De-duplicate warnings metadata in the report JSON

This was causing the report file sizes to be huge, especially for plain numpy.

Author: asmeurer

conftest.py

@@ -7,7 +7,7 @@
 from array_api_tests import _array_module as xp
 from array_api_tests._array_module import _UndefinedStub
 
-from reporting import pytest_metadata, add_extra_json_metadata # noqa
+from reporting import pytest_metadata, pytest_json_modifyreport, add_extra_json_metadata # noqa
 
 settings.register_profile("xp_default", deadline=800)
 

reporting.py

@@ -2,6 +2,7 @@
 from array_api_tests import _array_module as xp
 from array_api_tests import __version__
 
+from collections import Counter
 from types import BuiltinFunctionType, FunctionType
 import dataclasses
 import json
@@ -89,3 +90,19 @@ def finalizer():
             add_metadata('hypothesis_statistics', request.node.hypothesis_statistics)
 
     request.addfinalizer(finalizer)
+
+def pytest_json_modifyreport(json_report):
+    # Deduplicate warnings. These duplicate warnings can cause the file size
+    # to become huge. For instance, a warning from np.bool which is emitted
+    # every time hypothesis runs (over a million times) causes the warnings
+    # JSON for a plain numpy namespace run to be over 500MB.
+
+    # This will lose information about what order the warnings were issued in,
+    # but that isn't particularly helpful anyway since the warning metadata
+    # doesn't store a full stack of where it was issued from. The resulting
+    # warnings will be in order of the first time each warning is issued since
+    # collections.Counter is ordered just like dict().
+    counted_warnings = Counter([frozenset(i.items()) for i in json_report['warnings']])
+    deduped_warnings = [{**dict(i), 'count': counted_warnings[i]} for i in counted_warnings]
+
+    json_report['warnings'] = deduped_warnings