Unrolled build for rust-lang#134528

Rollup merge of rust-lang#134528 - jieyouxu:fix-rustc-bootstrap-test, r=Kobzol

opt-dist: propagate channel info to bootstrap

Fixes rust-lang#133503.

Previously, `tests/ui/bootstrap/rustc_bootstap.rs` [sic] failed during [beta bump](rust-lang#133447 (comment)) in opt-dist tests. This is because:

- `opt-dist` tried to run `./x test` against beta-channel dist `rustc` through `bootstrap`.
- The dist build produced during the beta bump produces a `rustc` which correctly thinks that it is a beta compiler based on `src/ci/channel` info.
- `opt-dist` tries to run `./x test` on the beta `rustc` from the dist build, but without specifying channel through a synthetic `config.toml`, so `bootstrap` tells `compiletest` that we're on the `nightly` channel (by default).
- Now there's a channel mismatch: `compiletest` believes the `rustc` under test is a *nightly* rustc, but the `rustc` under test actually considers itself a *beta* rustc. This means that `//@ only-nightly` will be satisfied yet the test will fail as the *beta* rustc is not a *nightly* rustc.

This PR:

- Fixes the test failure during beta bump (i.e. rust-lang#133503) by having `opt-dist` faithfully report the channel of the dist `rustc` being tested (i.e. "beta" in a beta bump PR). This will properly make the test be ignored during beta bump as the `rustc` under test is not a *nightly* rustc.
- Fixes the test name `rustc_bootstap.rs` -> `rustc_bootstrap.rs`. No more stapping.
- Slightly adjusts the doc comment in the test to make it more clear.

I ran a try-job against the beta branch (explicitly running the opt-dist tests by modifying the job definition) with these changes in rust-lang#134131, and it appears that the try-job was [successful](rust-lang#134131 (comment)). The two commits in this PR are cherry-picked from rust-lang#134131, with the test commit slightly modified (to also adjust the test comments).

r? `@Kobzol` (or compiler or bootstrap or infra I guess?)

src/tools/opt-dist/src/tests.rs

@@ -25,6 +25,8 @@ pub fn run_tests(env: &Environment) -> anyhow::Result<()> {
     let host_triple = env.host_tuple();
     let version = find_dist_version(&dist_dir)?;
 
+    let channel = version_to_channel(&version);
+
     // Extract rustc, libstd, cargo and src archives to create the optimized sysroot
     let rustc_dir = extract_dist_dir(&format!("rustc-{version}-{host_triple}"))?.join("rustc");
     let libstd_dir = extract_dist_dir(&format!("rust-std-{version}-{host_triple}"))?
@@ -61,9 +63,13 @@ pub fn run_tests(env: &Environment) -> anyhow::Result<()> {
     assert!(llvm_config.is_file());
 
     let config_content = format!(
-        r#"profile = "user"
+        r#"
+profile = "user"
 change-id = 115898
 
+[rust]
+channel = "{channel}"
+
 [build]
 rustc = "{rustc}"
 cargo = "{cargo}"
@@ -116,3 +122,13 @@ fn find_dist_version(directory: &Utf8Path) -> anyhow::Result<String> {
         archive.strip_prefix("reproducible-artifacts-").unwrap().split_once('-').unwrap();
     Ok(version.to_string())
 }
+
+/// Roughly convert a version string (`nightly`, `beta`, or `1.XY.Z`) to channel string (`nightly`,
+/// `beta` or `stable`).
+fn version_to_channel(version_str: &str) -> &'static str {
+    match version_str {
+        "nightly" => "nightly",
+        "beta" => "beta",
+        _ => "stable",
+    }
+}

tests/ui/bootstrap/rustc_bootstap.rs → tests/ui/bootstrap/rustc_bootstrap.rs

@@ -1,5 +1,5 @@
-//! Check `RUSTC_BOOTSTRAP`'s behavior in relation to feature stability and what rustc considers
-//! itself to be (stable vs non-stable ).
+//! Check the compiler's behavior when the perma-unstable env var `RUSTC_BOOTSTRAP` is set in the
+//! environment in relation to feature stability and which channel rustc considers itself to be.
 //!
 //! `RUSTC_BOOTSTRAP` accepts:
 //!