`#[must_use]` for associated functions is supposed to actually work by zackmdavis · Pull Request #55003 · rust-lang/rust

zackmdavis · 2018-10-12T06:20:57Z

In the comments of (closed, defunct) pull request #54884, @Centril noted that must-use annotations didn't work on an associated function (what other communities might call a "static method"). Subsequent logging revealed that in this case we have a Def::Method, whereas the lint pass was only matching on Def::Fn. (One could argue that those def-names are thereby misleading—must-use for self-ful methods have always worked—but documenting or reworking that can be left to another day.)

r? @varkor

rust-highfive · 2018-10-12T07:41:14Z

The job x86_64-gnu-llvm-5.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

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---
travis_time:start:test_codegen
Check compiletest suite=codegen mode=codegen (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:08:31] [01:08:31] running 111 tests
[01:08:34] i..ii...iii.......i...i.........i..iii...........i.....i.....ii...i.i.ii..............i...ii..ii.i.. 100/111
[01:08:34] ..iiii.....
[01:08:34] [01:08:34] finished in 3.398
[01:08:34] travis_fold:end:test_codegen
---
[01:17:43] [01:17:43] [01:17:43] running 403 tests
[01:17:58] .................................................................................................... 100/403
[01:18:08] .....................................................................i........................F..... 200/403
[01:18:19] ...............F.................................................................................... 300/403
[01:18:28] ..................F...................F............................................................. 400/403
[01:18:28] failures:
[01:18:28] [01:18:28] ---- rc.rs - rc::Rc<T>::clone (line 865) stdout ----
[01:18:28] ---- rc.rs - rc::Rc<T>::clone (line 865) stdout ----
[01:18:28] error: unused return value of `std::clone::Clone::clone` which must be used
[01:18:28] --> rc.rs:870:1
[01:18:28] |
[01:18:28] 8 | Rc::clone(&five);
[01:18:28] |
[01:18:28] note: lint level defined here
[01:18:28] --> rc.rs:864:9
[01:18:28] |
[01:18:28] |
[01:18:28] 2 | #![deny(warnings)]
[01:18:28] | ^^^^^^^^
[01:18:28] = note: #[deny(unused_must_use)] implied by #[deny(warnings)]
[01:18:28] = note: cloning is often expensive and is not expected to have side effects
[01:18:28] thread 'rc.rs - rc::Rc<T>::clone (line 865)' panicked at 'couldn't compile the test', librustdoc/test.rs:333:13
[01:18:28] note: Run with `RUST_BACKTRACE=1` for a backtrace.
[01:18:28] [01:18:28] ---- rc.rs - rc::Weak<T>::clone (line 1302) stdout ----
[01:18:28] ---- rc.rs - rc::Weak<T>::clone (line 1302) stdout ----
[01:18:28] error: unused return value of `std::clone::Clone::clone` which must be used
[01:18:28] --> rc.rs:1307:1
[01:18:28] |
[01:18:28] 8 | Weak::clone(&weak_five);
[01:18:28] |
[01:18:28] note: lint level defined here
[01:18:28] --> rc.rs:1301:9
[01:18:28] |
[01:18:28] |
[01:18:28] 2 | #![deny(warnings)]
[01:18:28] | ^^^^^^^^
[01:18:28] = note: #[deny(unused_must_use)] implied by #[deny(warnings)]
[01:18:28] = note: cloning is often expensive and is not expected to have side effects
[01:18:28] thread 'rc.rs - rc::Weak<T>::clone (line 1302)' panicked at 'couldn't compile the test', librustdoc/test.rs:333:13
[01:18:28] [01:18:28] ---- sync.rs - sync::Arc<T>::clone (line 711) stdout ----
[01:18:28] ---- sync.rs - sync::Arc<T>::clone (line 711) stdout ----
[01:18:28] error: unused return value of `std::clone::Clone::clone` which must be used
[01:18:28] --> sync.rs:716:1
[01:18:28] |
[01:18:28] 8 | Arc::clone(&five);
[01:18:28] |
[01:18:28] note: lint level defined here
[01:18:28] --> sync.rs:710:9
[01:18:28] |
[01:18:28] |
[01:18:28] 2 | #![deny(warnings)]
[01:18:28] | ^^^^^^^^
[01:18:28] = note: #[deny(unused_must_use)] implied by #[deny(warnings)]
[01:18:28] = note: cloning is often expensive and is not expected to have side effects
[01:18:28] thread 'sync.rs - sync::Arc<T>::clone (line 711)' panicked at 'couldn't compile the test', librustdoc/test.rs:333:13
[01:18:28] [01:18:28] ---- sync.rs - sync::Weak<T>::clone (line 1133) stdout ----
[01:18:28] ---- sync.rs - sync::Weak<T>::clone (line 1133) stdout ----
[01:18:28] error: unused return value of `std::clone::Clone::clone` which must be used
[01:18:28] --> sync.rs:1138:1
[01:18:28] |
[01:18:28] 8 | Weak::clone(&weak_five);
[01:18:28] |
[01:18:28] note: lint level defined here
[01:18:28] --> sync.rs:1132:9
[01:18:28] |
[01:18:28] |
[01:18:28] 2 | #![deny(warnings)]
[01:18:28] | ^^^^^^^^
[01:18:28] = note: #[deny(unused_must_use)] implied by #[deny(warnings)]
[01:18:28] = note: cloning is often expensive and is not expected to have side effects
[01:18:28] thread 'sync.rs - sync::Weak<T>::clone (line 1133)' panicked at 'couldn't compile the test', librustdoc/test.rs:333:13
[01:18:28] [01:18:28] [01:18:28] failures:
---
[01:18:28] [01:18:29] error: test failed, to rerun pass '--doc'
[01:18:29] [01:18:29] [01:18:29] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind jemalloc backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "alloc" "--" "--quiet"
[01:18:29] [01:18:29] [01:18:29] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:18:29] Build completed unsuccessfully in 0:28:15
[01:18:29] Build completed unsuccessfully in 0:28:15
[01:18:29] make: *** [check] Error 1
[01:18:29] Makefile:58: recipe for target 'check' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0314f2be
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

