…_output, r=pietroalbini

Bugfix: avoid panic on invalid json output from libtest

rust-lang#108659 introduces a custom test display implementation. It does so by using libtest to output json. The stdout is read and parsed; The code trims the line read and checks whether it starts with a `{` and ends with a `}`. If so, it concludes that it must be a json encoded `Message`. Unfortunately, this does not work in all cases:

- This assumes that tests running with `--nocapture` will never start and end lines with `{` and `}` characters
- Output is generated by issuing multiple `write_message` [statements](https://github.com/rust-lang/rust/blob/master/library/test/src/formatters/json.rs#L33-L60). Where only the last one issues a `\n`. This likely results in a race condition as we see multiple json outputs on the same line when running tests for the `x86_64-fortanix-unknown-sgx` target:
```
10:21:04 �[0m�[0m�[1m�[32m     Running�[0m tests/run-time-detect.rs (build/x86_64-unknown-linux-gnu/stage1-std/x86_64-fortanix-unknown-sgx/release/deps/run_time_detect-8c66026bd4b1871a)
10:21:04
10:21:04 running 1 tests
10:21:04 test x86_all ... ok
10:21:04 �[0m�[0m�[1m�[32m     Running�[0m tests/thread.rs (build/x86_64-unknown-linux-gnu/stage1-std/x86_64-fortanix-unknown-sgx/release/deps/thread-ed5456a7d80a6193)
10:21:04 thread 'main' panicked at 'failed to parse libtest json output; error: trailing characters at line 1 column 135, line: "{ \"type\": \"suite\", \"event\": \"ok\", \"passed\": 1, \"failed\": 0, \"ignored\": 0, \"measured\": 0, \"filtered_out\": 0, \"exec_time\": 0.000725911 }{ \"type\": \"suite\", \"event\": \"started\", \"test_count\": 1 }\n"', render_tests.rs:108:25
```

This PR implements a partial fix by being much more conservative of what it asserts is a valid json encoded `Message`. This prevents panics, but still does not resolve the race condition. A discussion is needed where this race condition comes from exactly and how it best can be avoided.

cc: `@jethrogb,` `@pietroalbini`

…huss

Validate `ignore` and `only` compiletest directive, and add human-readable ignore reasons

This PR adds strict validation for the `ignore` and `only` compiletest directives, failing if an unknown value is provided to them. Doing so uncovered 79 tests in `tests/ui` that had invalid directives, so this PR also fixes them.

Finally, this PR adds human-readable ignore reasons when tests are ignored due to `ignore` or `only` directives, like *"only executed when the architecture is aarch64"* or *"ignored when the operative system is windows"*. This was the original reason why I started working on this PR and rust-lang#108659, as we need both of them for Ferrocene.

The PR is a draft because the code is extremely inefficient: it calls `rustc --print=cfg --target $target` for every rustc target (to gather the list of allowed ignore values), which on my system takes between 4s and 5s, and performs a lot of allocations of constant values. I'll fix both of them in the coming days.

r? `@ehuss`

fix running Miri tests

This partially reverts rust-lang#108659 to fix rust-lang#110102: the Miri test runner does not support any flags, they are interpreted as filters instead which leads to no tests being run.

I have not checked any of the other test runners for whether they are having any trouble with these flags.

Cc `@pietroalbini` `@Mark-Simulacrum` `@jyn514`

fix running Miri tests

This partially reverts rust-lang/rust#108659 to fix rust-lang/rust#110102: the Miri test runner does not support any flags, they are interpreted as filters instead which leads to no tests being run.

I have not checked any of the other test runners for whether they are having any trouble with these flags.

Cc `@pietroalbini` `@Mark-Simulacrum` `@jyn514`

…ynchronization, r=pietroalbini

Ensure test library issues json string line-by-line

rust-lang#108659 introduces a custom test display implementation. It does so by using libtest to output json. The stdout is read line by line and parsed. The code trims the line read and checks whether it starts with a `{` and ends with a `}`.

Unfortunately, there is a race condition in how json data is written to stdout. The `write_message` function calls `self.out.write_all` repeatedly to write a buffer that contains (partial) json data, or a new line. There is no lock around the `self.out.write_all` functions. Similarly, the `write_message` function itself is called with only partial json data. As these functions are called from concurrent threads, this may result in json data ending up on the same stdout line. This PR avoids this by buffering the complete json data before issuing a single `self.out.write_all`.

(rust-lang#109484 implemented a partial fix for this issue; it only avoids that failed json parsing would result in a panic.)

cc: `@jethrogb,` `@pietroalbini`

compiletest: Remove the `--logfile` flag

This flag is deprecated in libtest (rust-lang#134283), and there's no evidence in-tree of this flag actually being passed to compiletest.

For detailed information about test results, bootstrap parses JSON output from compiletest instead (rust-lang#108659).

As part of my experimental work on removing the libtest dependency from compiletest, it's useful to be able to disconnect libtest functionality that isn't needed.

Rollup merge of rust-lang#139528 - Zalathar:no-logfile, r=jieyouxu

compiletest: Remove the `--logfile` flag

This flag is deprecated in libtest (rust-lang#134283), and there's no evidence in-tree of this flag actually being passed to compiletest.

For detailed information about test results, bootstrap parses JSON output from compiletest instead (rust-lang#108659).

As part of my experimental work on removing the libtest dependency from compiletest, it's useful to be able to disconnect libtest functionality that isn't needed.