stabilize #[used] #51363

japaric · 2018-06-05T08:50:02Z

RFC for stabilization: rust-lang/rfcs#2386

Where should this be documented? Currently the documentation is in the unstable book

oli-obk · 2018-06-05T09:02:46Z

src/libsyntax/feature_gate.rs

@@ -609,6 +606,8 @@ declare_features! (
    (accepted, fn_must_use, "1.27.0", Some(43302), None),
    // Allows use of the :lifetime macro fragment specifier
    (accepted, macro_lifetime_matcher, "1.27.0", Some(34303), None),
+    // Used to preserve symbols (see llvm.used)
+    (accepted, used, "1.28.0", Some(40289), None),
 );

 // If you change this, please modify src/doc/unstable-book as well. You must


Do we even have an entry in the unstable-book? If yes, apply this comment, if no, we should probably document it together with stabilization.

Do we even have an entry in the unstable-book?

Yes.

If yes, apply this comment

I asked in the PR description where the documentation should be moved to as there are a few options (reference, book, RBE, etc.)

I would have assumed to add it to the book, because that would have been where I'd have searched for it.

@steveklabnik thinks otherwise (cf. #51366 (comment) and #51366 (comment)). I'll prep a PR to add documentation to the reference and the nomicon.

rust-highfive · 2018-06-05T09:05:01Z

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.

tidy check
[00:04:50] * 547 error codes
[00:04:50] * highest error code: E0911
[00:04:50] * 205 features
[00:04:50] tidy error: The Unstable Book has a 'language feature' section 'used' which doesn't correspond to an unstable language feature
[00:04:51] some tidy checks failed
[00:04:51] 
[00:04:51] 
[00:04:51] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:04:51] 
[00:04:51] 
[00:04:51] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:04:51] Build completed unsuccessfully in 0:01:51
[00:04:51] Build completed unsuccessfully in 0:01:51
[00:04:51] Makefile:79: recipe for target 'tidy' failed
[00:04:51] make: *** [tidy] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:26ed04ba
$ 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)

Centril · 2018-06-05T17:49:38Z

r? @oli-obk

bors · 2018-06-09T01:35:56Z

☔ The latest upstream changes (presumably #51448) made this pull request unmergeable. Please resolve the merge conflicts.

fitzgen · 2018-06-15T18:53:49Z

Can someone explain to me why this can only be applied to static items? It would be useful for exporting "unused" extern "C" fns from nested crates so that they appear in the final artifact (dylib/wasm/whatever).

japaric · 2018-06-20T01:37:35Z

Can someone explain to me why this can only be applied to static items?

A few reasons:

#[used] on functions is backward compatible to add / implement.
#[used] on functions needs a design (RFC) that defines where it is allowed: for instance,e is #[used] valid on generic functions? what would that even mean? how would that be implemented?
Keeping a unused function can be achieved using the current implementation of #[used] like this:

extern "C" fn keep_this() {}

#[used]
static KEEP: extern "C" fn() = keep_this;

japaric · 2018-06-20T15:03:53Z

Documentation PRs: rust-lang/reference#361 and rust-lang/nomicon#74

We had been using `#[no_mangle]` which is a workaround to ensure that the compiler doesn't drop important symbols. `#[used]` is designed explicitly for this purpose. rust-lang/rust#51363

pietroalbini · 2018-06-25T15:10:46Z

Now that the docs PRs are sent should we start the FCP process? cc @rust-lang/lang

eddyb · 2018-06-25T19:42:16Z

Wasn't the name quite controversial? Are we going with #[used] for sure?

Centril · 2018-06-25T19:46:31Z

@eddyb we accepted an RFC to stabilize with that name after a lot of bikeshed, so I'd say yes :)

eddyb · 2018-06-25T19:50:14Z

Ah, I see, rust-lang/rfcs#2386 (comment). That's sad but I won't block the stabilization (#40289).

kennytm · 2018-06-25T19:55:50Z

src/libsyntax/feature_gate.rs

@@ -609,6 +606,8 @@ declare_features! (
    (accepted, fn_must_use, "1.27.0", Some(43302), None),
    // Allows use of the :lifetime macro fragment specifier
    (accepted, macro_lifetime_matcher, "1.27.0", Some(34303), None),
+    // Used to preserve symbols (see llvm.used)
+    (accepted, used, "1.28.0", Some(40289), None),


This should be changed to 1.29.0 before merging.