zackmdavis · 2018-10-13T03:51:38Z

(Travis pointed out that this affected some doctests in liballoc!)

rust-highfive · 2018-10-13T04:49:56Z

The job x86_64-gnu-llvm-5.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:51:02] .................................................................................................... 2200/4593
[00:51:07] ..............i..................................................................................... 2300/4593
[00:51:10] .................................................................................................... 2400/4593
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[00:58:05] ....................................................................
[00:58:05] failures:
[00:58:05] [00:58:05] ---- [run-pass] run-pass/resolve-pseudo-shadowing.rs stdout ----
[00:58:05] normalized stderr:
[00:58:05] warning: unused return value of `std::clone::Clone::clone` which must be used
[00:58:05] |
[00:58:05] |
[00:58:05] LL | <() as std::clone::Clone>::clone(&());
[00:58:05] |
[00:58:05] = note: #[warn(unused_must_use)] on by default
[00:58:05] = note: #[warn(unused_must_use)] on by default
[00:58:05] = note: cloning is often expensive and is not expected to have side effects
[00:58:05] [00:58:05] [00:58:05] [00:58:05] The actual stderr differed from the expected stderr.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

In the comments of (closed, defunct) pull request rust-lang#54884, Mazdak "Centril" Farrokhzad noted that must-use annotations didn't work on an associated function (what other communities might call a "static method"). Subsequent logging revealed that in this case we have a `Def::Method`, whereas the lint pass was only matching on `Def::Fn`. (One could argue that those def-names are thereby misleading—must-use for self-ful methods have always worked—but documenting or reworking that can be left to another day.)

varkor · 2018-10-13T10:00:01Z

One could argue that those def-names are thereby misleading—must-use for self-ful methods have always worked

That is quite confusing. It'd be good to address this later, I agree.

@bors r+

bors · 2018-10-13T10:00:03Z

📌 Commit ab91a6b has been approved by varkor

bors · 2018-10-13T17:03:54Z

⌛ Testing commit ab91a6b with merge 8f19cad...

@Centril

`#[must_use]` for associated functions is supposed to actually work In the comments of (closed, defunct) pull request #54884, @Centril [noted that](#54884 (comment)) must-use annotations didn't work on an associated function (what other communities might call a "static method"). Subsequent logging revealed that in this case we have a `Def::Method`, whereas the lint pass was only matching on `Def::Fn`. (One could argue that those def-names are thereby misleading—must-use for `self`-ful methods have always worked—but documenting or reworking that can be left to another day.) r? @varkor

bors · 2018-10-13T19:43:31Z

☀️ Test successful - status-appveyor, status-travis
Approved by: varkor
Pushing 8f19cad to master...

rust-highfive assigned varkor Oct 12, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Oct 12, 2018

zackmdavis mentioned this pull request Oct 12, 2018
in which we lint #[must_use] functions with discardable return type #54884
Closed

zackmdavis force-pushed the must_use_assoc_fn branch from b94903d to 718609bCompare October 13, 2018 03:50

zackmdavis force-pushed the must_use_assoc_fn branch from 718609b to ab91a6bCompare October 13, 2018 05:02

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 13, 2018

bors merged commit ab91a6b into rust-lang:masterOct 13, 2018

bors mentioned this pull request Oct 13, 2018
Unused result warning: "X which must" ↦ "X that must" #54917
Merged

zackmdavis deleted the must_use_assoc_fn branch October 14, 2018 19:00

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`#[must_use]` for associated functions is supposed to actually work - #55003

`#[must_use]` for associated functions is supposed to actually work#55003
bors merged 1 commit into
rust-lang:masterfrom
zackmdavis:must_use_assoc_fn

zackmdavis commented Oct 12, 2018

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zackmdavis commented Oct 12, 2018

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rust-highfive commented Oct 12, 2018

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zackmdavis commented Oct 13, 2018

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