rust/tests/run-make/unstable-flag-required/output-format-json.stderr

error: the -Z unstable-options flag must be passed to enable --output-format for documentation generation (see https://github.com/rust-lang/rust/issues/76578)
Fix handling of `--output-format json` flag - Don't treat it as deprecated on stable and beta channels. Before, it would give confusing and incorrect output: ``` warning: the 'output-format' flag is considered deprecated \| = warning: see issue #44136 <https://github.com/rust-lang/rust/issues/44136> for more information error: json output format isn't supported for doc generation ``` Both of those are wrong: output-format isn't deprecated, and json output is supported. - Require -Z unstable-options for `--output-format json` Previously, it was allowed by default on nightly, which made it hard to realize the flag wouldn't be accepted on beta or stable. Note that this still allows `--output-format html`, which has been stable since 1.0. - Remove unnecessary double-checking of the feature gate when parsing the output format - Add custom run-make test since compiletest passes -Zunstable-options by default 2021-02-24 15:16:49 -06:00			`error: the -Z unstable-options flag must be passed to enable --output-format for documentation generation (see https://github.com/rust-lang/rust/issues/76578)`