…iaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#109355 (Fix bad suggestion for clone/is_some in field init shorthand)
 - rust-lang#109484 (Bugfix: avoid panic on invalid json output from libtest)
 - rust-lang#109539 (Refactor `find_*_stability` functions)
 - rust-lang#109542 (rustdoc: clean up `storage.js`)
 - rust-lang#109545 (Deeply check well-formedness of return-position `impl Trait` in trait)
 - rust-lang#109568 (miri: fix raw pointer dyn receivers)
 - rust-lang#109570 (Add GUI test for "Auto-hide item methods' documentation" setting)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

…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`