Add typeshed diff link to changelog during release (#2957)

Co-authored-by: Claude <noreply@anthropic.com>

scripts/release.sh

@@ -32,6 +32,14 @@ case "${ruff_head}" in
 esac
 
 
+# Save the current typeshed source commit before updating ruff,
+# so we can generate a typeshed diff link for the changelog later.
+typeshed_commit_file="ruff/crates/ty_vendored/vendor/typeshed/source_commit.txt"
+old_typeshed_commit=""
+if [ -f "$typeshed_commit_file" ]; then
+    old_typeshed_commit=$(cat "$typeshed_commit_file")
+fi
+
 echo "Updating Ruff to the latest commit..."
 git -C ruff pull origin main
 git add ruff
@@ -46,5 +54,20 @@ cd "$project_root"
 uv run --isolated --only-group release \
     rooster release "$@"
 
+# If the typeshed source commit changed and the changelog mentions a typeshed
+# sync, append a link to the typeshed diff so reviewers can see what changed.
+if [ -n "$old_typeshed_commit" ] && [ -f "$typeshed_commit_file" ]; then
+    new_typeshed_commit=$(cat "$typeshed_commit_file")
+    if [ "$old_typeshed_commit" != "$new_typeshed_commit" ]; then
+        typeshed_diff_link="[Typeshed diff](https://github.com/python/typeshed/compare/${old_typeshed_commit}...${new_typeshed_commit})"
+        # Match lines like "- Sync vendored typeshed stubs ([#NNNN](...))".
+        # The pattern anchors on the trailing "))$" so it won't match lines
+        # that already have a typeshed diff link appended.
+        # Use a temp file instead of `sed -i` for macOS/Linux portability.
+        sed "s|\(- Sync vendored typeshed stubs (.*)\))$|\1). ${typeshed_diff_link}|" CHANGELOG.md > CHANGELOG.md.tmp
+        mv CHANGELOG.md.tmp CHANGELOG.md
+    fi
+fi
+
 "${script_root}/autogenerate_files.sh"
 git add ./docs/reference