feat(finding): pluggable false-positive-history candidate filter

Add FINDING_FALSE_POSITIVE_HISTORY_CANDIDATE_FILTER_METHOD hook to
do_false_positive_history_batch. When configured, the per-finding candidate
list resolved by the deduplication algorithm is passed through the plugin
method before the FP decision, letting a plugin (Pro) narrow candidates by
fields excluded from the hash string but compared per pair (set-match tokens
on vulnerability_ids / CWEs). Resolved once via get_custom_method; a no-op
when unset, so default behavior is unchanged.

Tests: hook can suppress matches (drops candidates -> no FP replication) and
passthrough matches the default path.

Author: valentijnscholten

dojo/finding/deduplication.py

@@ -1098,6 +1098,13 @@ def do_false_positive_history_batch(findings):
     # Fetch all candidate existing findings with one DB query
     candidates = _fetch_fp_candidates_for_batch(findings, product, dedup_alg)
 
+    # Optional plugin hook: refine the per-finding candidate list after it is resolved by
+    # deduplication_algorithm. Lets a plugin (e.g. Pro) narrow candidates by fields that are
+    # excluded from the hash string but compared per pair (set-match tokens on
+    # vulnerability_ids / CWEs). Resolved once; a no-op when unset. See get_custom_method.
+    from dojo.utils import get_custom_method  # noqa: PLC0415 -- circular import
+    fp_candidate_filter = get_custom_method("FINDING_FALSE_POSITIVE_HISTORY_CANDIDATE_FILTER_METHOD")
+
     to_mark_as_fp_ids: set = set()
 
     for finding in findings:
@@ -1121,6 +1128,9 @@ def do_false_positive_history_batch(findings):
         else:
             existing = []
 
+        if fp_candidate_filter:
+            existing = fp_candidate_filter(finding, existing)
+
         existing_fps = [ef for ef in existing if ef.false_p]
 
         if existing_fps:

unittests/test_false_positive_history_logic.py

@@ -4,6 +4,7 @@
 
 from crum import impersonate
 from django.conf import settings
+from django.test import override_settings
 
 from dojo.finding.deduplication import do_false_positive_history_batch
 from dojo.finding.ui.views import EditFinding
@@ -125,6 +126,24 @@
 # product 3: Security Podcast
 
 
+# Module-level candidate-filter hooks for FINDING_FALSE_POSITIVE_HISTORY_CANDIDATE_FILTER_METHOD.
+# get_custom_method resolves the setting to a dotted path and imports it, so these must be
+# importable at module scope.
+_fp_candidate_filter_calls = []
+
+
+def _drop_all_fp_candidates(finding, candidates):
+    """Hook that discards every candidate — simulates a plugin rejecting all matches."""
+    _fp_candidate_filter_calls.append((finding, list(candidates)))
+    return []
+
+
+def _passthrough_fp_candidates(finding, candidates):
+    """Hook that keeps every candidate — FP history must behave exactly as with no hook."""
+    _fp_candidate_filter_calls.append((finding, list(candidates)))
+    return candidates
+
+
 @versioned_fixtures
 class TestFalsePositiveHistoryLogic(DojoTestCase):
     fixtures = ["dojo_testdata.json"]
@@ -175,6 +194,46 @@ def test_fp_history_equal_hash_code_same_test(self):
         self.assert_finding(find_created_before_mark, false_p=True, not_pk=2, test_id=3, hash_code=find_2.hash_code)
         self.assert_finding(find_created_after_mark, false_p=True, not_pk=2, test_id=3, hash_code=find_2.hash_code)
 
+    # Candidate-filter hook (FINDING_FALSE_POSITIVE_HISTORY_CANDIDATE_FILTER_METHOD) #
+
+    @override_settings(
+        FINDING_FALSE_POSITIVE_HISTORY_CANDIDATE_FILTER_METHOD="unittests.test_false_positive_history_logic._drop_all_fp_candidates",
+    )
+    def test_fp_history_hook_can_suppress_matches(self):
+        # A plugin hook that drops all candidates must prevent FP replication even when
+        # findings share a hash_code with an existing false-positive finding.
+        _fp_candidate_filter_calls.clear()
+        find_created_before_mark, find_2 = self.copy_and_reset_finding(find_id=2)
+        find_created_before_mark.save()
+        find_2 = Finding.objects.get(id=2)
+        find_2.false_p = True
+        find_2.save()
+        find_created_after_mark, find_2 = self.copy_and_reset_finding(find_id=2)
+        find_created_after_mark.save()
+        # Hook discarded every candidate, so neither copy is marked despite the shared hash_code.
+        self.assert_finding(find_created_before_mark, false_p=False, not_pk=2, test_id=3, hash_code=find_2.hash_code)
+        self.assert_finding(find_created_after_mark, false_p=False, not_pk=2, test_id=3, hash_code=find_2.hash_code)
+        # And the hook was actually invoked.
+        self.assertTrue(_fp_candidate_filter_calls)
+
+    @override_settings(
+        FINDING_FALSE_POSITIVE_HISTORY_CANDIDATE_FILTER_METHOD="unittests.test_false_positive_history_logic._passthrough_fp_candidates",
+    )
+    def test_fp_history_hook_passthrough_matches_default(self):
+        # A passthrough hook must leave default FP-history behavior unchanged.
+        _fp_candidate_filter_calls.clear()
+        find_created_before_mark, find_2 = self.copy_and_reset_finding(find_id=2)
+        find_created_before_mark.save()
+        find_2 = Finding.objects.get(id=2)
+        find_2.false_p = True
+        find_2.save()
+        find_created_after_mark, find_2 = self.copy_and_reset_finding(find_id=2)
+        find_created_after_mark.save()
+        # Identical outcome to test_fp_history_equal_hash_code_same_test — both copies marked.
+        self.assert_finding(find_created_before_mark, false_p=True, not_pk=2, test_id=3, hash_code=find_2.hash_code)
+        self.assert_finding(find_created_after_mark, false_p=True, not_pk=2, test_id=3, hash_code=find_2.hash_code)
+        self.assertTrue(_fp_candidate_filter_calls)
+
     # Finding 2 in Product 2, Engagement 1, Test 3
     def test_fp_history_equal_hash_code_same_test_non_retroactive(self):
         # Disable retroactive FP history