Mark some macros with must_use hint

[aceArt-GmbH]

Uses unstable feature #94745

Part of #126475

Marking pin::pin!() currently results in errors like

error[E0716]: temporary value dropped while borrowed
  --> /home/tux/Downloads/rust/tests/ui/coroutine/async-gen-yield-ty-is-unit.rs:13:26
   |
LL |     let async_iterator = pin!(gen_fn());
   |                          ^^^^^^^^^^^^^^- temporary value is freed at the end of this statement
   |                          |
   |                          creates a temporary value which is freed while still in use
LL |     let ctx = &mut Context::from_waker(Waker::noop());
LL |     async_iterator.poll_next(ctx);
   |     -------------- borrow later used here
   |
   = note: this error originates in the macro `pin` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider using a `let` binding to create a longer lived value
   |
LL ~     let binding = pin!(gen_fn());
LL ~     let async_iterator = binding;
   |

error: aborting due to 1 previous error

I think this is #124493?

r​? @oli-obk

[rustbot]

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[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[aceArt-GmbH]

I am not sure if all those changes are anticipated 🤔

[y21]

This seems to have regressed a lot of clippy lints/tests (for example the useless_vec lint emits no warnings at all anymore).

I'm guessing that our clippy_utils::higher::VecArgs util no longer recognizes the vec! expansion and needs to be updated

[Noratrieb]

this doesn't do anything, same for all other builtin macros. you'd need to modify the compiler

[aceArt-GmbH]

I am afraid this undergoing is way above my capabilities

[rust-log-analyzer]

The job x86_64-gnu-llvm-17 failed! Check out the build log: (web) (plain)

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

 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 46)
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 49)
 - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 61)
##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-17]
---
sccache: Starting the server...
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-17', '--enable-llvm-link-shared', '--set', 'rust.thin-lto-import-instr-limit=10', '--set', 'change-id=99999999', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--set', 'rust.lld=false', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--enable-new-symbol-mangling']
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-17/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.thin-lto-import-instr-limit := 10
configure: change-id            := 99999999
---

---- [ui] tests/ui/macros/unknown-builtin.rs stdout ----
diff of stderr:

13 LL | macro_rules! line { () => () }
15 
- error: aborting due to 2 previous errors
+ error[E0658]: use of unstable library feature 'hint_must_use'
+   --> $DIR/unknown-builtin.rs:13:5
+   --> $DIR/unknown-builtin.rs:13:5
+    |
+ LL |     std::prelude::v1::line!();
+    |
+    = note: see issue #94745 <https://github.com/rust-lang/rust/issues/94745> for more information
+    = help: add `#![feature(hint_must_use)]` to the crate attributes to enable
+    = help: add `#![feature(hint_must_use)]` to the crate attributes to enable
+    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+    = note: this error originates in the macro `std::prelude::v1::line` (in Nightly builds, run with -Z macro-backtrace for more info)
- For more information about this error, try `rustc --explain E0773`.
+ error: aborting due to 3 previous errors
+ 
+ Some errors have detailed explanations: E0658, E0773.
---
To only update this specific test, also pass `--test-args macros/unknown-builtin.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/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/macros/unknown-builtin.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/x86_64-unknown-linux-gnu/stage2" "--target=x86_64-unknown-linux-gnu" "--check-cfg" "cfg(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/x86_64-unknown-linux-gnu/test/ui/macros/unknown-builtin" "-A" "unused" "-A" "internal_features" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/macros/unknown-builtin/auxiliary"
--- stderr -------------------------------
error: cannot find a built-in macro with name `unknown`
##[error]  --> /checkout/tests/ui/macros/unknown-builtin.rs:6:1
   |
   |
LL | macro_rules! unknown { () => () } //~ ERROR cannot find a built-in macro with name `unknown`

error[E0773]: attempted to define built-in macro more than once
##[error]  --> /rustc/FAKE_PREFIX/library/core/src/macros/mod.rs:1237:5
   |
   |
note: previously defined here
  --> /checkout/tests/ui/macros/unknown-builtin.rs:9:1
   |
LL | macro_rules! line { () => () } //~ NOTE previously defined here

error[E0658]: use of unstable library feature 'hint_must_use'
##[error]  --> /checkout/tests/ui/macros/unknown-builtin.rs:13:5
   |
   |
LL |     std::prelude::v1::line!();
   |
   = note: see issue #94745 <https://github.com/rust-lang/rust/issues/94745> for more information
   = help: add `#![feature(hint_must_use)]` to the crate attributes to enable
   = help: add `#![feature(hint_must_use)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
   = note: this error originates in the macro `std::prelude::v1::line` (in Nightly builds, run with -Z macro-backtrace for more info)
error: aborting due to 3 previous errors

Some errors have detailed explanations: E0658, E0773.
For more information about an error, try `rustc --explain E0658`.

[tgross35]

Note that there are some cases where we need to be careful with hint::must_use, since it causes some surprises for lifetimes #124493. Probably good to include a test to prove that those specific circumstances don't regress for anywhere that a new must_use gets added.

edit: wow I should really read the top post before commenting, ignore me -___-

[aceArt-GmbH]

@rustbot author