Spurious failure in RLS tests

[alexcrichton]

First seen on #43361 as https://ci.appveyor.com/project/rust-lang/rust/build/1.0.4048/job/8raxjkn064e3yimc, looks like:

running 14 tests
test server::test::server_message_get_method_name ... ok
test build::cargo::test::test_dedup_flags ... ok
test server::test::server_message_to_str ... ok
{"message":"cannot find struct, variant or union type `LibCfgTestStruct` in module `bin_lib_no_cfg_test`","code":{"code":"E0422","explanation":"\nYou are trying to use an identifier that is either undefined or not a struct.\nErroneous code example:\n\n```compile_fail,E0422\nfn main () {\n    let x = Foo { x: 1, y: 2 };\n}\n```\n\nIn this case, `Foo` is undefined, so it inherently isn't anything, and\ndefinitely not a struct.\n\n```compile_fail\nfn main () {\n    let foo = 1;\n    let x = foo { x: 1, y: 2 };\n}\n```\n\nIn this case, `foo` is defined, but is not a struct, so Rust can't use it as\none.\n"},"level":"error","spans":[{"file_name":"test_data\\bin_lib_no_cfg_test\\src\\main.rs","byte_start":130,"byte_end":146,"line_start":5,"line_end":5,"column_start":37,"column_end":53,"is_primary":true,"text":[{"text":"    let test = bin_lib_no_cfg_test::LibCfgTestStruct { };","highlight_start":37,"highlight_end":53}],"label":"not found in `bin_lib_no_cfg_test`","suggested_replacement":null,"expansion":null}],"children":[],"rendered":null}
test test::test_bin_lib_project_no_cfg_test ... ok
test test::test_bin_lib_project ... ok
test test::test_completion ... ok
test test::test_find_all_refs ... ok
test test::test_find_all_refs_no_cfg_test ... ok
test test::test_multiple_binaries ... ok
test test::test_parse_error_on_malformed_input ... ok
test test::test_reformat ... ok
test test::test_reformat_with_range ... ok
test test::test_simple_workspace ... ok
test test::test_borrow_error ... FAILED
failures:
---- test::test_borrow_error stdout ----
	thread 'test::test_borrow_error' panicked at 'Hit timeout', src\tools\rls\src\test\harness.rs:142:12
failures:
    test::test_borrow_error
test result: FAILED. 13 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out

cc @rls

[Mark-Simulacrum]

Also hit this on Travis (same test) in #43430.

[nrc]

cc me

[SimonSapin]

This is causing lots of CI failures. Should this test be disabled until a fix can be found?

[Mark-Simulacrum]

We believe a fix is pending in #43485, once that lands we should be good to go.