stabilize `#[must_use]` for functions and must-use comparison operators (RFC 1940) #48925

zackmdavis · 2018-03-11T01:25:01Z

nikomatsakis · 2018-03-12T16:07:06Z

bors · 2018-03-15T18:56:22Z

☔ The latest upstream changes (presumably #47813) made this pull request unmergeable. Please resolve the merge conflicts.

nikomatsakis · 2018-04-23T19:47:50Z

No longer blocked. Needs rebase though, ping @zackmdavis =)

zackmdavis · 2018-04-24T00:42:50Z

Wednesday

zackmdavis · 2018-04-26T05:25:04Z

(rebased on unmerged PR #50149, which this would collide with conditional on #50149 being approved)

zackmdavis · 2018-04-26T05:26:28Z

(also left a comment on the tracking issue re whether to error on incorrect attribute placement)

rust-highfive · 2018-04-26T05:32:04Z

The job x86_64-gnu-llvm-3.9 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.

[00:05:11]    Compiling backtrace v0.3.6
[00:05:12]    Compiling syntax_pos v0.0.0 (file:///checkout/src/libsyntax_pos)
[00:05:12]    Compiling arena v0.0.0 (file:///checkout/src/libarena)
[00:05:15]    Compiling rustc_errors v0.0.0 (file:///checkout/src/librustc_errors)
[00:05:27] error[E0609]: no field `fn_must_use` on type `&feature_gate::Features`
[00:05:27]     --> libsyntax/feature_gate.rs:1342:39
[00:05:27]      |
[00:05:27] 1342 |               gate_feature!(cx.context, $feature, span, $explain, $level)
[00:05:27] ...
[00:05:27] ...
[00:05:27] 1549 | /                     gate_feature_post!(&self, fn_must_use, attr.span,
[00:05:27] 1550 | |                                        "`#[must_use]` on functions is experimental",
[00:05:27] 1551 | |                                        GateStrength::Soft);
[00:05:27]      | |___________________________________________________________- in this macro invocation
[00:05:27] 
[00:05:27] error[E0609]: no field `fn_must_use` on type `&feature_gate::Features`
[00:05:27]     --> libsyntax/feature_gate.rs:1342:39
[00:05:27] 1342

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)

rust-highfive · 2018-04-26T06:20:40Z

The job x86_64-gnu-llvm-3.9 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.

[00:21:21]    Compiling rustc_tsan v0.0.0 (file:///checkout/src/librustc_tsan)
[00:21:21]    Compiling rustc_lsan v0.0.0 (file:///checkout/src/librustc_lsan)
[00:21:22]    Compiling rustc_asan v0.0.0 (file:///checkout/src/librustc_asan)
[00:21:22]    Compiling rustc_msan v0.0.0 (file:///checkout/src/librustc_msan)
[00:22:00] error: this feature has been stable since 1.27.0. Attribute no longer needed
[00:22:00]    |
[00:22:00]    |
[00:22:00] 79 | #![feature(fn_must_use)]
[00:22:00]    |
[00:22:00]    |
[00:22:00]    = note: `-D stable-features` implied by `-D warnings`
[00:22:03] error: aborting due to previous error
[00:22:03] 
[00:22:03] error: Could not compile `core`.
[00:22:03] 
[00:22:03] 
[00:22:03] Caused by:
[00:22:03]   process didn't exit successfully: `/checkout/obj/build/bootstrap/debug/rustc --crate-name core libcore/lib.rs --color always --error-format json --crate-type lib --emit=dep-info,link -C opt-level=2 -C metadata=64878136ec7adadb -C extra-filename=-64878136ec7adadb --out-dir /checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps --target x86_64-unknown-linux-gnu -L dependency=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps -L dependency=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/release/deps` (exit code: 101)
[00:22:03] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "--release" "--locked" "--color" "always" "--features" "panic-unwind jemalloc backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "--message-format" "json"
[00:22:03] expected success, got: exit code: 101
[00:22:03] thread 'main' panicked at 'cargo must succeed', bootstrap/compile.rs:1091:9
[00:22:03] travis_fold:end:stage1-std

[00:22:03] travis_time:end:stage1-std:start=1524723582418145126,finish=1524723637263463266,duration=54845318140

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)

estebank · 2018-04-27T00:02:06Z

(rebased on unmerged PR #50149, which this would collide with conditional on #50149 being approved)

Just approved that PR so soon you should be able to rebase against master again.

bors · 2018-04-27T23:38:47Z

☔ The latest upstream changes (presumably #50290) made this pull request unmergeable. Please resolve the merge conflicts.

rust-highfive · 2018-04-28T23:44:05Z

The job x86_64-gnu-llvm-3.9 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.

