[3.5] bpo-30523, bpo-30764, bpo-30776: Sync regrtest from master (#2442)

* bpo-30523: regrtest --list-cases --match (#2401)

* regrtest --list-cases now supports --match and --match-file options.
  Example: ./python -m test --list-cases -m FileTests test_os
* --list-cases now also sets support.verbose to False to prevent
  messages to stdout when loading test modules.
* Add support._match_test() private function.
(cherry picked from commit ace56d583664f855d89d1219ece7c21c2fddcf30)

* bpo-30764: regrtest: add --fail-env-changed option (#2402)

* bpo-30764: regrtest: change exit code on failure

* Exit code 2 if failed tests ("bad")
* Exit code 3 if interrupted

* bpo-30764: regrtest: add --fail-env-changed option

If the option is set, mark a test as failed if it alters the
environment, for example if it creates a file without removing it.

(cherry picked from commit 63f54c68936d648c70ca411661e4208329edcf26)

* bpo-30776: reduce regrtest -R false positives (#2422)

* Change the regrtest --huntrleaks checker to decide if a test file
  leaks or not. Require that each run leaks at least 1 reference.
* Warmup runs are now completely ignored: ignored in the checker test
  and not used anymore to compute the sum.
* Add an unit test for a reference leak.

Example of reference differences previously considered a failure
(leak) and now considered as success (success, no leak):

    [3, 0, 0]
    [0, 1, 0]
    [8, -8, 1]
(cherry picked from commit 48b5c422ffb03affb00c184b9a99e5537be92732)

1 files changed, 35 insertions, 5 deletions

diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index 299416c..339beb1 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -343,6 +343,9 @@ def _create_parser():
                             ' , don\'t execute them')
     group.add_argument('-P', '--pgo', dest='pgo', action='store_true',
                        help='enable Profile Guided Optimization training')
+    group.add_argument('--fail-env-changed', action='store_true',
+                       help='if a test file alters the environment, mark '
+                            'the test as failed')
 
     return parser
 
@@ -944,11 +947,19 @@ def main(tests=None, **kwargs):
         result = "FAILURE"
     elif interrupted:
         result = "INTERRUPTED"
+    elif environment_changed and ns.fail_env_changed:
+        result = "ENV CHANGED"
     else:
         result = "SUCCESS"
     print("Tests result: %s" % result)
 
-    sys.exit(len(bad) > 0 or interrupted)
+    if bad:
+        sys.exit(2)
+    if interrupted:
+        sys.exit(130)
+    if ns.fail_env_changed and environment_changed:
+        sys.exit(3)
+    sys.exit(0)
 
 
 # small set of tests to determine if we have a basically functioning interpreter
@@ -1510,9 +1521,21 @@ def dash_R(the_module, test, indirect_test, huntrleaks):
             alloc_deltas[i] = alloc_after - alloc_before
         alloc_before, rc_before = alloc_after, rc_after
     print(file=sys.stderr)
+
     # These checkers return False on success, True on failure
     def check_rc_deltas(deltas):
-        return any(deltas)
+        # bpo-30776: Try to ignore false positives:
+        #
+        #   [3, 0, 0]
+        #   [0, 1, 0]
+        #   [8, -8, 1]
+        #
+        # Expected leaks:
+        #
+        #   [5, 5, 6]
+        #   [10, 1, 1]
+        return all(delta >= 1 for delta in deltas)
+
     def check_alloc_deltas(deltas):
         # At least 1/3rd of 0s
         if 3 * deltas.count(0) < len(deltas):
@@ -1524,10 +1547,13 @@ def dash_R(the_module, test, indirect_test, huntrleaks):
     failed = False
     for deltas, item_name, checker in [
         (rc_deltas, 'references', check_rc_deltas),
-        (alloc_deltas, 'memory blocks', check_alloc_deltas)]:
+        (alloc_deltas, 'memory blocks', check_alloc_deltas)
+    ]:
+        # ignore warmup runs
+        deltas = deltas[nwarmup:]
         if checker(deltas):
             msg = '%s leaked %s %s, sum=%s' % (
-                test, deltas[nwarmup:], item_name, sum(deltas))
+                test, deltas, item_name, sum(deltas))
             print(msg, file=sys.stderr)
             sys.stderr.flush()
             with open(fname, "a") as refrep:
@@ -1735,10 +1761,14 @@ def _list_cases(suite):
         if isinstance(test, unittest.TestSuite):
             _list_cases(test)
         elif isinstance(test, unittest.TestCase):
-            print(test.id())
+            if support._match_test(test):
+                print(test.id())
 
 
 def list_cases(ns, selected):
+    support.verbose = False
+    support.match_tests = ns.match_tests
+
     skipped = []
     for test in selected:
         abstest = get_abs_module(ns, test)