Centril · 2018-06-25T20:03:05Z

@eddyb Hah :P You even ticked your own box on the RFC ;)

eddyb · 2018-06-27T09:42:18Z

@Centril I ticked my box during the discussion about the name, which I was hoping would result in a better alternative being chosen. Acceptance of the RFC, with #[used], was done afterwards.

We had been using `#[no_mangle]` which is a workaround to ensure that the compiler doesn't drop important symbols. `#[used]` is designed explicitly for this purpose. rust-lang/rust#51363

TimNN · 2018-07-03T17:39:45Z

Ping from triage, @oli-obk / @rust-lang/lang: IIUC, this PR is waiting for one of you to trigger an FCP.

cramertj · 2018-07-03T17:44:18Z

@TimNN #[used] has already been proposed for stabilization on the tracking issue. The FCP has not yet started-- still waiting for checkboxes.

TimNN · 2018-07-03T17:46:20Z

Ah, thank you @cramertj, I hadn't noticed that. Marking as blocked on #40289.

japaric · 2018-07-03T17:57:53Z

To clear the PR queue, I'm going to close this until the FCP period is over.

Centril · 2018-09-08T19:46:26Z

FCP period is now over.

@japaric can you resolve the conflicts / rebase? =P

closes rust-lang#40289

it'll be documented in the reference

japaric · 2018-09-09T13:58:08Z

@Centril I have rebased the PR. I have also pushed a commit that removes the chapter from the unstable book since there is a PR to document this in the reference (which I still need to update).

rust-highfive · 2018-09-09T15:54:58Z

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.

[00:46:30] ....................................................................................................
[00:46:32] ....................................................................................................
[00:46:35] ....................................................................................................
[00:46:37] ....................................................................................................
[00:46:39] .....................................................F..............................................
[00:46:43] .................F.................i................................................................
[00:46:46] ..i.................................................................................................
[00:46:52] .......................................................................................i............
[00:46:54] ....................................................................................................
[00:46:57] ....................................................................................................
[00:47:00] ....................................................................................................
---
[00:52:31] 
[00:52:31] ---- [ui] ui/feature-gates/feature-gate-linker-flavor.rs stdout ----
[00:52:31] diff of stderr:
[00:52:31] 
[00:52:31] - error[E0658]: the `#[used]` attribute is an experimental feature (see issue #40289)
[00:52:31] + error: attribute must be applied to a `static` variable
[00:52:31] 2   --> $DIR/feature-gate-linker-flavor.rs:16:1
[00:52:31] 3    |
[00:52:31] 4 LL | #[used]
[00:52:31] 5    | ^^^^^^^
[00:52:31] -    |
[00:52:31] -    = help: add #![feature(used)] to the crate attributes to enable
[00:52:31] 8 
---
[00:52:31] 12 
[00:52:31] 
[00:52:31] 
[00:52:31] The actual stderr differed from the expected stderr.
[00:52:31] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-linker-flavor/feature-gate-linker-flavor.stderr
[00:52:31] To update references, rerun the tests and pass the `--bless` flag
[00:52:31] To only update this specific test, also pass `--test-args feature-gates/feature-gate-linker-flavor.rs`
[00:52:31] error: 1 errors occurred comparing output.
[00:52:31] status: exit code: 1
[00:52:31] status: exit code: 1
[00:52:31] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/feature-gates/feature-gate-linker-flavor.rs" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-linker-flavor/a" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-linker-flavor/auxiliary" "-A" "unused"
[00:52:31] ------------------------------------------
[00:52:31] 
[00:52:31] ------------------------------------------
[00:52:31] stderr:
[00:52:31] stderr:
[00:52:31] ------------------------------------------
[00:52:31] {"message":"attribute must be applied to a `static` variable","code":null,"level":"error","spans":[{"file_name":"/checkout/src/test/ui/feature-gates/feature-gate-linker-flavor.rs","byte_start":702,"byte_end":709,"line_start":16,"line_end":16,"column_start":1,"column_end":8,"is_primary":true,"text":[{"text":"#[used]","highlight_start":1,"highlight_end":8}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"render

