Point at match discriminant on type error in match arm pattern

[estebank]

error[E0308]: mismatched types
 --> src/main.rs:5:9
  |
4 |    let temp: usize = match a + b {
  |                            ----- this expression has type `usize`
5 |         Ok(num) => num,
  |         ^^^^^^^ expected usize, found enum `std::result::Result`
  |
  = note: expected type `usize`
             found type `std::result::Result<_, _>`

Fix #57279.

[rust-highfive]

r? @michaelwoerister

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

[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:1ca07a40:start=1546737054986853010,finish=1546737055985198461,duration=998345451
$ 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
---

[00:03:57] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:03:57] tidy error: /checkout/src/librustc_typeck/check/_match.rs:733: line longer than 100 chars
[00:03:58] some tidy checks failed
[00:03:58] 
[00:03:58] 
[00:03:58] 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"
[00:03:58] 
[00:03:58] 
[00:03:58] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:03:58] Build completed unsuccessfully in 0:00:45
[00:03:58] Build completed unsuccessfully in 0:00:45
[00:03:58] Makefile:69: recipe for target 'tidy' failed
[00:03:58] make: *** [tidy] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0ee694d0
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Sun Jan  6 01:15:06 UTC 2019
---
travis_time:end:0270e3b4:start=1546737307038371472,finish=1546737307042821457,duration=4449985
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:03658b0c
$ 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:255700a1
travis_time:start:255700a1
$ 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:24752204
$ 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)

[michaelwoerister]

@varkor, would you be up for giving this a full review? Since my review backlog has grown a second page over the break, I'm glad about anything that I can hand off :)

[varkor]

r? @varkor

I'll take a proper look soon.

[michaelwoerister]

Thanks a lot, @varkor!

[varkor]

Looks good! r=me with the updated comment.

[varkor]

Looks good! r=me with the updated comment.

[estebank]

@bors r=varkor

[bors]

📌 Commit e70390a has been approved by varkor

[bors]

⌛️ Testing commit e70390a with merge 90db924...

[bors]

💔 Test failed - status-appveyor

[pietroalbini]

@bors retry
AppVeyor... what's wrong with you today?

[estebank]

rebased to get bors unstuck

@bors r=varkor

[bors]

📌 Commit 10fbdbf has been approved by varkor