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

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zackmdavis commented Mar 11, 2018

r? @nikomatsakis

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nikomatsakis commented Mar 12, 2018

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bors commented Mar 15, 2018

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

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nikomatsakis commented Apr 23, 2018

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

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zackmdavis commented Apr 24, 2018

Wednesday

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zackmdavis commented Apr 26, 2018

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

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zackmdavis commented Apr 26, 2018

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

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rust-highfive commented Apr 26, 2018

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)

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rust-highfive commented Apr 26, 2018

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

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estebank commented Apr 27, 2018

(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.

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bors commented Apr 27, 2018

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

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rust-highfive commented Apr 28, 2018

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)

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rust-highfive commented Apr 29, 2018

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)

zackmdavis added some commits Mar 10, 2018

in which the fn-must-use codepath is prevented from panicking on closure
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 (#15701) story being amicable).
stabilize `#[must_use]` for functions and must-use operators
This is in the matter of RFC 1940 and tracking issue #43302.
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zackmdavis commented Apr 29, 2018

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nikomatsakis commented Apr 30, 2018

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

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nikomatsakis commented Apr 30, 2018

@bors r+

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bors commented Apr 30, 2018

📌 Commit 3dbdccc has been approved by nikomatsakis

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GuillaumeGomez commented Apr 30, 2018

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

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bors commented Apr 30, 2018

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

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

Auto merge of #48925 - zackmdavis:fn_must_stabilize, r=nikomatsakis
stabilize `#[must_use]` for functions and must-use comparison operators (RFC 1940)

r? @nikomatsakis
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bors commented May 1, 2018

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

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

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@zackmdavis zackmdavis deleted the zackmdavis:fn_must_stabilize branch Jun 24, 2018

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