Stabilize TryFrom and TryInto with a convert::Infallible empty enum #58302

SimonSapin · 2019-02-08T14:08:30Z

This is the plan proposed in #33417 (comment)

rust-highfive · 2019-02-08T14:08:33Z

r? @rkruppe

(rust_highfive has picked a reviewer for you, use r? to override)

SimonSapin · 2019-02-08T14:08:40Z

@rfcbot fcp merge

rfcbot · 2019-02-08T14:08:40Z

Team member @SimonSapin has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and none object), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

rust-highfive · 2019-02-08T15:12:15Z

The job x86_64-gnu-llvm-6.0 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.

travis_time:end:04d689f0:start=1549634997151285181,finish=1549635146244413755,duration=149093128574
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---
[00:58:49]     Checking compiler_builtins v0.1.5
[00:58:50]  Documenting alloc v0.0.0 (/checkout/src/liballoc)
[00:58:55]     Finished release [optimized] target(s) in 35.92s
[00:58:56]  Documenting core v0.0.0 (/checkout/src/libcore)
[00:59:12] warning: `[never]` cannot be resolved, ignoring it...
[00:59:12]     |
[00:59:12]     |
[00:59:12] 529 | /// This enum has the same role as [the `!` “never” type][never],
[00:59:12]     |
[00:59:12] note: lint level defined here
[00:59:12]    --> src/libcore/lib.rs:63:9
[00:59:12]     |
[00:59:12]     |
[00:59:12] 63  | #![warn(intra_doc_link_resolution_failure)]
[00:59:12]     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[00:59:12]     = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:59:12] 
[00:59:12] warning: `[never]` cannot be resolved, ignoring it...
[00:59:12]     |
[00:59:12]     |
[00:59:12] 529 | /// This enum has the same role as [the `!` “never” type][never],
[00:59:12]     |
[00:59:12]     = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:59:12] 
[00:59:18]     Finished release [optimized] target(s) in 23.19s
---
[00:59:24]     Checking rustc_tsan v0.0.0 (/checkout/src/librustc_tsan)
[00:59:24]     Checking rustc_msan v0.0.0 (/checkout/src/librustc_msan)
[00:59:24]     Checking rustc_asan v0.0.0 (/checkout/src/librustc_asan)
[00:59:24]  Documenting std v0.0.0 (/checkout/src/libstd)
[00:59:31] error: `[never]` cannot be resolved, ignoring it...
[00:59:31]     |
[00:59:31]     |
[00:59:31] 529 | /// This enum has the same role as [the `!` “never” type][never],
[00:59:31]     |
[00:59:31] note: lint level defined here
[00:59:31]    --> src/libstd/lib.rs:209:9
[00:59:31]     |
[00:59:31]     |
[00:59:31] 209 | #![deny(intra_doc_link_resolution_failure)]
[00:59:31]     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[00:59:31]     = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:59:31] 
[00:59:31] error: `[never]` cannot be resolved, ignoring it...
[00:59:31]     |
[00:59:31]     |
[00:59:31] 529 | /// This enum has the same role as [the `!` “never” type][never],
[00:59:31]     |
[00:59:31]     = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`
[00:59:31] 
[00:59:31] error: Could not document `std`.
[00:59:31] error: Could not document `std`.
[00:59:31] 
[00:59:31] Caused by:
[00:59:31]   process didn't exit successfully: `/checkout/obj/build/bootstrap/debug/rustdoc --crate-name std src/libstd/lib.rs --color always --target x86_64-unknown-linux-gnu -o /checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/doc --cfg 'feature="backtrace"' --cfg 'feature="backtrace-sys"' --cfg 'feature="compiler_builtins"' --cfg 'feature="compiler_builtins_c"' --cfg 'feature="default"' --cfg 'feature="panic-unwind"' --cfg 'feature="panic_unwind"' --markdown-css rust.css --markdown-no-toc --index-page /checkout/src/doc/index.md -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 --extern alloc=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/liballoc-9e6c0311b71511c6.rmeta --extern backtrace_sys=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/libbacktrace_sys-f13b165ed9b4dd57.rmeta --extern compiler_builtins=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/libcompiler_builtins-d54fe968dea87029.rmeta --extern core=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/libcore-84e5b9599b1b7754.rmeta --extern libc=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/liblibc-a69fda92b07aedd5.rmeta --extern panic_abort=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/libpanic_abort-349a3e5cce9f18ee.rmeta --extern panic_unwind=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/libpanic_unwind-d7c48504ff1056b6.rmeta --extern rustc_demangle=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/librustc_demangle-20814bca47e9a554.rmeta --extern rustc_asan=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/librustc_asan-8bc4c4bf1d4ec8f0.rmeta --extern rustc_lsan=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/librustc_lsan-0814373332ff833c.rmeta --extern rustc_msan=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/librustc_msan-655667bc8a1522d0.rmeta --extern rustc_tsan=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/librustc_tsan-5756fbda854daecf.rmeta --extern unwind=/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/release/deps/libunwind-5e31c590860d0940.rmeta` (exit code: 1)
[00:59:31] 
[00:59:31] 
[00:59:31] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "rustdoc" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-Z" "unstable-options" "-p" "std" "--" "--markdown-css" "rust.css" "--markdown-no-toc" "--index-page" "/checkout/src/doc/index.md"
[00:59:31] 
[00:59:31] 
[00:59:31] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap doc
[00:59:31] Build completed unsuccessfully in 0:06:12
[00:59:31] Build completed unsuccessfully in 0:06:12
[00:59:31] Makefile:18: recipe for target 'all' failed
[00:59:31] make: *** [all] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0e0d8a6d
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Fri Feb  8 15:12:07 UTC 2019
---
travis_time:end:0b378bfe:start=1549638728629181498,finish=1549638728633904520,duration=4723022
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:0103429f
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:0a0f6eff
travis_time:start:0a0f6eff
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:0503f1e2
$ dmesg | grep -i kill

