Add tests for merge rules validation engine

Adds comprehensive test coverage for the merge rules feature:

- test/merge_rules/yaml_parsing.py.test: YAML parsing tests
- test/merge_rules/pattern_matching.py.test: fnmatch pattern tests
- test/merge_rules/approval_validation.py.test: approver validation tests
- test/merge_rules/check_validation.py.test: CI check validation tests
- test/merge_rules/ignore_flaky.py.test: ignore_flaky_failures flag tests

Adds land command integration tests:
- test/land/validate_rules_fail.py.test: validation blocks land
- test/land/validate_rules_pass.py.test: validation passes and lands
- test/land/dry_run.py.test: dry run mode validates but doesn't land

Also adds helper functions to test_prelude.py:
- set_pr_files, set_pr_reviews, set_pr_check_runs
- Updated gh_land to support validate_rules, dry_run, comment_on_failure flags

Co-authored-by: Cursor <cursoragent@cursor.com>
ghstack-source-id: 4a5247e
ghstack-comment-id: 3838814339
Pull-Request: #321

Author: seemethere

src/ghstack/test_prelude.py

@@ -53,6 +53,9 @@
     "get_github",
     "get_pr_reviewers",
     "get_pr_labels",
+    "set_pr_files",
+    "set_pr_reviews",
+    "set_pr_check_runs",
     "tick",
     "captured_output",
 ]
@@ -225,14 +228,25 @@ def gh_submit(
     return r
 
 
-def gh_land(pull_request: str) -> None:
+def gh_land(
+    pull_request: str,
+    *,
+    validate_rules: bool = False,
+    dry_run: bool = False,
+    comment_on_failure: bool = False,
+    rules_file: Optional[str] = None,
+) -> None:
     self = CTX
     return ghstack.land.main(
         remote_name="origin",
         pull_request=pull_request,
         github=self.github,
         sh=self.sh,
         github_url="github.com",
+        validate_rules=validate_rules,
+        dry_run=dry_run,
+        comment_on_failure=comment_on_failure,
+        rules_file=rules_file,
     )
 
 
@@ -412,6 +426,36 @@ def get_pr_labels(pr_number: int) -> List[str]:
     return pr.labels
 
 
+def set_pr_files(pr_number: int, files: List[str]) -> None:
+    """Set the list of changed files for a PR."""
+    github = get_github()
+    repo = github.state.repository("pytorch", "pytorch")
+    pr = github.state.pull_request(repo, ghstack.github_fake.GitHubNumber(pr_number))
+    pr.files = files
+
+
+def set_pr_reviews(pr_number: int, reviews: List[Tuple[str, str]]) -> None:
+    """Set reviews for a PR. reviews is list of (user, state) tuples."""
+    github = get_github()
+    repo = github.state.repository("pytorch", "pytorch")
+    pr = github.state.pull_request(repo, ghstack.github_fake.GitHubNumber(pr_number))
+    pr.reviews = [
+        ghstack.github_fake.PullRequestReview(user=u, state=s) for u, s in reviews
+    ]
+
+
+def set_pr_check_runs(
+    pr_number: int, checks: List[Tuple[str, str, Optional[str]]]
+) -> None:
+    """Set check runs for a PR. checks is list of (name, status, conclusion) tuples."""
+    github = get_github()
+    repo = github.state.repository("pytorch", "pytorch")
+    pr = github.state.pull_request(repo, ghstack.github_fake.GitHubNumber(pr_number))
+    pr.check_runs = [
+        ghstack.github_fake.CheckRun(name=n, status=s, conclusion=c) for n, s, c in checks
+    ]
+
+
 def assert_eq(a: Any, b: Any) -> None:
     assert a == b, f"{a} != {b}"
 

