Add explanatory message for [#must_use] in ops

[chenyukang]

Fixes #103320

[rustbot]

r? @m-ou-se

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[rustbot]

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

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[chenyukang]

r? rust-lang/library

[rustbot]

Team or group rust-lang/library not found.

rust-lang team names can be found at https://github.com/rust-lang/team/tree/master/teams.
Reviewer group names can be found in triagebot.toml in this repo.

[chenyukang]

r? rust-lang/libs

[compiler-errors]

@chenyukang can you change this to be a bit more in-line with the unused message for operators?

warning: unused arithmetic operation that must be used
 --> src/main.rs:4:5
  |
4 |     1 + 2;
  |     ^^^^^ the arithmetic operation produces a value
  |
  = note: `#[warn(unused_must_use)]` on by default
help: use `let _ = ...` to ignore the resulting value
  |
4 |     let _ = 1 + 2;
  |     +++++++

[chenyukang]

@chenyukang can you change this to be a bit more in-line with the unused message for operators?

warning: unused arithmetic operation that must be used
 --> src/main.rs:4:5
  |
4 |     1 + 2;
  |     ^^^^^ the arithmetic operation produces a value
  |
  = note: `#[warn(unused_must_use)]` on by default
help: use `let _ = ...` to ignore the resulting value
  |
4 |     let _ = 1 + 2;
  |     +++++++

Updated, thanks!

[jyn514]

r? @compiler-errors

[rustbot]

rustc_error_messages was changed

cc @davidtwco, @compiler-errors, @JohnTitor, @estebank, @TaKO8Ki

[compiler-errors]

Looks fine to me, any follow-ups can be iterated on in another PR I think.

@bors r+

[bors]

📌 Commit 6e84f7d has been approved by compiler-errors

It is now in the queue for this repository.

[bors]

⌛ Testing commit 6e84f7d with merge b0ad27afaac9feafd139ce80cdddee23d7c251a4...

[bors]

💔 Test failed - checks-actions

[compiler-errors]

@bors r+

[bors]

📌 Commit cb55d10 has been approved by compiler-errors

It is now in the queue for this repository.

[bors]

⌛ Testing commit cb55d10 with merge 43cffee12404cb6ea088bd1e9cd2ba72f5bbb4a3...

[bors]

💔 Test failed - checks-actions

[estebank]

@bors retry

[bors]

⌛ Testing commit cb55d10 with merge 044a28a...

[chenyukang]

Seems CI is not stable, building get an error:

[2627/3025] Linking CXX static library lib\libLLVMWebAssemblyDisassembler.a
FAILED: lib/libLLVMWebAssemblyDisassembler.a 
cmd.exe /C "cd . && "C:\Program Files\CMake\bin\cmake.exe" -E rm -f lib\libLLVMWebAssemblyDisassembler.a && D:\a\rust\rust\mingw64\bin\ar.exe qc lib\libLLVMWebAssemblyDisassembler.a  lib/Target/WebAssembly/Disassembler/CMakeFiles/LLVMWebAssemblyDisassembler.dir/WebAssemblyDisassembler.cpp.obj && D:\a\rust\rust\mingw64\bin\ranlib.exe lib\libLLVMWebAssemblyDisassembler.a && cd ."
D:\a\rust\rust\mingw64\bin\ranlib.exe: could not create temporary file whilst writing archive: no more archived files

[2628/3025] Linking CXX static library lib\libLLVMSelectionDAG.a
[2629/3025] Building C object tools/llvm-c-test/CMakeFiles/llvm-c-test.dir/object.c.obj
[2630/3025] Building C object tools/llvm-c-test/CMakeFiles/llvm-c-test.dir/helpers.c.obj
[2631/3025] Linking CXX executable bin\llvm-bcanalyzer.exe
[2632/3025] Linking CXX executable bin\llvm-profdata.exe
[2633/3025] Linking CXX executable bin\llvm-as.exe
[2634/3025] Linking CXX static library lib\libLLVMPasses.a
ninja: build stopped: subcommand failed.
thread 'main' panicked at '
command did not execute successfully, got: exit code: 1

build script failed, must exit now', C:\Users\runneradmin\.cargo\registry\src\index.crates.io-6f17d22bba15001f\cmake-0.1.48\src\lib.rs:975:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
	finished in 229.322 seconds

[bors]

☀️ Test successful - checks-actions
Approved by: compiler-errors
Pushing 044a28a to master...

[rust-log-analyzer]

The job x86_64-mingw-2 failed! Check out the build log: (web) (plain)

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

[2625/3025] Linking CXX static library lib\libLLVMDWARFLinker.a
[2626/3025] Building C object tools/llvm-c-test/CMakeFiles/llvm-c-test.dir/disassemble.c.obj
[2627/3025] Linking CXX static library lib\libLLVMWebAssemblyDisassembler.a
FAILED: lib/libLLVMWebAssemblyDisassembler.a 
cmd.exe /C "cd . && "C:\Program Files\CMake\bin\cmake.exe" -E rm -f lib\libLLVMWebAssemblyDisassembler.a && D:\a\rust\rust\mingw64\bin\ar.exe qc lib\libLLVMWebAssemblyDisassembler.a  lib/Target/WebAssembly/Disassembler/CMakeFiles/LLVMWebAssemblyDisassembler.dir/WebAssemblyDisassembler.cpp.obj && D:\a\rust\rust\mingw64\bin\ranlib.exe lib\libLLVMWebAssemblyDisassembler.a && cd ."
D:\a\rust\rust\mingw64\bin\ranlib.exe: could not create temporary file whilst writing archive: no more archived files
[2628/3025] Linking CXX static library lib\libLLVMSelectionDAG.a
[2629/3025] Building C object tools/llvm-c-test/CMakeFiles/llvm-c-test.dir/object.c.obj
[2630/3025] Building C object tools/llvm-c-test/CMakeFiles/llvm-c-test.dir/helpers.c.obj
[2631/3025] Linking CXX executable bin\llvm-bcanalyzer.exe
[2631/3025] Linking CXX executable bin\llvm-bcanalyzer.exe
[2632/3025] Linking CXX executable bin\llvm-profdata.exe
[2633/3025] Linking CXX executable bin\llvm-as.exe
[2634/3025] Linking CXX static library lib\libLLVMPasses.a
ninja: build stopped: subcommand failed.
command did not execute successfully, got: exit code: 1


build script failed, must exit now', C:\Users\runneradmin\.cargo\registry\src\index.crates.io-6f17d22bba15001f\cmake-0.1.48\src\lib.rs:975:5
 finished in 229.322 seconds
Build completed successfully in 0:05:05
Build completed successfully in 0:05:05
make: *** [Makefile:80: ci-mingw-subset-2] Error 1

[rust-timer]

Finished benchmarking commit (044a28a): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.7%	[-3.2%, -2.1%]	4
All ❌✅ (primary)	-	-	0