Implement a lint for implicit autoref of raw pointer dereference - take 2

[Urgau]

t-lang nomination comment

This PR aims at implementing a lint for implicit autoref of raw pointer dereference, it is based on #103735 with suggestion and improvements from #103735 (comment).

The goal is to catch cases like this, where the user probably doesn't realise it just created a reference.

pub struct Test {
    data: [u8],
}

pub fn test_len(t: *const Test) -> usize {
    unsafe { (*t).data.len() }  // this calls <[T]>::len(&self)
}

Since #103735 already went 2 times through T-lang, where they T-lang ended-up asking for a more restricted version (which is what this PR does), I would prefer this PR to be reviewed first before re-nominating it for T-lang.

---

Compared to the PR it is as based on, this PR adds 3 restrictions on the outer most expression, which must either be:

1. A deref followed by any non-deref place projection (that intermediate deref will typically be auto-inserted)
2. A method call annotated with #[rustc_no_implicit_refs].
3. A deref followed by a addr_of! or addr_of_mut!. See bottom of post for details.

There are several points that are not 100% clear to me when implementing the modifications:

• "4. Any number of automatically inserted deref/derefmut calls." I as never able to trigger this. Am I missing something? Fixed
• Are "index" and "field" enough?

---

cc @JakobDegen @WaffleLapkin
r? @RalfJung

try-job: dist-various-1
try-job: dist-various-2

[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[RalfJung]

Sorry, I can't take on more reviews currently.
r? compiler
(or feel free to pick someone specific who's suited)

[Dylan-DPC]

@Urgau if you can rebase the latest conflicts we can push this forward and maybe get it reviewed by another reviewer

[Urgau]

@Dylan-DPC rebased.

@rustbot review

[bors]

⌛ Testing commit 05f2b22 with merge 5311e65...

[rust-log-analyzer]

The job x86_64-mingw-1 failed! Check out the build log: (web) (plain)

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

---- [run-make] tests\run-make\amdgpu-kd stdout ----

error: rmake recipe failed to complete
status: exit code: 1
command: "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\test\\run-make\\amdgpu-kd\\rmake.exe"
stdout: none
--- stderr -------------------------------
command failed at line 18
Command { cmd: "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\stage2\\bin\\rustc.exe" "-L" "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\test\\run-make\\amdgpu-kd\\rmake_out" "--crate-name" "foo" "--target=amdgcn-amd-amdhsa" "-Ctarget-cpu=gfx900" "--crate-type" "cdylib" "foo.rs", stdin_buf: None, stdin: None, stdout: None, stderr: None, drop_bomb: DropBomb { command: "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\stage2\\bin\\rustc.exe", defused: true, armed_location: Location { file: "D:\\a\\rust\\rust\\tests\\run-make\\amdgpu-kd\\rmake.rs", line: 12, col: 5 } }, already_executed: true }
output status: `exit code: 1`
=== STDOUT ===



=== STDERR ===
error: linking with `rust-lld` failed: exit code: 0xc0000374
  |
  = note: "rust-lld" "-flavor" "gnu" "--version-script=C:\\Users\\RUNNER~1\\AppData\\Local\\Temp\\rustcDK81Hk\\list" "--no-undefined-version" "<1 object files omitted>" "--as-needed" "-L" "C:\\Users\\RUNNER~1\\AppData\\Local\\Temp\\rustcDK81Hk\\raw-dylibs" "-Bdynamic" "--eh-frame-hdr" "-z" "noexecstack" "-L" "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\test\\run-make\\amdgpu-kd\\rmake_out" "-o" "foo.elf" "--gc-sections" "-shared"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: 

error: aborting due to 1 previous error
------------------------------------------
---
test result: FAILED. 279 passed; 1 failed; 110 ignored; 0 measured; 6 filtered out; finished in 199.20s

Some tests failed in compiletest suite=run-make mode=run-make host=x86_64-pc-windows-gnu target=x86_64-pc-windows-gnu
Build completed unsuccessfully in 2:25:17
make: *** [Makefile:124: ci-mingw-x] Error 1
  local time: Sun Apr 27 16:37:09 CUT 2025
  network time: Sun, 27 Apr 2025 16:37:09 GMT
##[error]Process completed with exit code 2.
Post job cleanup.
[command]"C:\Program Files\Git\bin\git.exe" version

[bors]

💔 Test failed - checks-actions

[Urgau]

CI error is unrelated to this PR. Seems spurious.

@bors retry

[bors]

⌛ Testing commit 05f2b22 with merge af9aa86f909dbc0990a114148a12f36a9ff4828f...

[Urgau]

@bors retry

[bors]

⌛ Testing commit 05f2b22 with merge a932eb3...

[bors]

☀️ Test successful - checks-actions
Approved by: jdonszelmann,traviscross
Pushing a932eb3 to master...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 0134651 (parent) -> a932eb3 (this PR)

Test differences

Show 1165 test diffs

Stage 1

• [ui] tests/ui/lint/implicit_autorefs.rs: [missing] -> pass (J0)

Stage 2

• [ui] tests/ui/lint/implicit_autorefs.rs: [missing] -> pass (J1)

Additionally, 1163 doctest diffs were found. These are ignored, as they are noisy.

Job group index

• J0: x86_64-gnu-llvm-19-3, x86_64-gnu-llvm-20-3
• J1: aarch64-apple, aarch64-gnu, arm-android, armhf-gnu, dist-i586-gnu-i586-i686-musl, i686-gnu-1, i686-gnu-nopt-1, i686-msvc-1, test-various, x86_64-apple-2, x86_64-gnu, x86_64-gnu-llvm-19-1, x86_64-gnu-llvm-19-2, x86_64-gnu-llvm-20-1, x86_64-gnu-llvm-20-2, x86_64-gnu-nopt, x86_64-gnu-stable, x86_64-mingw-1, x86_64-msvc-1

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard a932eb36f8adf6c8cdfc450f063943da3112d621 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. x86_64-apple-1: 8218.0s -> 6083.4s (-26.0%)
2. dist-apple-various: 6754.9s -> 8167.9s (20.9%)
3. x86_64-msvc-ext2: 6995.0s -> 5859.1s (-16.2%)
4. dist-aarch64-apple: 5175.2s -> 4666.8s (-9.8%)
5. x86_64-msvc-2: 7361.5s -> 6645.3s (-9.7%)
6. dist-x86_64-apple: 10267.2s -> 9484.6s (-7.6%)
7. dist-i686-mingw: 7817.4s -> 8250.3s (5.5%)
8. dist-powerpc64le-linux: 9389.9s -> 9859.3s (5.0%)
9. x86_64-gnu-llvm-19-1: 5337.6s -> 5100.5s (-4.4%)
10. dist-i586-gnu-i586-i686-musl: 5084.7s -> 5301.8s (4.3%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.