test/land/dry_run.py.test

@@ -0,0 +1,49 @@
+from ghstack.test_prelude import *
+
+import os
+import tempfile
+import ghstack.merge_rules
+from ghstack.github_fake import GitHubNumber, PullRequestReview, CheckRun
+
+init_test()
+commit("A")
+(diff,) = gh_submit("Initial 1")
+pr_url = diff.pr_url
+
+# Set up PR with files, approvals, and passing checks
+github = get_github()
+repo = github.state.repository("pytorch", "pytorch")
+pr = github.state.pull_request(repo, GitHubNumber(500))
+pr.files = ["src/core/module.py"]
+pr.reviews = [PullRequestReview(user="maintainer1", state="APPROVED")]
+pr.check_runs = [CheckRun(name="CI", status="completed", conclusion="success")]
+
+# Create a temporary rules file
+rules_content = """
+- name: core-changes
+  patterns: ["src/core/*"]
+  approved_by: ["maintainer1"]
+  mandatory_checks_name: ["CI"]
+"""
+
+with tempfile.NamedTemporaryFile(mode="w", suffix=".yaml", delete=False) as f:
+    f.write(rules_content)
+    rules_file = f.name
+
+try:
+    # Get the initial state of master
+    initial_log = get_upstream_sh().git("log", "--oneline", "master")
+    
+    # Dry run should NOT land the commit
+    gh_land(pr_url, validate_rules=True, dry_run=True, rules_file=rules_file)
+    
+    # Verify master is unchanged (no commit was landed)
+    final_log = get_upstream_sh().git("log", "--oneline", "master")
+    assert_eq(initial_log, final_log)
+    
+    # The PR should still be open
+    assert_eq(pr.closed, False)
+finally:
+    os.unlink(rules_file)
+
+ok()

test/land/validate_rules_fail.py.test

@@ -0,0 +1,46 @@
+from ghstack.test_prelude import *
+
+import os
+import tempfile
+import ghstack.merge_rules
+from ghstack.github_fake import GitHubNumber
+
+init_test()
+commit("A")
+(diff,) = gh_submit("Initial 1")
+pr_url = diff.pr_url
+
+# Set up PR with files but no approvals
+github = get_github()
+repo = github.state.repository("pytorch", "pytorch")
+pr = github.state.pull_request(repo, GitHubNumber(500))
+pr.files = ["src/core/module.py"]
+pr.reviews = []  # No reviews
+
+# Create a temporary rules file
+rules_content = """
+- name: core-changes
+  patterns: ["src/core/*"]
+  approved_by: ["maintainer1"]
+  mandatory_checks_name: []
+"""
+
+with tempfile.NamedTemporaryFile(mode="w", suffix=".yaml", delete=False) as f:
+    f.write(rules_content)
+    rules_file = f.name
+
+try:
+    # Attempt to land with validation - should raise MergeValidationError
+    assert_expected_raises_inline(
+        ghstack.merge_rules.MergeValidationError,
+        lambda: gh_land(pr_url, validate_rules=True, rules_file=rules_file),
+        """\
+Merge validation failed for PR #500
+Rule: core-changes
+Errors:
+  - Missing required approval from: maintainer1""",
+    )
+finally:
+    os.unlink(rules_file)
+
+ok()

test/land/validate_rules_pass.py.test

@@ -0,0 +1,47 @@
+from ghstack.test_prelude import *
+
+import os
+import tempfile
+import ghstack.merge_rules
+from ghstack.github_fake import GitHubNumber, PullRequestReview, CheckRun
+
+init_test()
+commit("A")
+(diff,) = gh_submit("Initial 1")
+pr_url = diff.pr_url
+
+# Set up PR with files, approvals, and passing checks
+github = get_github()
+repo = github.state.repository("pytorch", "pytorch")
+pr = github.state.pull_request(repo, GitHubNumber(500))
+pr.files = ["src/core/module.py"]
+pr.reviews = [PullRequestReview(user="maintainer1", state="APPROVED")]
+pr.check_runs = [CheckRun(name="CI", status="completed", conclusion="success")]
+
+# Create a temporary rules file
+rules_content = """
+- name: core-changes
+  patterns: ["src/core/*"]
+  approved_by: ["maintainer1"]
+  mandatory_checks_name: ["CI"]
+"""
+
+with tempfile.NamedTemporaryFile(mode="w", suffix=".yaml", delete=False) as f:
+    f.write(rules_content)
+    rules_file = f.name
+
+try:
+    # Land with validation - should succeed
+    gh_land(pr_url, validate_rules=True, rules_file=rules_file)
+    
+    # Verify the commit was landed
+    assert_expected_inline(
+        get_upstream_sh().git("log", "--oneline", "master"),
+        """\
+d518c9f Commit A (#500)
+dc8bfe4 Initial commit""",
+    )
+finally:
+    os.unlink(rules_file)
+
+ok()

