error: remove StringError from Debug output

[seanmonstar]

Seeing StringError("something something") in debug output can cause
someone to think there was an error dealing with Strings, not that the
error type is just a string. So, remove that noise.

For example:

io error: Custom { kind: InvalidData, error: StringError("corrupt data") }

With this change:

io error: Custom { kind: InvalidData, error: "corrupt data" }

[rust-highfive]

r? @aidanhs

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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:015255c9:start=1558051979768053862,finish=1558051980565078828,duration=797024966
$ 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
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
$ export AWS_ACCESS_KEY_ID=AKIA46X5W6CZEJZ6XT55
---
[00:04:56] tidy error: /checkout/src/libstd/error.rs:314: trailing whitespace
[00:05:01] some tidy checks failed
[00:05:01] 
[00:05:01] 
[00:05:01] 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"
[00:05:01] 
[00:05:01] 
[00:05:01] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:05:01] Build completed unsuccessfully in 0:01:17
[00:05:01] Build completed unsuccessfully in 0:01:17
[00:05:01] make: *** [tidy] Error 1
[00:05:01] Makefile:67: recipe for target 'tidy' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:11f5dd36
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Fri May 17 00:18:13 UTC 2019
---
travis_time:end:068d263d:start=1558052294108971769,finish=1558052294114038516,duration=5066747
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:20543706
$ 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:12c2c73a
travis_time:start:12c2c73a
$ 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:315e9a21
$ 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)

[seanmonstar]

Ping?

[tesuji]

r? @Centril

[Centril]

r? @sfackler

[sfackler]

@bors r+ rollup

[bors]

📌 Commit d2d89b1 has been approved by sfackler

[LukasKalbertodt]

I know this PR was already merged, but while we're at it, can we just Display::fmt(&self.0, f) instead so that the string does not get escaped? The string in a StringError is made for humans to read, so I'd say escaping is useless in that case. Any counter arguments? If not, I'd open a PR.

[seanmonstar]

I'd typically expect the Debug format to escape strings. I wouldn't want newlines or whatever to be rendered, for instance.

[LukasKalbertodt]

@seanmonstar I agree in the general case. But in this case we are talking about an error description and not any String debug output. I can still understand your reasoning, but I think in this case escaping isn't doing any good. Suppose the string error contains the output of a GLSL compiler or something: in that case, I want the newlines.

[seanmonstar]

Couldn't formatting the error with Display get you the output you want?

[LukasKalbertodt]

True, but in many real life situations, errors are just formatted as Debug sadly :/