Fix ICE in rustdoc

[jseyfried]

Fixes#38237.
r? @nrc

[sanxiyn]

You shouldn't write in the source tree. (Source tree is mounted read-only on Travis to enforce this.) See #37176.

[nrc]

@bors: r+

[bors]

📌 Commit 1187e21 has been approved by nrc

[Arnavion]

I confirmed this fixes both the minimal repro as well as my original code. Thanks!

[bors]

⌛ Testing commit 1187e21 with merge d35f39b...

[bors]

💔 Test failed - status-travis

[alexcrichton]

@bors: retry

• Spurious segfault in tests for musl #38618

[bors]

⌛ Testing commit 1187e21 with merge 9351c2c...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: nrc
Pushing 9351c2c to master...

[nikomatsakis]

Marking as beta-accepted. Small patch, regression. cc @rust-lang/compiler

[nikomatsakis]

Wait, was this a regression @jseyfried ?

[jseyfried]

@nikomatsakis It was only a regression with #![feature(proc_macros)]. I still think it would be a good idea to backport though since it's such a small change.

[eddyb]

That feature is getting stabilized though.

[jseyfried]

@eddyb Right, but if we didn't backport it wouldn't technically be a regression from stable to stable.

[nikomatsakis]

OK, since we are stabilizing, let's backport. Marking as beta-accepted. cc @rust-lang/compiler

[infinity0]

This test is failing on 1.21.0 on Debian on amd64 and ppc64el:

warning: struct is never used: `S`
--> foo.rs:19:1
|
19 | struct S;
| ^^^^^^^^^
|
= note: #[warn(dead_code)] on by default
/<<BUILDDIR>>/rustc-1.21.0+dfsg1/build/powerpc64le-unknown-linux-gnu/stage2/bin/rustdoc: error while loading shared libraries: librustc_driver-be990221f14aebfb.so: cannot open shared object file: No such file or directory
make[2]: *** [all] Error 127

Does that struct S need to be a pub struct S?

[eddyb]

@infinity0 That's just the warning, the failure looks like broken dynamic linking or something.