feat(dist): add installer release metadata updater

ci/update-rustup-init.py

@@ -0,0 +1,43 @@
+import re
+import subprocess
+import sys
+import tomllib
+from pathlib import Path
+
+if len(sys.argv) != 2:
+    sys.exit("usage: python3 ci/update-rustup-init.py <remote>/<main|release/X.Y>")
+
+release_branch = sys.argv[1]
+if not re.fullmatch(r"[^/]+/(main|release/[0-9]+\.[0-9]+)", release_branch):
+    sys.exit("expected a remote-tracking main or release/X.Y branch")
+
+try:
+    # Resolve the source once so all metadata comes from the same commit, not HEAD.
+    commit, commit_date = subprocess.check_output(
+        ["git", "show", "--no-patch", "--format=%H %cs", f"refs/remotes/{release_branch}", "--"],
+        text=True,
+    ).split()
+    manifest = subprocess.check_output(
+        ["git", "show", f"{commit}:Cargo.toml"], text=True
+    )
+    version = tomllib.loads(manifest)["package"]["version"]
+except (subprocess.CalledProcessError, tomllib.TOMLDecodeError, KeyError) as error:
+    sys.exit(f"cannot read release metadata from {release_branch}: {error}")
+if not isinstance(version, str) or not re.fullmatch(r"[0-9]+\.[0-9]+\.[0-9]+", version):
+    sys.exit("expected package.version in the release source to be X.Y.Z")
+
+installer = Path("rustup-init.sh")
+contents = installer.read_bytes()
+metadata_lines = list(re.finditer(rb"^rustup-init .*$", contents, re.MULTILINE))
+if len(metadata_lines) != 1 or not re.fullmatch(
+    rb"rustup-init [0-9]+\.[0-9]+\.[0-9]+ \([0-9a-f]{7,40} [0-9]{4}-[0-9]{2}-[0-9]{2}\)",
+    metadata_lines[0].group(),
+):
+    sys.exit("expected exactly one rustup-init version/SHA/date line in rustup-init.sh")
+
+metadata = f"rustup-init {version} ({commit[:9]} {commit_date})"
+metadata_line = metadata_lines[0]
+updated = contents[:metadata_line.start()] + metadata.encode() + contents[metadata_line.end():]
+if updated != contents:
+    installer.write_bytes(updated)
+print(f"{release_branch} ({commit}): {metadata}")

doc/dev-guide/src/release-process.md

@@ -104,9 +104,15 @@ new [b]eta release or an official [r]elease:
    `$VER_NUM` already exists in `$BRANCH`'s `Cargo.toml` file. Then in a new PR
    targeting `$BRANCH`:
    1. Update `CHANGELOG.md` accordingly if necessary.
-   2. Update `rustup-init.sh` so that:
-      - The version number matches `$VER_NUM`.
-      - The commit shasum matches the latest commit on `$BRANCH`.
+   2. From the repository root, update `rustup-init.sh` using Python 3.11 or newer
+      and a freshly fetched remote-tracking `$BRANCH` (replace `upstream` with
+      your remote for `rust-lang/rustup`):
+      ```console
+      $ git fetch upstream
+      $ python3 ci/update-rustup-init.py upstream/$BRANCH
+      ```
+      This reads the version from that commit's `Cargo.toml` and its SHA and
+      commit date, even when the current branch contains release preparation changes.
    3. Update the test snapshot of `rustup-init.sh --help`.
       At the moment of writing, this is done by running:
       ```console