Rollup merge of rust-lang#52853 - RalfJung:bootstrap-help, r=alexcric…

…hton

Improve bootstrap help on stages

Cc @eddyb

src/bootstrap/flags.rs

@@ -121,7 +121,10 @@ To learn more about a subcommand, run `./x.py <subcommand> -h`"
  opts.optmulti("", "exclude", "build paths to exclude", "PATH");
  opts.optopt("", "on-fail", "command to run on failure", "CMD");
  opts.optflag("", "dry-run", "dry run; don't build anything");
- opts.optopt("", "stage", "stage to build", "N");
+ opts.optopt("", "stage",
+ "stage to build (indicates compiler to use/test, e.g. stage 0 uses the \
+ bootstrap compiler, stage 1 the stage 0 rustc artifacts, etc.)",
+ "N");
  opts.optmulti("", "keep-stage", "stage(s) to keep without recompiling", "N");
  opts.optopt("", "src", "path to the root of the rust checkout", "DIR");
  opts.optopt("j", "jobs", "number of jobs to run in parallel", "JOBS");
@@ -258,7 +261,7 @@ Arguments:
 
  ./x.py build --stage 1 src/libtest
 
- This will first build everything once (like --stage 0 without further
+ This will first build everything once (like `--stage 0` without further
  arguments would), and then use the compiler built in stage 0 to build
  src/libtest and its dependencies.
  Once this is done, build/$ARCH/stage1 contains a usable compiler.",
@@ -290,10 +293,14 @@ Arguments:
 
  ./x.py test src/test/run-pass
  ./x.py test src/libstd --test-args hash_map
- ./x.py test src/libstd --stage 0
+ ./x.py test src/libstd --stage 0 --no-doc
  ./x.py test src/test/ui --bless
  ./x.py test src/test/ui --compare-mode nll
 
+ Note that `test src/test/* --stage N` does NOT depend on `build src/rustc --stage N`;
+ just like `build src/libstd --stage N` it tests the compiler produced by the previous
+ stage.
+
  If no arguments are passed then the complete artifacts for that stage are
  compiled and tested.