Rid fn params of historical baggage (argument modes begone for good!)

[fmease]

FIXME(fmease): Add description.

[fmease]

@bors try

[rust-log-analyzer]

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

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

Executing "/scripts/stage_2_test_set1.sh"
+ /scripts/stage_2_test_set1.sh
PR_CI_JOB set; skipping tidy
+ '[' 1 == 1 ']'
+ echo 'PR_CI_JOB set; skipping tidy'
+ SKIP_TIDY='--skip tidy'
+ ../x.py --stage 2 test --skip tidy --skip compiler --skip src
##[group]Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.04s
##[endgroup]
downloading https://static.rust-lang.org/dist/2026-04-14/rustfmt-nightly-aarch64-unknown-linux-gnu.tar.xz
---
---- [ui] tests/ui/rfcs/rfc-2565-param-attrs/attr-without-param.rs stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/rfcs/rfc-2565-param-attrs/attr-without-param/attr-without-param.stderr`
diff of stderr:

10 LL |     fn f(#[attr]) {}
11    |                 ^ expected parameter name
12 
- error: expected argument name, found `)`
+ error: expected type or parameter name, found `)`
14   --> $DIR/attr-without-param.rs:14:17
15    |
16 LL |     fn f(#[attr]);

-    |                 ^ expected argument name
+    |                 ^ expected type or parameter name
18 
19 error: aborting due to 3 previous errors
---
To only update this specific test, also pass `--test-args rfcs/rfc-2565-param-attrs/attr-without-param.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/rfcs/rfc-2565-param-attrs/attr-without-param.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/rfcs/rfc-2565-param-attrs/attr-without-param" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "--edition=2015"
stdout: none
--- stderr -------------------------------
error: expected parameter name, found `)`
##[error]  --> /checkout/tests/ui/rfcs/rfc-2565-param-attrs/attr-without-param.rs:4:17
   |
LL |     fn f(#[attr]) {} //~ ERROR expected parameter name, found `)`
   |                 ^ expected parameter name

error: expected parameter name, found `)`
##[error]  --> /checkout/tests/ui/rfcs/rfc-2565-param-attrs/attr-without-param.rs:9:17
   |
LL |     fn f(#[attr]) {} //~ ERROR expected parameter name, found `)`
   |                 ^ expected parameter name

error: expected type or parameter name, found `)`
##[error]  --> /checkout/tests/ui/rfcs/rfc-2565-param-attrs/attr-without-param.rs:14:17
   |
LL |     fn f(#[attr]); //~ ERROR expected argument name, found `)`
   |                 ^ expected type or parameter name

error: aborting due to 3 previous errors
------------------------------------------

---- [ui] tests/ui/rfcs/rfc-2565-param-attrs/attr-without-param.rs stdout end ----

[rust-bors]

☀️ Try build successful (CI)
Build commit: 3f7e3b1 (3f7e3b175fda7edbf81081bcd9b91b73f2f7993f, parent: cb40c25f6aebb637163d26bf76a680ed6e5d1eda)

[fmease]

@craterbot check

[craterbot]

👌 Experiment pr-156157 created and queued.
🤖 Automatically detected try build 3f7e3b1
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🚧 Experiment pr-156157 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-156157 is completed!
📊 2 regressed and 1 fixed (918169 total)
📊 5228 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

Footnotes

1. re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-156157/retry-regressed-list.txt ↩

[fmease]

@craterbot run mode=check-only crates=https://crater-reports.s3.amazonaws.com/pr-156157/retry-regressed-list.txt p=1

[craterbot]

👌 Experiment pr-156157-1 created and queued.
🤖 Automatically detected try build 3f7e3b1
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🚧 Experiment pr-156157-1 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-156157-1 is completed!
📊 2 regressed and 0 fixed (4920 total)
📊 1003 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

Footnotes

1. re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-156157-1/retry-regressed-list.txt ↩

[rust-bors]

☔ The latest upstream changes (presumably #158864) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.