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)

SimonSapin · 2019-02-08T15:23:30Z

src/libcore/convert.rs

+/// With `Infallible` being an enum, this code is valid.
+/// However when `Infallible` becomes an alias for the never type,
+/// the two `impl`s will start to overlap
+/// and therefore will be disallowed by the language’s trait coherence rules.


I think we want to add something here that says “so, uh, don’t do this?”. Wording suggestions welcome.

Is using one over the other preferable? Either way, maybe the answer to that should be in the docs.

alexcrichton

r=me on the code changes, thanks @SimonSapin!

alexcrichton · 2019-02-11T12:24:26Z

src/libcore/convert.rs

+    }
+}
+
+use fmt;


Could this be moved up to the top of the file?

alexcrichton · 2019-02-11T12:24:59Z

src/libcore/convert.rs

+}
+
+#[stable(feature = "convert_infallible", since = "1.34.0")]
+impl Eq for Infallible {}


With PartialEq and Eq perhaps the Ord-style traits could be included as well?

scottmcm · 2019-02-11T21:50:50Z

🎉 Huzzah! 🎉

Hopefully it sticks this time.

(Aside: #33417 (comment))

rfcbot · 2019-02-12T03:20:16Z

🔔 This is now entering its final comment period, as per the review above. 🔔

bors · 2019-02-12T08:32:16Z

☔ The latest upstream changes (presumably #58389) made this pull request unmergeable. Please resolve the merge conflicts.

hellow554 · 2019-02-13T13:24:26Z

src/libcore/convert.rs

+///
+/// # Future compatibility
+///
+/// This enum has the same role as [the `!` “never” type][never],


Maybe using regular quotes instead? "never"

hellow554 · 2019-02-13T13:24:50Z

src/libcore/convert.rs

+/// pub type Infallible = !;
+/// ```
+///
+/// … and eventually deprecate `Infallible`.


Maybe using three plain dots

hellow554 · 2019-02-13T13:27:56Z

src/libcore/convert.rs

+///
+///
+/// However there is one case where `!` syntax can be used
+/// before `!` is stabilized as a full-fleged type: in the position of a function’s return type.


hellow554 · 2019-02-13T13:28:08Z

src/libcore/convert.rs

+/// With `Infallible` being an enum, this code is valid.
+/// However when `Infallible` becomes an alias for the never type,
+/// the two `impl`s will start to overlap
+/// and therefore will be disallowed by the language’s trait coherence rules.


SimonSapin · 2019-02-13T13:48:47Z

@rust-lang/docs, any opinion on the use of non-ASCII v.s. ASCII punctuation in docs? I use the former out of habit.

GuillaumeGomez · 2019-02-13T14:23:15Z

We use it everywhere else in the doc so please use the ascii version of it. :)

frewsxcv · 2019-02-13T15:15:09Z

To my knowledge, the docs team has no agreed upon preference for smart quotes or ASCII quotes, so either is fine! I personally use smart quotes.

Nemo157 · 2019-02-13T16:39:18Z

src/libcore/convert.rs

+///
+///
+/// However there is one case where `!` syntax can be used
+/// before `!` is stabilized as a full-fleged type: in the position of a function’s return type.


Suggested change

/// before `!` is stabilized as a full-fleged type: in the position of a function’s return type.

/// before `!` is stabilized as a full-fledged type: in the position of a function’s return type.

"full-fledged" still looks wrong to me as a NZer, but Merriam-Webster seems to imply that "fully-fledged" is only a British thing.

jethrogb · 2019-02-13T16:54:54Z

It seems to me stabilizing the never type is close (#57012/#58184). Is it really necessary to do this now or can we wait just a little bit longer?

Centril · 2019-02-25T15:29:15Z

Since this is a stabilization PR, we want to get it in before master=>beta promotion, so: @bors p=50

bors · 2019-02-25T17:45:10Z

⌛ Testing commit cf26754 with merge 2e616be96c6c14265a4f55ca59f90f143e8b36a1...

bors · 2019-02-25T18:18:11Z

💔 Test failed - checks-travis

rust-highfive · 2019-02-25T18:18:13Z

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.

