Add From<bool> for int types

[clarfonthey]

Fixes #46109.

[rust-highfive]

r? @TimNN

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[rust-highfive]

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.

[01:11:39]    Compiling core v0.0.0 (file:///checkout/src/libcore)
[01:11:53] error[E0282]: type annotations needed
[01:11:53]    --> libcore/../libcore/tests/result.rs:223:19
[01:11:53]     |
[01:11:53] 223 |         let val = Ok(1)?;
[01:11:53]     |                   ^^^^^^ cannot infer type for `_`
[01:11:54] error: aborting due to previous error
[01:11:54] 
[01:11:54] For more information about this error, try `rustc --explain E0282`.
[01:11:54] error: Could not compile `core`.
[01:11:54] error: Could not compile `core`.
[01:11:54] 
[01:11:54] To learn more, run the command again with --verbose.
[01:11:54] 
[01:11:54] 
[01:11:54] 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" "core" "--" "--quiet"
[01:11:54] 
[01:11:54] 
[01:11:54] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:11:54] Build completed unsuccessfully in 0:28:38
[01:11:54] Build completed unsuccessfully in 0:28:38
[01:11:54] Makefile:58: recipe for target 'check' failed
[01:11:54] make: *** [check] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0ebdfa38
$ 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)

[clarfonthey]

Actually, apparently this causes inference issues. That should probably be investigated before this is merged.

[sugar700]

fn try_result_ok() -> Result<u8, u8> {
    let val = Ok(1)?;
    Ok(val)
}

Ok(x)? for Result<_, u8> (as well as variations like return Err(u8::from(unimplemented!()));) sound like an edge case for me - I don't think realistically anyone would write code like this. This can be written as x, and I think this inference failure is not a practical issue. The test here could be changed to use a type other than u8, for example fn try_result_ok() -> Result<u8, bool>.

Additionally, according to https://github.com/rust-lang/rfcs/blob/master/text/1105-api-evolution.md, this would be a minor change.

[TimNN]

cc @rust-lang/libs: This has the potential to be inference-breaking. What do you think? Does this need a crater run?

[therealprof]

@SimonSapin The motivation for this is automatically generated code by svd2rust. Ideally we would like to use From for all types but that doesn't work for bool so we have to use as instead which generates a lot of noise. There alternative would be to special case per type which is also not desirable.

[clarfonthey]

Also, the main purpose of the lint is that in general, From should be used when the conversion is lossless, as as allows lossy conversions. This helps in macros and other places to ensure that only lossless conversions occur.

[alexcrichton]

Yeah I think it wouldn't hurt to get a crater run for this.

cc @rust-lang/infra, mind scheduling a crater run here?

[kennytm]

@bors try

[bors]

⌛ Trying commit a882197034b9b3eafb5e35c3f010d21fca0e0df4 with merge 4b647638d12b7679c1eee120c4c064bc749eb782...

[bors]

☀️ Test successful - status-travis
State: approved= try=True

[Mark-Simulacrum]

Check-only crater run started.

[emilyalbini]

Hi @alexcrichton (crater requester), @TimNN (PR reviewer)! Crater results are at: http://cargobomb-reports.s3.amazonaws.com/pr-50554/index.html. 'Blacklisted' crates (spurious failures etc) can be found here. If you see any spurious failures not on the list, please make a PR against that file.

(interested observers: Crater is a tool for testing the impact of changes on the crates.io ecosystem. You can find out more at the repo if you're curious)

[emilyalbini]

And both of the regressions are spurious \o/.

[TimNN]

This looks good to go, @clarcharr can you fix the travis failure?

Also cc @rust-lang/libs, I will approve this unless you have any objections. I overlooked that since the impls are insta-stable this should go through an FCP.

[scottmcm]

Since adding impls is a stabilization, doesn't this need an FCP?

[clarfonthey]

@TimNN Will do! Although I agree with @scottmcm that this needs an FCP.

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

[clarfonthey]

I rebased but there weren't actually any merge conflicts.

[TimNN]

@bors r+

[bors]

📌 Commit b1797d5 has been approved by TimNN

[bors]

⌛ Testing commit b1797d5 with merge 4a9bf7c...

[bors]

💔 Test failed - status-travis

[rust-highfive]

The job dist-x86_64-netbsd 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.

  0     0    0     0    0     0      0      0 --:--:--  0:00:15 --:--:--     0
  0     0    0     0    0     0      0      0 --:--:--  0:00:16 --:--:--     0
  0     0    0     0    0     0      0      0 --:--:--  0:00:17 --:--:--     0
  0     0    0     0    0     0      0      0 --:--:--  0:00:18 --:--:--     0
  0     0    0     0    0     0      0      0 --:--:--  0:00:19 --:--:--     0curl: (6) Could not resolve host: s3-us-west-1.amazonaws.com
[01:13:28] thread 'main' panicked at 'failed to download openssl source: exit code: 6', bootstrap/native.rs:575:17
[01:13:28] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap dist --host x86_64-unknown-netbsd --target x86_64-unknown-netbsd
[01:13:28] Build completed unsuccessfully in 1:09:53
travis_time:end:08518c12:start=1527916642471126256,finish=1527921051331467157,duration=4408860340901

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]

The job dist-x86_64-netbsd 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.

  0     0    0     0    0     0      0      0 --:--:--  0:00:15 --:--:--     0
  0     0    0     0    0     0      0      0 --:--:--  0:00:16 --:--:--     0
  0     0    0     0    0     0      0      0 --:--:--  0:00:17 --:--:--     0
  0     0    0     0    0     0      0      0 --:--:--  0:00:18 --:--:--     0
  0     0    0     0    0     0      0      0 --:--:--  0:00:19 --:--:--     0curl: (6) Could not resolve host: s3-us-west-1.amazonaws.com
[01:13:28] thread 'main' panicked at 'failed to download openssl source: exit code: 6', bootstrap/native.rs:575:17
[01:13:28] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap dist --host x86_64-unknown-netbsd --target x86_64-unknown-netbsd
[01:13:28] Build completed unsuccessfully in 1:09:53
travis_time:end:08518c12:start=1527916642471126256,finish=1527921051331467157,duration=4408860340901

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]

@bors retry #40474

[bors]

⌛ Testing commit b1797d5 with merge 2954cb5...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: TimNN
Pushing 2954cb5 to master...