Use Python's builtin warnings filters

tests/test_pyi_files.py

@@ -1,45 +1,12 @@
 import glob
 import os
-import os.path
 import re
 import subprocess
 import sys
 from itertools import zip_longest
 
 import pytest
 
-IGNORED_DEPRECATION_WARNINGS = [
-    # Ignore all DeprecationWarnings that come from pyflakes or flake8-bugbear
-    rf"{re.escape(os.path.join('pyflakes', 'checker.py'))}:\d+: DeprecationWarning: ",
-    r"bugbear\.py:\d+: DeprecationWarning: ",
-]
-IGNORED_DEPRECATION_PATTERNS = [
-    re.compile(pattern) for pattern in IGNORED_DEPRECATION_WARNINGS
-]
-
-
-def get_filtered_stderr(stderr: str) -> str:
-    lines = stderr.splitlines()
-
-    grouped_lines = []
-    skip_this_line = False
-    for line, next_line in zip_longest(lines, lines[1:]):
-        if skip_this_line:
-            skip_this_line = False
-        elif next_line is None:
-            grouped_lines.append(line)
-        elif "DeprecationWarning" in line:
-            grouped_lines.append(line + "\n" + next_line)
-            skip_this_line = True
-        else:
-            grouped_lines.append(line)
-
-    return "\n".join(
-        line
-        for line in grouped_lines
-        if not any(pattern.search(line) for pattern in IGNORED_DEPRECATION_PATTERNS)
-    )
-
 
 @pytest.mark.parametrize("path", glob.glob("tests/*.pyi"))
 def test_pyi_file(path: str) -> None:
@@ -75,27 +42,33 @@ def test_pyi_file(path: str) -> None:
         option = flag.split("=")[0]
         assert option != "--ignore", bad_flag_msg
 
+    # Silence DeprecationWarnings from our dependencies (pyflakes, flake8-bugbear, etc.)
+    #
+    # For DeprecationWarnings coming from flake8-pyi itself,
+    # print the first occurence of each warning to stderr.
+    # This will fail CI the same as `-Werror:::pyi`,
+    # but the test failure report that pyflakes gives is much easier to read
+    # if we use `-Wdefault:::pyi`
+    flake8_invocation = [
+        sys.executable,
+        "-Wignore",
+        "-Wdefault:::pyi",
+        "-m",
+        "flake8",
+        "-j0",
+    ]
+
     run_results = [
         # Passing a file on command line
         subprocess.run(
-            [sys.executable, "-Walways", "-m", "flake8", "-j0", *flags, path],
+            [*flake8_invocation, *flags, path],
             env={**os.environ, "PYTHONPATH": "."},
             capture_output=True,
             text=True,
         ),
         # Passing "-" as the file, and reading from stdin instead
         subprocess.run(
-            [
-                sys.executable,
-                "-Walways",
-                "-m",
-                "flake8",
-                "-j0",
-                "--stdin-display-name",
-                path,
-                *flags,
-                "-",
-            ],
+            [*flake8_invocation, "--stdin-display-name", path, *flags, "-"],
             env={**os.environ, "PYTHONPATH": "."},
             input=file_contents,
             capture_output=True,
@@ -104,8 +77,7 @@ def test_pyi_file(path: str) -> None:
     ]
 
     for run_result in run_results:
-        output = run_result.stdout
-        if stderr := get_filtered_stderr(run_result.stderr):
-            output += "\n" + stderr
-        output = re.sub(":[0-9]+: ", ": ", output)  # ignore column numbers
+        output = re.sub(":[0-9]+: ", ": ", run_result.stdout)  # ignore column numbers
+        if run_result.stderr:
+            output += "\n" + run_result.stderr
         assert output == expected_output