From 9b0c33d15d204f80a44ef64da41bc572ba753761 Mon Sep 17 00:00:00 2001
From: Aiden Grossman <aidengrossman@google.com>
Date: Fri, 31 Oct 2025 17:01:56 -0700
Subject: [PATCH 1/2] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20ch?=
 =?UTF-8?q?anges=20to=20main=20this=20commit=20is=20based=20on?=
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Created using spr 1.3.7

[skip ci]
---
 premerge/advisor/advisor_lib.py      | 39 +++++++++++++++++++++++++---
 premerge/advisor/advisor_lib_test.py |  9 +++++++
 2 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/premerge/advisor/advisor_lib.py b/premerge/advisor/advisor_lib.py
index 3348928f6..8b0b4a2cf 100644
--- a/premerge/advisor/advisor_lib.py
+++ b/premerge/advisor/advisor_lib.py
@@ -36,6 +36,7 @@ class TestExplanationRequest[TypedDict]:
 }
 
 EXPLAINED_HEAD_MAX_COMMIT_INDEX_DIFFERENCE = 5
+EXPLAINED_FLAKY_MIN_COMMIT_RANGE = 200
 
 
 def _create_table(table_name: str, connection: sqlite3.Connection):
@@ -131,6 +132,29 @@ def _try_explain_failing_at_head(
     return None
 
 
+def _try_explain_flaky_failure(
+    db_connection: sqlite3.Connection,
+    test_failure: TestFailure,
+    platform: str,
+) -> FailureExplanation | None:
+    test_name_matches = db_connection.execute(
+        "SELECT failure_message, commit_index FROM failures WHERE source_type='postcommit' AND platform=?",
+        (platform,),
+    ).fetchall()
+    commit_indices = []
+    for failure_message, commit_index in test_name_matches:
+        if failure_message == test_failure.message:
+            commit_indices.append(commit_index)
+    commit_range = max(commit_indices) - min(commit_indices)
+    if commit_range > EXPLAINED_FLAKY_MIN_COMMIT_RANGE:
+        return {
+            "name": test_failure["name"],
+            "explained": True,
+            "reason": "This test is flaky in main.",
+        }
+    return None
+
+
 def explain_failures(
     explanation_request: TestExplanationRequest,
     repository_path: str,
@@ -138,18 +162,27 @@ def explain_failures(
 ) -> list[FailureExplanation]:
     explanations = []
     for test_failure in explanation_request["failures"]:
+        commit_index = git_utils.get_commit_index(
+            explanation_request["base_commit_sha"], repository_path, db_connection
+        )
         explained_at_head = _try_explain_failing_at_head(
             db_connection,
             test_failure,
             explanation_request["base_commit_sha"],
-            git_utils.get_commit_index(
-                explanation_request["base_commit_sha"], repository_path, db_connection
-            ),
+            commit_index,
             explanation_request["platform"],
         )
         if explained_at_head:
             explanations.append(explained_at_head)
             continue
+        explained_as_flaky = _try_explain_flaky_failure(
+            db_connection,
+            test_failure,
+            explanation_request["platform"],
+        )
+        if explained_as_flaky:
+            explanations.append(explained_as_flaky)
+            continue
         explanations.append(
             {"name": test_failure["name"], "explained": False, "reason": None}
         )
diff --git a/premerge/advisor/advisor_lib_test.py b/premerge/advisor/advisor_lib_test.py
index ebbfe59b5..71cc0bc63 100644
--- a/premerge/advisor/advisor_lib_test.py
+++ b/premerge/advisor/advisor_lib_test.py
@@ -280,3 +280,12 @@ def test_no_explain_different_message(self):
                 }
             ],
         )
+
+    def test_explain_flaky(self):
+        pass
+
+    def test_no_explain_flaky_pullrequest_data(self):
+        pass
+
+    def test_no_explain_flaky_long_subsequence(self):
+        pass

From eb6b6d8c0cc8ccfd498ecd294850248ab24ecfb1 Mon Sep 17 00:00:00 2001
From: Aiden Grossman <aidengrossman@google.com>
Date: Mon, 10 Nov 2025 16:48:22 -0800
Subject: [PATCH 2/2] Add comment

Created using spr 1.3.7
---
 premerge/advisor/advisor_lib.py | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/premerge/advisor/advisor_lib.py b/premerge/advisor/advisor_lib.py
index 3d21ea167..520496abc 100644
--- a/premerge/advisor/advisor_lib.py
+++ b/premerge/advisor/advisor_lib.py
@@ -137,6 +137,25 @@ def _try_explain_flaky_failure(
     test_failure: TestFailure,
     platform: str,
 ) -> FailureExplanation | None:
+    """See if a failure is flaky at head.
+
+    This function looks at a test failure and tries to see if the failure is
+    a known flake at head. It does this heuristically, by seeing if there have
+    been at least two failures across more than 200 commits. This has the
+    advantage of being a simple heuristic and performant. We do not
+    explicitly handle the case where a test has been failing continiously
+    for this amount of time as this is an OOM more range than any non-flaky
+    tests have stayed in tree.
+
+    Args:
+      db_connection: The database connection.
+      test_failure: The test failure to try and explain.
+      platform: The platform the test failed on.
+    
+    Returns:
+      Either None, if the test could not be explained as flaky, or a
+      FailureExplanation object explaining the test failure.
+    """
     test_name_matches = db_connection.execute(
         "SELECT failure_message, commit_index FROM failures WHERE source_type='postcommit' AND platform=?",
         (platform,),