Rollup merge of #141646 - jieyouxu:distcheck, r=Mark-Simulacrum

Document what `distcheck` is intended to exercise

Or at least attempt to.

Closes rust-lang/rust#141387.

cc `@marcoieni` (re. [#t-infra/bootstrap > Speed up distcheck](https://rust-lang.zulipchat.com/#narrow/channel/326414-t-infra.2Fbootstrap/topic/Speed.20up.20distcheck/with/520208870))
r? `@Mark-Simulacrum` (as you may have some clues about if this is accurate)

1 files changed, 8 insertions, 1 deletions

diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index acd6fc47705..bb682751a2e 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -2964,7 +2964,14 @@ impl Step for Distcheck {
         run.builder.ensure(Distcheck);
     }
 
-    /// Runs "distcheck", a 'make check' from a tarball
+    /// Runs `distcheck`, which is a collection of smoke tests:
+    ///
+    /// - Run `make check` from an unpacked dist tarball to make sure we can at the minimum run
+    ///   check steps from those sources.
+    /// - Check that selected dist components (`rust-src` only at the moment) at least have expected
+    ///   directory shape and crate manifests that cargo can generate a lockfile from.
+    ///
+    /// FIXME(#136822): dist components are under-tested.
     fn run(self, builder: &Builder<'_>) {
         builder.info("Distcheck");
         let dir = builder.tempdir().join("distcheck");