test/merge_rules/approval_validation.py.test

@@ -0,0 +1,93 @@
+from ghstack.test_prelude import *
+
+import ghstack.merge_rules
+from ghstack.github_fake import PullRequestReview, GitHubNumber
+
+init_test()
+commit("A")
+(A,) = gh_submit("Initial 1")
+
+# Set up PR with files and NO approval
+github = get_github()
+repo = github.state.repository("pytorch", "pytorch")
+pr = github.state.pull_request(repo, GitHubNumber(500))
+pr.files = ["src/core/module.py"]
+pr.reviews = []  # No reviews yet
+
+rules = [
+    ghstack.merge_rules.MergeRule(
+        name="core",
+        patterns=["src/core/*"],
+        approved_by=["maintainer1"],
+        mandatory_checks_name=[],
+    )
+]
+
+validator = ghstack.merge_rules.MergeValidator(github, "pytorch", "pytorch")
+result = validator.validate_pr(500, rules)
+
+# Should fail - missing approval
+assert_eq(result.valid, False)
+assert "Missing required approval" in result.errors[0]
+
+# Add approval from wrong user - should still fail
+pr.reviews = [PullRequestReview(user="random_user", state="APPROVED")]
+result = validator.validate_pr(500, rules)
+assert_eq(result.valid, False)
+
+# Add approval from required user - should pass
+pr.reviews = [PullRequestReview(user="maintainer1", state="APPROVED")]
+result = validator.validate_pr(500, rules)
+assert_eq(result.valid, True)
+
+# Test multiple required approvers - any one should work
+rules = [
+    ghstack.merge_rules.MergeRule(
+        name="core",
+        patterns=["src/core/*"],
+        approved_by=["maintainer1", "maintainer2"],
+        mandatory_checks_name=[],
+    )
+]
+
+pr.reviews = [PullRequestReview(user="maintainer2", state="APPROVED")]
+result = validator.validate_pr(500, rules)
+assert_eq(result.valid, True)
+
+# Test that CHANGES_REQUESTED doesn't count as approval
+pr.reviews = [PullRequestReview(user="maintainer1", state="CHANGES_REQUESTED")]
+result = validator.validate_pr(500, rules)
+assert_eq(result.valid, False)
+
+# Test that latest review state wins
+pr.reviews = [
+    PullRequestReview(user="maintainer1", state="APPROVED"),
+    PullRequestReview(user="maintainer1", state="CHANGES_REQUESTED"),
+]
+result = validator.validate_pr(500, rules)
+assert_eq(result.valid, False)
+
+# Re-approval after changes_requested should work
+pr.reviews = [
+    PullRequestReview(user="maintainer1", state="CHANGES_REQUESTED"),
+    PullRequestReview(user="maintainer1", state="APPROVED"),
+]
+result = validator.validate_pr(500, rules)
+assert_eq(result.valid, True)
+
+# Test "any" special approver - any approval should work
+rules = [
+    ghstack.merge_rules.MergeRule(
+        name="any-approval",
+        patterns=["src/*"],
+        approved_by=["any"],
+        mandatory_checks_name=[],
+    )
+]
+
+pr.files = ["src/module.py"]
+pr.reviews = [PullRequestReview(user="anyone", state="APPROVED")]
+result = validator.validate_pr(500, rules)
+assert_eq(result.valid, True)
+
+ok()