Repository: rust
Issue: Doc tests fail on armv7 for error codes E0778 and E0779 (`instruction_set` attribute)
Labels: A-testsuite,O-Arm,C-bug

I maintain the `rust` package for the Mageia Linux distribution (RPM-based), syncing the .spec file with @cuviper's Fedora package.

Rust 1.50.0 doc tests are failing on Linux armv7 after the addition of the `instruction_set` attribution.
According to @cuviper the same tests also fail for Fedora on armv7.

I haven't tried newer Rust versions but the affected files haven't been changed on `master` since #76260 (https://github.com/rust-lang/rust/blob/master/compiler/rustc_error_codes/src/error_codes/E0778.md and https://github.com/rust-lang/rust/blob/master/compiler/rustc_error_codes/src/error_codes/E0779.md).

Log output:
```
test /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0765 (line 15354) ... ok
test /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0778 (line 15638) ... FAILED
test /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0778 (line 15647) ... FAILED
test /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0766 (line 15369) ... ok
test /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0779 (line 15680) ... FAILED
test /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0779 (line 15664) ... ok
<snip>
test /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0777 (line 15615) ... ok

failures:

---- /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0778 (line 15638) stdout ----
error[E0779]: target does not support `#[instruction_set]`
 --> /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md:15641:31
  |
5 | #[cfg_attr(target_arch="arm", instruction_set(arm::a32))]
  |                               ^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0779`.
Couldn't compile the test.
---- /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0778 (line 15647) stdout ----
error[E0779]: target does not support `#[instruction_set]`
 --> /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md:15650:31
  |
5 | #[cfg_attr(target_arch="arm", instruction_set(arm::t32))]
  |                               ^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0779`.
Couldn't compile the test.
---- /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0779 (line 15680) stdout ----
error[E0779]: target does not support `#[instruction_set]`
 --> /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md:15683:31
  |
4 | #[cfg_attr(target_arch="arm", instruction_set(arm::a32))] // ok!
  |                               ^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0779`.
Couldn't compile the test.

failures:
    /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0778 (line 15638)
    /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0778 (line 15647)
    /home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md - Rust_Compiler_Error_Index::E0779 (line 15680)

test result: FAILED. 957 passed; 3 failed; 19 ignored; 0 measured; 0 filtered out; finished in 29.15s



command did not execute successfully: "/home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/bootstrap/debug/rustdoc" "-Winvalid_codeblock_attributes" "-Dwarnings" "-Znormalize-docs" "--test" "/home/iurt/rpmbuild/BUILD/rustc-1.50.0-src/build/armv7-unknown-linux-gnueabihf/test/error-index.md" "--test-args" ""
expected success, got: exit code: 101
```

I don't have direct access to an armv7 machine to test further, this comes straight from Mageia's buildsystem after an armv7 build failure due to tests not passing.

Here's the full build log: [build.armv7hl.0.20210323072802.log](https://github.com/rust-lang/rust/files/6201051/build.armv7hl.0.20210323072802.log)