[00:50:38] ............................................................................ii......................
[00:51:25] ........................................i....................................................i.ii...
[00:51:35] ........................test [run-pass] run-pass/saturating-float-casts.rs has been running for over 60 seconds
[00:52:06] ............................................................................
[00:52:26] .iiiiiii............................................................................................
[00:53:05] ....................................................................................................
[00:53:22] .........................................................................
[00:53:22] test result: ok. 2954 passed; 0 failed; 19 ignored; 0 measured; 0 filtered out
[00:53:22] 
---
[01:06:21] 
[01:06:21] To learn more, run the command again with --verbose.
[01:06:21] 
[01:06:21] 
[01:06:21] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-gnu" "--release" "--locked" "--color" "always" "--features" "panic-unwind jemalloc backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "alloc" "--" "--quiet"
[01:06:21] 
[01:06:21] 
[01:06:21] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:06:21] Build completed unsuccessfully in 0:26:23
[01:06:21] Build completed unsuccessfully in 0:26:23
[01:06:21] Makefile:58: recipe for target 'check' failed
[01:06:21] make: *** [check] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:11912cd8
$ 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)

rust-highfive · 2018-04-29T01:17:49Z

The job x86_64-gnu-llvm-3.9 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.

[00:56:38] ............................................................................ii......................
[00:57:33] ........................................i....................................................i.ii...
[00:57:35] ....test [run-pass] run-pass/saturating-float-casts.rs has been running for over 60 seconds
[00:58:16] ................................................................................................
[00:58:35] .iiiiiii............................................................................................
[00:59:17] ....................................................................................................
[00:59:36] .........................................................................
[00:59:36] test result: ok. 2954 passed; 0 failed; 19 ignored; 0 measured; 0 filtered out
[00:59:36] 
---
[01:22:43] travis_fold:start:test_stage1-std
travis_time:start:test_stage1-std
Testing std stage1 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:22:43]    Compiling std v0.0.0 (file:///checkout/src/libstd)
[01:23:13] error: unused return value of `core::clone::Clone::clone` which must be used: cloning is often expensive and is not expected to have side effects
[01:23:13]     |
[01:23:13]     |
[01:23:13] 529 |             tx1.clone();
[01:23:13]     |
[01:23:13]     |
[01:23:13]     = note: `-D unused-must-use` implied by `-D warnings`
[01:23:13] 
[01:23:13] error: unused return value of `core::clone::Clone::clone` which must be used: cloning is often expensive and is not expected to have side effects
[01:23:13]     |
[01:23:13]     |
[01:23:13] 551 |             tx1.clone();
[01:23:13] 
[01:23:13] 
-1wl4zjaz72e5d/s-f0jwusi57h-1w5ffv6-6gvofocobazn
112820 ./obj/build/x86_64-unknown-linux-gnu/test/mir-opt
111312 ./obj/build/x86_64-unknown-linux-gnu/stage0-tools/x86_64-unknown-linux-gnu
111308 ./obj/build/x86_64-unknown-linux-gnu/stage0-tools/x86_64-unknown-linux-gnu/release
107424 ./obj/build/x86_64-unknown-linux-gnu/stage0-tools/x86_64-unknown-linux-gnu/release/deps
107424 ./obj/build/x86_64-unknown-linux-gnu/stage0-tools/x86_64-unknown-linux-gnu/release/deps
102820 ./obj/build/x86_64-unknown-linux-gnu/stage0/lib/rustlib/x86_64-unknown-linux-gnu/codegen-backends
102808 ./obj/build/bootstrap/debug/incremental/bootstrap-2wettvttcntnm
102804 ./obj/build/bootstrap/debug/incremental/bootstrap-2wettvttcntnm/s-f0jy1sr9no-o2vsb4-v7hez0f2m5v0
90644 ./obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/incremental/core-31lccp6wy7orz
90644 ./obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/incremental/core-31lccp6wy7orz
90640 ./obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/incremental/core-31lccp6wy7orz/s-f0jxz7e8k9-1pa4mnj-t8uzx7gi46ua
89756 ./obj/build/x86_64-unknown-linux-gnu/stage1/lib
89704 ./src/llvm/test/CodeGen
86660 ./obj/build/x86_64-unknown-linux-gnu/doc/core
84436 ./obj/build/x86_64-unknown-linux-gnu/stage1-rustc/x86_64-unknown-linux-gnu/release/deps

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)

The must-use lint needs the DefId of called functions and method receivers in order to look for a `#[must_use]` attribute, but this would ICE (!) if a called function was actually a closure (with a non-unit return value). Instead, let's be specific that we want a `Def::Fn`, rather than blithely assuming that we can get the DefId of a qpath. Supporting must-use closures doesn't seem like a priority, but could conceivably be added in the future if desired (conditional on the statement and expression attributes (rust-lang#15701) story being amicable).

