From 6a5b03d88880e1771654c470fd54d4eb52191418 Mon Sep 17 00:00:00 2001
From: Richard McDaniel <1130888+rmcdaniel@users.noreply.github.com>
Date: Thu, 5 Nov 2026 04:23:35 +0000
Subject: [PATCH] Pin visual classification to one comparison commit

---
 scripts/visual_evidence.py    |  3 +++
 tests/test_visual_evidence.py | 48 +++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/scripts/visual_evidence.py b/scripts/visual_evidence.py
index 53a470a..d6d0808 100644
--- a/scripts/visual_evidence.py
+++ b/scripts/visual_evidence.py
@@ -86,6 +86,8 @@ def classify_changes(
     base_ref: str | None = None,
     profile_name: str | None = None,
 ) -> dict[str, list[str]]:
+    if base_ref:
+        base_ref = comparison_commit(root, base_ref)
     extensions = tuple(policy["customer_facing_extensions"])
     matches: dict[str, set[str]] = {}
     for path in paths:
@@ -329,6 +331,7 @@ def main() -> None:
     policy = load_json(args.policy, "visual evidence policy")
     paths = list(args.changed_file)
     if args.base_ref:
+        args.base_ref = comparison_commit(root, args.base_ref)
         paths.extend(changed_paths(root, args.base_ref))
     if not paths:
         raise SystemExit("provide --base-ref or at least one --changed-file")
diff --git a/tests/test_visual_evidence.py b/tests/test_visual_evidence.py
index e7646f6..57aaaaf 100644
--- a/tests/test_visual_evidence.py
+++ b/tests/test_visual_evidence.py
@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import contextlib
+import io
 import json
 import re
 import subprocess
@@ -7,10 +9,12 @@
 import unittest
 from pathlib import Path
 from typing import Any
+from unittest.mock import patch
 
 import yaml
 from jsonschema import Draft202012Validator
 
+from scripts import visual_evidence
 from scripts.visual_evidence import (
     VisualEvidenceError,
     changed_paths,
@@ -75,6 +79,50 @@ def test_missing_and_noncommit_refs_refuse(self):
                     with self.assertRaises(VisualEvidenceError):
                         function(*arguments)
 
+    def deleted_stylesheets(self, contents):
+        for name, content in contents.items():
+            (self.root / name).write_text(content)
+        self.git("add", ".")
+        self.git("commit", "-qm", "comparison stylesheets")
+        self.git("branch", "-f", "comparison-base")
+        for name in contents:
+            (self.root / name).unlink()
+        self.git("add", ".")
+        self.git("commit", "-qm", "remove comparison stylesheets")
+
+    def move_branch_after_resolution(self):
+        original = visual_evidence.comparison_commit
+
+        def resolve(root, reference):
+            commit = original(root, reference)
+            if reference == "comparison-base":
+                self.git("update-ref", "refs/heads/comparison-base", "HEAD")
+            return commit
+
+        return patch.object(visual_evidence, "comparison_commit", side_effect=resolve)
+
+    def modal_policy(self):
+        return {"customer_facing_extensions": [".css"],
+                "interactions": {"modal": {"content_patterns": [r"\.modal"]}}}
+
+    def test_cli_keeps_deleted_content_when_branch_moves_after_diff_resolution(self):
+        self.deleted_stylesheets({"source.css": ".modal { display: block; }\n"})
+        policy = self.output / "policy.json"
+        policy.write_text(json.dumps(self.modal_policy()))
+        arguments = ["visual_evidence", "--policy", str(policy), "classify",
+                     "--root", str(self.root), "--base-ref", "comparison-base"]
+        output = io.StringIO()
+        with self.move_branch_after_resolution(), patch("sys.argv", arguments), contextlib.redirect_stdout(output):
+            visual_evidence.main()
+        self.assertEqual({"classification": {"modal": ["source.css"]}}, json.loads(output.getvalue()))
+
+    def test_classifier_keeps_one_baseline_when_branch_moves_between_files(self):
+        self.deleted_stylesheets({"a.css": "body { color: black; }\n",
+                                  "b.css": ".modal { display: block; }\n"})
+        with self.move_branch_after_resolution():
+            result = classify_changes(self.root, ["a.css", "b.css"], self.modal_policy(), "comparison-base")
+        self.assertEqual({"modal": ["b.css"]}, result)
+
 
 class VisualEvidencePolicyTest(unittest.TestCase):
     def setUp(self) -> None: