]

What it doesn't implement are any optimizations that can be done on final trait methods, such as excluding them from the vtable of a dyn Trait.

Does this implement the requirement that final methods don't prevent a trait from being dyn-compatible?

[mu001999]

Does this implement the requirement that final methods don't prevent a trait from being dyn-compatible?

Implemented now :). Also, updated the PR description.

[rustbot]

This PR was rebased onto a different main 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.

[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

REPOSITORY                                   TAG       IMAGE ID       CREATED       SIZE
ghcr.io/dependabot/dependabot-updater-core   latest    bcec0b4e062b   10 days ago   783MB
=> Removing docker images...
Deleted Images:
untagged: ghcr.io/dependabot/dependabot-updater-core:latest
untagged: ghcr.io/dependabot/dependabot-updater-core@sha256:b662be51f7b8ef7e2c8464428f14e49cb79c36aa9afb7ecb9221dfe0f507050c
deleted: sha256:bcec0b4e062b5ffe11cc1c2729558c0cd96621c0271ab5e97ff3a56e0c25045a
deleted: sha256:64e147d5e54d9be8b8aa322e511cda02296eda4b8b8d063c6a314833aca50e29
deleted: sha256:5cba409bb463f4e7fa1a19f695450170422582c1bc7c0e934d893b4e5f558bc6
deleted: sha256:cddc6ebd344b0111eaab170ead1dfda24acdfe865ed8a12599a34d338fa8e28b
deleted: sha256:2412c3f334d79134573cd45e657fb6cc0abd75bef3881458b0d498d936545c8d
---
tests/ui/drain_collect.fixed ... ok
tests/ui/duplicate_underscore_argument.rs ... ok
tests/ui/drop_non_drop.rs ... ok
tests/ui/duplicated_attributes.rs ... ok
tests/ui/duration_suboptimal_units_days_weeks.rs ... ok
tests/ui/duration_suboptimal_units.rs ... ok
tests/ui/double_parens.fixed ... ok
tests/ui/duration_subsec.rs ... ok
tests/ui/duration_suboptimal_units_days_weeks.fixed ... ok
tests/ui/duration_suboptimal_units.fixed ... ok
tests/ui/duration_subsec.fixed ... ok
tests/ui/eager_transmute.rs ... ok
tests/ui/elidable_lifetime_names.rs ... ok
tests/ui/else_if_without_else.rs ... ok
tests/ui/empty_docs.rs ... ok
---
..............................................     (146/146)

======== tests/rustdoc-gui/search-filter.goml ========

[ERROR] line 48: Error: The CSS selector "#search-tabs .count.loading" still exists: for command `wait-for-false: "#search-tabs .count.loading"`
    at <file:///checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc-gui/doc/test_docs/index.html?search=test>

======== tests/rustdoc-gui/search-result-display.goml ========

[WARNING] line 39: Delta is 0 for "x", maybe try to use `compare-elements-position` instead?

[mu001999]

Spurious failure