[3.6] bpo-30523, bpo-30764, bpo-30776: Sync regrtest from master (#2441)

* 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, 14 insertions, 2 deletions

diff --git a/Lib/test/libregrtest/main.py b/Lib/test/libregrtest/main.py
index 527de17779..571eb61125 100644
--- a/Lib/test/libregrtest/main.py
+++ b/Lib/test/libregrtest/main.py
@@ -256,9 +256,13 @@ class Regrtest:
             if isinstance(test, unittest.TestSuite):
                 self._list_cases(test)
             elif isinstance(test, unittest.TestCase):
-                print(test.id())
+                if support._match_test(test):
+                    print(test.id())
 
     def list_cases(self):
+        support.verbose = False
+        support.match_tests = self.ns.match_tests
+
         for test in self.selected:
             abstest = get_abs_module(self.ns, test)
             try:
@@ -474,6 +478,8 @@ class Regrtest:
             result = "FAILURE"
         elif self.interrupted:
             result = "INTERRUPTED"
+        elif self.environment_changed and self.ns.fail_env_changed:
+            result = "ENV CHANGED"
         else:
             result = "SUCCESS"
         print("Tests result: %s" % result)
@@ -534,7 +540,13 @@ class Regrtest:
             self.rerun_failed_tests()
 
         self.finalize()
-        sys.exit(len(self.bad) > 0 or self.interrupted)
+        if self.bad:
+            sys.exit(2)
+        if self.interrupted:
+            sys.exit(130)
+        if self.ns.fail_env_changed and self.environment_changed:
+            sys.exit(3)
+        sys.exit(0)
 
 
 def removepy(names):