fix(ci): make pyrefly diff comments focus on diagnostics (#32778)

.github/workflows/pyrefly-diff.yml

@@ -29,16 +29,22 @@ jobs:
       - name: Install dependencies
         run: uv sync --project api --dev
 
+      - name: Prepare diagnostics extractor
+        run: |
+          git show ${{ github.event.pull_request.head.sha }}:api/libs/pyrefly_diagnostics.py > /tmp/pyrefly_diagnostics.py
+
       - name: Run pyrefly on PR branch
         run: |
-          uv run --directory api pyrefly check > /tmp/pyrefly_pr.txt 2>&1 || true
+          uv run --directory api --dev pyrefly check 2>&1 \
+            | uv run --directory api python /tmp/pyrefly_diagnostics.py > /tmp/pyrefly_pr.txt || true
 
       - name: Checkout base branch
         run: git checkout ${{ github.base_ref }}
 
       - name: Run pyrefly on base branch
         run: |
-          uv run --directory api pyrefly check > /tmp/pyrefly_base.txt 2>&1 || true
+          uv run --directory api --dev pyrefly check 2>&1 \
+            | uv run --directory api python /tmp/pyrefly_diagnostics.py > /tmp/pyrefly_base.txt || true
 
       - name: Compute diff
         run: |

api/libs/pyrefly_diagnostics.py

@@ -0,0 +1,48 @@
+"""Helpers for producing concise pyrefly diagnostics for CI diff output."""
+
+from __future__ import annotations
+
+import sys
+
+_DIAGNOSTIC_PREFIXES = ("ERROR ", "WARNING ")
+_LOCATION_PREFIX = "-->"
+
+
+def extract_diagnostics(raw_output: str) -> str:
+    """Extract stable diagnostic lines from pyrefly output.
+
+    The full pyrefly output includes code excerpts and carets, which create noisy
+    diffs. This helper keeps only:
+    - diagnostic headline lines (``ERROR ...`` / ``WARNING ...``)
+    - the following location line (``--> path:line:column``), when present
+    """
+
+    lines = raw_output.splitlines()
+    diagnostics: list[str] = []
+
+    for index, line in enumerate(lines):
+        if line.startswith(_DIAGNOSTIC_PREFIXES):
+            diagnostics.append(line.rstrip())
+
+            next_index = index + 1
+            if next_index < len(lines):
+                next_line = lines[next_index]
+                if next_line.lstrip().startswith(_LOCATION_PREFIX):
+                    diagnostics.append(next_line.rstrip())
+
+    if not diagnostics:
+        return ""
+
+    return "\n".join(diagnostics) + "\n"
+
+
+def main() -> int:
+    """Read pyrefly output from stdin and print normalized diagnostics."""
+
+    raw_output = sys.stdin.read()
+    sys.stdout.write(extract_diagnostics(raw_output))
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())

api/tests/unit_tests/libs/test_pyrefly_diagnostics.py

@@ -0,0 +1,51 @@
+from libs.pyrefly_diagnostics import extract_diagnostics
+
+
+def test_extract_diagnostics_keeps_only_summary_and_location_lines() -> None:
+    # Arrange
+    raw_output = """INFO Checking project configured at `/tmp/project/pyrefly.toml`
+ERROR `result` may be uninitialized [unbound-name]
+   --> controllers/console/app/annotation.py:126:16
+    |
+126 |         return result, 200
+    |                ^^^^^^
+    |
+ERROR Object of class `App` has no attribute `access_mode` [missing-attribute]
+   --> controllers/console/app/app.py:574:13
+    |
+574 |             app_model.access_mode = app_setting.access_mode
+    |             ^^^^^^^^^^^^^^^^^^^^^
+"""
+
+    # Act
+    diagnostics = extract_diagnostics(raw_output)
+
+    # Assert
+    assert diagnostics == (
+        "ERROR `result` may be uninitialized [unbound-name]\n"
+        "   --> controllers/console/app/annotation.py:126:16\n"
+        "ERROR Object of class `App` has no attribute `access_mode` [missing-attribute]\n"
+        "   --> controllers/console/app/app.py:574:13\n"
+    )
+
+
+def test_extract_diagnostics_handles_error_without_location_line() -> None:
+    # Arrange
+    raw_output = "ERROR unexpected pyrefly output format [bad-format]\n"
+
+    # Act
+    diagnostics = extract_diagnostics(raw_output)
+
+    # Assert
+    assert diagnostics == "ERROR unexpected pyrefly output format [bad-format]\n"
+
+
+def test_extract_diagnostics_returns_empty_for_non_error_output() -> None:
+    # Arrange
+    raw_output = "INFO Checking project configured at `/tmp/project/pyrefly.toml`\n"
+
+    # Act
+    diagnostics = extract_diagnostics(raw_output)
+
+    # Assert
+    assert diagnostics == ""