The following change introduced tons of reference leaks:

commit ac46eb4ad6662cf6d771b20d8963658b2186c48c
Author: Dino Viehland <dinoviehland@fb.com>
Date:   Wed Sep 11 10:16:34 2019 -0700

    bpo-38113: Update the Python-ast.c generator to PEP384 (gh-15957)
    
    Summary: This mostly migrates Python-ast.c to PEP384 and removes all statics from the whole file. This modifies the generator itself that generates the Python-ast.c. It leaves in the usage of _PyObject_LookupAttr even though it's not fully PEP384 compatible (this could always be shimmed in by anyone who needs it).


Full list of tests which leaked in build:
https://buildbot.python.org/all/#/builders/1/builds/712

test_ast
test_asyncio
test_builtin
test_capi
test_check_c_globals
test_clinic
test_compile
test_dataclasses
test_dbm
test_dbm_dumb
test_decimal
test_fstring
test_getpass
test_idle
test_importlib
test_inspect
test_pydoc
test_source_encoding
test_symtable
test_sys
test_type_comments
test_types
test_unittest


vstinner@apu$ ./python -m test -j0 -R 3:3 --fromfile=leak
(...)
test_dbm_dumb leaked [938, 896, 908] references, sum=2742
test_dbm leaked [144, 144, 144] references, sum=432
test_builtin leaked [128, 128, 128] references, sum=384
test_clinic leaked [1935, 1933, 1935] references, sum=5803
test_getpass leaked [21, 21, 21] references, sum=63
test_dataclasses leaked [8, 8, 8] references, sum=24
test_idle leaked [69, 69, 69] references, sum=207
test_inspect leaked [539, 539, 539] references, sum=1617
test_fstring leaked [104, 104, 104] references, sum=312
test_type_comments leaked [1337, 1335, 1337] references, sum=4009
test_types leaked [7, 7, 7] references, sum=21
test_compile leaked [3690, 3688, 3690] references, sum=11068
test_sys leaked [1, 1, 1] references, sum=3
test_pydoc leaked [1504, 1502, 1504] references, sum=4510
test_ast leaked [357792, 357790, 357792] references, sum=1073374
test_ast leaked [12, 11, 12] memory blocks, sum=35
test_unittest leaked [3803, 3801, 3803] references, sum=11407
test_decimal leaked [841, 841, 841] references, sum=2523
test_capi leaked [2, 2, 2] references, sum=6

I interrupted test_asyncio test: it's too slow.


Reverting the commit ac46eb4ad6662cf6d771b20d8963658b2186c48c fix most reference leaks, except of test_capi: bpo-38150.