Use merge-base diffing in link-check lints

.ci/scripts/tests/test_link_check_diff_selection.py

@@ -0,0 +1,111 @@
+import os
+import stat
+import subprocess
+import sys
+import tempfile
+import textwrap
+import unittest
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[3]
+
+
+@unittest.skipUnless(sys.platform == "linux", "The scripts under test run on Linux runners only")
+class TestLinkCheckDiffSelection(unittest.TestCase):
+    def setUp(self) -> None:
+        self._tmpdir = tempfile.TemporaryDirectory()
+        self.repo = Path(self._tmpdir.name)
+        self.run_cmd("git init -b main")
+        self.run_cmd('git config user.name "Test User"')
+        self.run_cmd('git config user.email "test@example.com"')
+        self.write("README.md", "base\n")
+        self.write("docs/feature-target.md", "feature target\n")
+        self.write("docs/main-target.md", "main target\n")
+        self.run_cmd("git add README.md docs/feature-target.md docs/main-target.md")
+        self.run_cmd('git commit -m "base"')
+        self.run_cmd("git checkout -b feature")
+
+    def tearDown(self) -> None:
+        self._tmpdir.cleanup()
+
+    def run_cmd(
+        self, command: str, env: dict[str, str] | None = None
+    ) -> subprocess.CompletedProcess[str]:
+        return subprocess.run(
+            command,
+            shell=True,
+            cwd=self.repo,
+            env=env,
+            check=True,
+            text=True,
+            capture_output=True,
+        )
+
+    def write(self, relative_path: str, content: str) -> None:
+        path = self.repo / relative_path
+        path.parent.mkdir(parents=True, exist_ok=True)
+        path.write_text(content)
+
+    def create_diverged_history(
+        self, feature_path: str, feature_content: str, main_path: str, main_content: str
+    ) -> tuple[str, str]:
+        self.write(feature_path, feature_content)
+        self.run_cmd(f"git add {feature_path}")
+        self.run_cmd('git commit -m "feature change"')
+        head_sha = self.run_cmd("git rev-parse HEAD").stdout.strip()
+
+        self.run_cmd("git checkout main")
+        self.write(main_path, main_content)
+        self.run_cmd(f"git add {main_path}")
+        self.run_cmd('git commit -m "main change"')
+        base_sha = self.run_cmd("git rev-parse HEAD").stdout.strip()
+        return base_sha, head_sha
+
+    def make_fake_curl(self) -> dict[str, str]:
+        bin_dir = self.repo / "bin"
+        bin_dir.mkdir()
+        curl = bin_dir / "curl"
+        curl.write_text("#!/bin/sh\nprintf '200'\n")
+        curl.chmod(curl.stat().st_mode | stat.S_IEXEC)
+        env = os.environ.copy()
+        env["PATH"] = f"{bin_dir}:{env['PATH']}"
+        return env
+
+    def test_lint_urls_uses_merge_base_for_changed_lines(self) -> None:
+        base_sha, head_sha = self.create_diverged_history(
+            "feature.md",
+            "https://example.com/feature\n",
+            "main.md",
+            "https://example.com/main\n",
+        )
+
+        result = self.run_cmd(
+            f"bash {REPO_ROOT / 'scripts' / 'lint_urls.sh'} {base_sha} {head_sha}",
+            env=self.make_fake_curl(),
+        )
+
+        self.assertIn("feature.md", result.stdout)
+        self.assertNotIn("main.md", result.stdout)
+
+    def test_lint_xrefs_uses_merge_base_for_changed_lines(self) -> None:
+        base_sha, head_sha = self.create_diverged_history(
+            "feature.md",
+            textwrap.dedent(
+                """\
+                [feature](docs/feature-target.md)
+                """
+            ),
+            "main.md",
+            textwrap.dedent(
+                """\
+                [main](docs/main-target.md)
+                """
+            ),
+        )
+
+        result = self.run_cmd(
+            f"bash {REPO_ROOT / 'scripts' / 'lint_xrefs.sh'} {base_sha} {head_sha}"
+        )
+
+        self.assertIn("feature.md", result.stdout)
+        self.assertNotIn("main.md", result.stdout)

.github/workflows/_link_check.yml

@@ -29,7 +29,7 @@ jobs:
           args=()
           # A push creating a tag or branch reports an all zero SHA no remote can serve.
           if [ -n "$BASE_REF" ] && [ "$BASE_REF" != "0000000000000000000000000000000000000000" ]; then
-            git fetch --no-tags --depth=1 origin "$BASE_REF"
+            git fetch --no-tags origin "$BASE_REF"
             args=("$BASE_REF" "$HEAD_REF")
           fi
           ./scripts/lint_urls.sh "${args[@]}" || {

scripts/lint_xrefs.sh

@@ -35,8 +35,8 @@ done < <(
     ':(exclude,glob)**/third_party/**'
   )
   if [ $# -eq 2 ]; then
-    for filename in $(git diff --name-only --unified=0 "$1..$2"); do
-      git diff --unified=0 "$1..$2" -- "$filename" "${excludes[@]}" \
+    for filename in $(git diff --name-only --unified=0 "$1...$2"); do
+      git diff --unified=0 "$1...$2" -- "$filename" "${excludes[@]}" \
         | grep -E '^\+' \
         | grep -Ev '^\+\+\+' \
         | perl -nle 'print for m#'"$pattern"'#g' \