feat: add extend_exclude option

coverage/config.py

@@ -215,6 +215,7 @@ def __init__(self) -> None:
 
         # Defaults for [report]
         self.exclude_list = DEFAULT_EXCLUDE[:]
+        self.exclude_also: List[str] = []
         self.fail_under = 0.0
         self.format: Optional[str] = None
         self.ignore_errors = False
@@ -392,6 +393,7 @@ def copy(self) -> CoverageConfig:
 
         # [report]
         ('exclude_list', 'report:exclude_lines', 'regexlist'),
+        ('exclude_also', 'report:exclude_also', 'regexlist'),
         ('fail_under', 'report:fail_under', 'float'),
         ('format', 'report:format', 'boolean'),
         ('ignore_errors', 'report:ignore_errors', 'boolean'),
@@ -523,6 +525,7 @@ def post_process(self) -> None:
             (k, [self.post_process_file(f) for f in v])
             for k, v in self.paths.items()
         )
+        self.exclude_list += self.exclude_also
 
     def debug_info(self) -> List[Tuple[str, Any]]:
         """Make a list of (name, value) pairs for writing debug info."""

doc/config.rst

@@ -381,7 +381,7 @@ Settings common to many kinds of reporting.
 ......................
 
 (multi-string) A list of regular expressions.  Any line of your source code
-containing a match for  one of these regexes is excluded from being reported as
+containing a match for one of these regexes is excluded from being reported as
 missing.  More details are in :ref:`excluding`.  If you use this option, you
 are replacing all the exclude regexes, so you'll need to also supply the
 "pragma: no cover" regex if you still want to use it.
@@ -395,12 +395,22 @@ you'll exclude any line with three or more of any character. If you write
 ``pass``, you'll also exclude the line ``my_pass="foo"``, and so on.
 
 
+.. _config_report_exclude_also:
+
+[report] exclude_also
+.....................
+
+(multi-string) A list of regular expressions.  This setting will preserve the
+default exclude pattern instead of overwriting it. See
+:ref:`config_report_exclude_lines` for details on exclusion regexes.
+
+
 .. _config_report_fail_under:
 
 [report] fail_under
 ...................
 
-(float) A target coverage percentage. If the total coverage measurement is
+(float) A target coverage percentage.  If the total coverage measurement is
 under this value, then exit with a status code of 2.  If you specify a
 non-integral value, you must also set ``[report] precision`` properly to make
 use of the decimal places.  A setting of 100 will fail any value under 100,

doc/excluding.rst

@@ -101,7 +101,9 @@ For example, here's a list of exclusions I've used::
 
 Note that when using the ``exclude_lines`` option in a configuration file, you
 are taking control of the entire list of regexes, so you need to re-specify the
-default "pragma: no cover" match if you still want it to apply.
+default "pragma: no cover" match if you still want it to apply.  The
+``exclude_also`` option can be used instead to preserve the default
+exclusions while adding new ones.
 
 The regexes only have to match part of a line. Be careful not to over-match.  A
 value of ``...`` will match any line with more than three characters in it.

tests/test_config.py

@@ -449,6 +449,15 @@ def test_exceptions_from_missing_things(self) -> None:
         with pytest.raises(ConfigError, match="No option 'foo' in section: 'xyzzy'"):
             config.get("xyzzy", "foo")
 
+    def test_exclude_also(self) -> None:
+        self.make_file("pyproject.toml", """\
+            [tool.coverage.report]
+            exclude_also = ["foobar"]
+            """)
+        cov = coverage.Coverage()
+
+        assert cov.config.exclude_list == coverage.config.DEFAULT_EXCLUDE + ["foobar"]
+
 
 class ConfigFileTest(UsingModulesMixin, CoverageTest):
     """Tests of the config file settings in particular."""