This is in the matter of RFC 1940 and tracking issue rust-lang#43302.

zackmdavis · 2018-04-29T05:10:34Z

@nikomatsakis ready

nikomatsakis · 2018-04-30T17:30:41Z

cc @rust-lang/docs -- this PR contains changed that will need to be documented in stable docs.

nikomatsakis · 2018-04-30T17:30:44Z

@bors r+

bors · 2018-04-30T17:30:45Z

📌 Commit 3dbdccc has been approved by nikomatsakis

GuillaumeGomez · 2018-04-30T20:33:49Z

@nikomatsakis: Why not adding it in this PR directly?

bors · 2018-04-30T22:02:40Z

⌛ Testing commit 3dbdccc with merge 357bf00...

@nikomatsakis

stabilize `#[must_use]` for functions and must-use comparison operators (RFC 1940) r? @nikomatsakis

bors · 2018-05-01T00:08:49Z

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 357bf00 to master...

rust-highfive assigned nikomatsakis Mar 11, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 11, 2018

This was referenced Mar 11, 2018

discussion/tracking issue for #[must_use] functions in the standard library #48926

Closed

Tracking issue for RFC 1940: allow #[must_use] on functions #43302

Closed

nikomatsakis added S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 12, 2018

pietroalbini added S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. and removed S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. labels Mar 26, 2018

shepmaster added S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. and removed S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. labels Apr 7, 2018

zackmdavis mentioned this pull request Apr 22, 2018

Added warning for unused arithmetic expressions #50149

Merged

nikomatsakis added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. labels Apr 23, 2018

nikomatsakis added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 23, 2018

zackmdavis force-pushed the fn_must_stabilize branch from f920bc2 to 442c708 Compare April 26, 2018 05:23

zackmdavis force-pushed the fn_must_stabilize branch from 442c708 to d8cbed9 Compare April 26, 2018 05:56

zackmdavis force-pushed the fn_must_stabilize branch from d8cbed9 to 9d5e08f Compare April 28, 2018 22:36

zackmdavis force-pushed the fn_must_stabilize branch from 9d5e08f to c26ff28 Compare April 28, 2018 23:53

zackmdavis force-pushed the fn_must_stabilize branch from c26ff28 to 4b9b957 Compare April 29, 2018 01:38

zackmdavis added 2 commits April 28, 2018 20:32

stabilize #[must_use] for functions and must-use operators

3dbdccc

This is in the matter of RFC 1940 and tracking issue rust-lang#43302.

zackmdavis force-pushed the fn_must_stabilize branch from 4b9b957 to 3dbdccc Compare April 29, 2018 03:33

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 30, 2018

nikomatsakis added the relnotes Marks issues that should be documented in the release notes of the next release. label Apr 30, 2018

bors added a commit that referenced this pull request Apr 30, 2018

Auto merge of #48925 - zackmdavis:fn_must_stabilize, r=nikomatsakis

357bf00

stabilize `#[must_use]` for functions and must-use comparison operators (RFC 1940) r? @nikomatsakis

bors merged commit 3dbdccc into rust-lang:master May 1, 2018

bors mentioned this pull request May 1, 2018

Remove unstable macro_reexport #49982

Merged

zackmdavis mentioned this pull request May 2, 2018

Document RFC 1940 (must_use on fns) rust-lang/reference#247

Merged

zackmdavis deleted the fn_must_stabilize branch June 24, 2018 00:17

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stabilize `#[must_use]` for functions and must-use comparison operators (RFC 1940) #48925

stabilize `#[must_use]` for functions and must-use comparison operators (RFC 1940) #48925

zackmdavis commented Mar 11, 2018

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bors commented May 1, 2018

stabilize #[must_use] for functions and must-use comparison operators (RFC 1940) #48925

stabilize #[must_use] for functions and must-use comparison operators (RFC 1940) #48925

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zackmdavis commented Mar 11, 2018

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stabilize `#[must_use]` for functions and must-use comparison operators (RFC 1940) #48925

stabilize `#[must_use]` for functions and must-use comparison operators (RFC 1940) #48925