Change char::eq_ignore_ascii_case to take a Borrow<char> instead of &char

[czipperz]

Resolves #57227

[rust-highfive]

r? @shepmaster

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[rust-highfive]

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:1a5252d8:start=1546227364068257708,finish=1546227365339012482,duration=1270754774
$ 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
---
[00:03:27] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "--message-format" "json"
[00:03:27] expected success, got: exit code: 101
[00:03:27] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap build
[00:03:27] Build completed unsuccessfully in 0:00:10
[00:03:27] Makefile:18: recipe for target 'all' failed
[00:03:27] make: *** [all] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:01ce32dc
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Mon Dec 31 03:39:41 UTC 2018

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]

Personally, I'd rather see these deprecated entirely for char. While they avoid allocation for str, x.eq_ignore_ascii_case(y) for char is not any easier than x.to_ascii_lowercase() == y.

[czipperz]

@clarcharr x.eq_ignore_ascii_case(&y) is synonymous with x.to_ascii_lowercase() == y.to_ascii_lowercase(), which is much more verbose.

[clarfonthey]

...right, I don't know how I messed that up.

I'm still not super fond of this method and wonder if there's a more ergonomic way to do this.

[shepmaster]

I'm unclear on how we deal with this backwards compatibility aspect. For example, this shows a form of code that would fail with the proposed changes:

fn before(_: &char, _: &char) -> bool {
    false
}

fn after(_: &char, _: impl std::borrow::Borrow<char>) -> bool {
    false
}

fn example(_: fn(&char, &char) -> bool) {}

fn main() {
    example(before);
    example(after);
}

r? @BurntSushi

[czipperz]

Nice catch @shepmaster . I was hoping Rust would automatically deduce the types. I think for this reason I don't think this PR should be merged. I'm going to work on making tests for these things. I need to get a real development environment set up first.

[TimNN]

Ping from triage @czipperz: What is the status of this PR? Should it be closed for now? Or do you think you'll be able to work on fixing the issue?

[czipperz]

Yeah shoot I forget to close this @TimNN