Rollup merge of #70698 - nikomatsakis:x-py-json-output, r=Mark-Simulacrum

bootstrap: add `--json-output` for rust-analyzer

Motivation is that this allows us to customize rust-analyzer's "cargo watch" integration to run x.py. You simply have to set the command to run to be `x.py --json-output`

r? @Mark-Simulacrum -- feel free to make changes, this is quick and dirty for sure

src/bootstrap/compile.rs

@@ -911,7 +911,11 @@ pub fn stream_cargo(
     }
     // Instruct Cargo to give us json messages on stdout, critically leaving
     // stderr as piped so we can get those pretty colors.
-    let mut message_format = String::from("json-render-diagnostics");
+    let mut message_format = if builder.config.json_output {
+        String::from("json")
+    } else {
+        String::from("json-render-diagnostics")
+    };
     if let Some(s) = &builder.config.rustc_error_format {
         message_format.push_str(",json-diagnostic-");
         message_format.push_str(s);

src/bootstrap/config.rs

@@ -48,6 +48,7 @@ pub struct Config {
     pub ignore_git: bool,
     pub exclude: Vec<PathBuf>,
     pub rustc_error_format: Option<String>,
+    pub json_output: bool,
     pub test_compare_mode: bool,
     pub llvm_libunwind: bool,
 
@@ -415,6 +416,7 @@ pub fn parse(args: &[String]) -> Config {
         let mut config = Config::default_opts();
         config.exclude = flags.exclude;
         config.rustc_error_format = flags.rustc_error_format;
+        config.json_output = flags.json_output;
         config.on_fail = flags.on_fail;
         config.stage = flags.stage;
         config.jobs = flags.jobs.map(threads_from_config);

src/bootstrap/flags.rs

@@ -31,6 +31,7 @@ pub struct Flags {
     pub incremental: bool,
     pub exclude: Vec<PathBuf>,
     pub rustc_error_format: Option<String>,
+    pub json_output: bool,
     pub dry_run: bool,
 
     // This overrides the deny-warnings configuration option,
@@ -156,6 +157,7 @@ pub fn parse(args: &[String]) -> Flags {
             "VALUE",
         );
         opts.optopt("", "error-format", "rustc error format", "FORMAT");
+        opts.optflag("", "json-output", "use message-format=json");
         opts.optopt(
             "",
             "llvm-skip-rebuild",
@@ -503,6 +505,7 @@ pub fn parse(args: &[String]) -> Flags {
             dry_run: matches.opt_present("dry-run"),
             on_fail: matches.opt_str("on-fail"),
             rustc_error_format: matches.opt_str("error-format"),
+            json_output: matches.opt_present("json-output"),
             keep_stage: matches
                 .opt_strs("keep-stage")
                 .into_iter()