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)

kennytm · 2018-09-10T03:05:13Z

src/libsyntax/feature_gate.rs

@@ -674,6 +671,9 @@ declare_features! (
    // Allows all literals in attribute lists and values of key-value pairs.
    (accepted, attr_literals, "1.30.0", Some(34981), None),
    (accepted, panic_handler, "1.30.0", Some(44489), None),
+    // Used to preserve symbols (see llvm.used)
+    (accepted, used, "1.29.0", Some(40289), None),


Time flies, this should be 1.30.0 now (or 1.31.0 if it can't be merged this week).

cramertj · 2018-09-10T17:19:02Z

@bors r+

bors · 2018-09-10T17:19:03Z

📌 Commit d37658a has been approved by cramertj

bors · 2018-09-11T08:54:19Z

⌛ Testing commit d37658a with merge 7ee7207...

@Centril

stabilize #[used] closes #40289 RFC for stabilization: rust-lang/rfcs#2386 r? @Centril Where should this be documented? Currently the documentation is in the unstable book

bors · 2018-09-11T11:26:22Z

☀️ Test successful - status-appveyor, status-travis
Approved by: cramertj
Pushing 7ee7207 to master...

rust-highfive assigned Centril Jun 5, 2018

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 5, 2018

oli-obk reviewed Jun 5, 2018

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rust-highfive assigned oli-obk and unassigned Centril Jun 5, 2018

liigo mentioned this pull request Jun 6, 2018

Tracking issue for the #[used] attribute #40289

Closed

This was referenced Jun 20, 2018

document #[used] rust-lang/reference#361

Merged

document #[used] rust-lang/nomicon#74

Closed

pietroalbini added T-lang Relevant to the language team, which will review and decide on the PR/issue. relnotes Marks issues that should be documented in the release notes of the next release. labels Jun 25, 2018

bradjc mentioned this pull request Jun 25, 2018

Ensure symbols reach the linker with #[used] tock/tock#1026

Merged

2 tasks

kennytm reviewed Jun 25, 2018

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TimNN added the S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. label Jul 3, 2018

TimNN removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 3, 2018

japaric closed this Jul 3, 2018

Centril reopened this Sep 8, 2018

japaric added 2 commits September 9, 2018 15:43

stabilize #[used]

2fb5d5d

closes rust-lang#40289

remove #[used] from the unstable book

f4148a6

it'll be documented in the reference

japaric force-pushed the stable-used branch from d5a2b73 to f4148a6 Compare September 9, 2018 13:57

update ui tests

4429471

kennytm reviewed Sep 10, 2018

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bump version

d37658a

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-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. labels Sep 10, 2018

bors merged commit d37658a into rust-lang:master Sep 11, 2018

bors mentioned this pull request Sep 11, 2018

stabilize outlives requirements #53793

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stabilize #[used] #51363

stabilize #[used] #51363

japaric commented Jun 5, 2018

oli-obk Jun 5, 2018

japaric Jun 5, 2018

oli-obk Jun 5, 2018

japaric Jun 20, 2018

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Centril commented Jun 5, 2018

bors commented Jun 9, 2018

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japaric commented Jun 20, 2018

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pietroalbini commented Jun 25, 2018

eddyb commented Jun 25, 2018

Centril commented Jun 25, 2018

eddyb commented Jun 25, 2018

kennytm Jun 25, 2018

Centril commented Jun 25, 2018

eddyb commented Jun 27, 2018

TimNN commented Jul 3, 2018

cramertj commented Jul 3, 2018 •

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TimNN commented Jul 3, 2018

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kennytm Sep 10, 2018

cramertj commented Sep 10, 2018

bors commented Sep 10, 2018

bors commented Sep 11, 2018

bors commented Sep 11, 2018

stabilize #[used] #51363

stabilize #[used] #51363

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