Attempting to download s3://rust-lang-ci-sccache2/docker/1f08d22f2a5e39c33797b6e95be989c2f1c727b72a5f7eeb8d59fa21b0c4483b32db64e100e5a6edf7e52a2b4841266c0b6e400d243c0f6e6db4570618ce4831
[00:00:14] Attempting with retry: curl -y 30 -Y 10 --connect-timeout 30 -f -L -C - -o /tmp/rustci_docker_cache https://s3-us-west-1.amazonaws.com/rust-lang-ci-sccache2/docker/1f08d22f2a5e39c33797b6e95be989c2f1c727b72a5f7eeb8d59fa21b0c4483b32db64e100e5a6edf7e52a2b4841266c0b6e400d243c0f6e6db4570618ce4831
[00:00:14]   % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
[00:00:14]                                  Dload  Upload   Total   Spent    Left  Speed
No output has been received in the last 30m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received
The build has been terminated

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SimonSapin · 2019-02-25T19:18:13Z

@bors retry

bors · 2019-02-25T20:24:17Z

⌛ Testing commit cf26754 with merge 00aae71...

Stabilize TryFrom and TryInto with a convert::Infallible empty enum This is the plan proposed in #33417 (comment)

bors · 2019-02-25T23:23:03Z

☀️ Test successful - checks-travis, status-appveyor
Approved by: alexcrichton
Pushing 00aae71 to master...

bors · 2019-02-25T23:23:13Z

☀️ Test successful - checks-travis, status-appveyor
Approved by: alexcrichton
Pushing 00aae71 to master...

jethrogb · 2019-04-26T19:49:17Z

We're missing impl From<Infallible> for TryFromSliceError, see #60318

SimonSapin added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Feb 8, 2019

rust-highfive assigned hanna-kruppe Feb 8, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Feb 8, 2019

rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Feb 8, 2019

SimonSapin commented Feb 8, 2019

View reviewed changes

SimonSapin force-pushed the tryfrom branch from 8caea7f to 1203b24 Compare February 9, 2019 13:18

alexcrichton reviewed Feb 11, 2019

View reviewed changes

Centril added the relnotes Marks issues that should be documented in the release notes of the next release. label Feb 11, 2019

rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Feb 12, 2019

SimonSapin force-pushed the tryfrom branch from 1203b24 to 8413a31 Compare February 12, 2019 08:54

hellow554 reviewed Feb 13, 2019

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glaebhoerl mentioned this pull request Feb 13, 2019

Tracking issue for TryFrom/TryInto traits #33417

Closed

3 tasks

Nemo157 reviewed Feb 13, 2019

View reviewed changes

Add a convert::Infallible empty enum, make string::ParseError an alias

85f13f0

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 Feb 25, 2019

bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Feb 25, 2019

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 Feb 25, 2019

bors added a commit that referenced this pull request Feb 25, 2019

Auto merge of #58302 - SimonSapin:tryfrom, r=alexcrichton

00aae71

Stabilize TryFrom and TryInto with a convert::Infallible empty enum This is the plan proposed in #33417 (comment)

bors mentioned this pull request Feb 25, 2019

Allow lang and lib features to share names #58741

Merged

bors added the merged-by-bors This PR was explicitly merged by bors. label Feb 25, 2019

bors merged commit cf26754 into rust-lang:master Feb 25, 2019

This was referenced Feb 25, 2019

libstd => 2018 #58208

Merged

libcore => 2018 #58702

Merged

SimonSapin deleted the tryfrom branch February 26, 2019 13:41

KeenS mentioned this pull request Mar 13, 2019

ungate try_from because it has been stabilized diesel-rs/diesel#2010

Merged

yoshuawuyts mentioned this pull request Mar 13, 2019

add TcpStream from std conversion withoutboats/romio#78

Merged

prasannavl mentioned this pull request Apr 2, 2019

add TryFrom impls for path, scheme, uri and authority hyperium/http#308

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Centril added this to the 1.34 milestone Apr 26, 2019

SimonSapin mentioned this pull request Nov 28, 2019

Regression in Error conversion from Infallible #66757

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LukasKalbertodt mentioned this pull request Jan 29, 2020

Change FromStr for String to use Infallible directly #67925

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faern mentioned this pull request Mar 25, 2021

Add impl Into<!> for Infallible #83493

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Stabilize TryFrom and TryInto with a convert::Infallible empty enum #58302

Stabilize TryFrom and TryInto with a convert::Infallible empty enum #58302

SimonSapin commented Feb 8, 2019

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SimonSapin commented Feb 8, 2019

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edited by sfackler

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jethrogb commented Apr 26, 2019

	/// before `!` is stabilized as a full-fleged type: in the position of a function’s return type.
	/// before `!` is stabilized as a full-fledged type: in the position of a function’s return type.

Stabilize TryFrom and TryInto with a convert::Infallible empty enum #58302

Stabilize TryFrom and TryInto with a convert::Infallible empty enum #58302

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