feat: two new default exclusions. #831

Author: nedbat

CHANGES.rst

@@ -23,7 +23,11 @@ upgrading your version of coverage.py.
 Unreleased
 ----------
 
-Nothing yet.
+- Two new exclusion patterns are part of the defaults: `...` is automatically
+  excluded as a line and `if TYPE_CHECKING` is excluded as a branch.  Closes
+  `issue 831`_.
+
+.. _issue 831: https://github.com/nedbat/coveragepy/issues/831
 
 
 .. start-releases

coverage/config.py

@@ -152,6 +152,7 @@ def getregexlist(self, section: str, option: str) -> list[str]:
 # The default line exclusion regexes.
 DEFAULT_EXCLUDE = [
     r"#\s*(pragma|PRAGMA)[:\s]?\s*(no|NO)\s*(cover|COVER)",
+    r"^\s*\.\.\.\s*(#|$)",
 ]
 
 # The default partial branch regexes, to be modified by the user.
@@ -165,6 +166,7 @@ def getregexlist(self, section: str, option: str) -> list[str]:
 DEFAULT_PARTIAL_ALWAYS = [
     "while (True|1|False|0):",
     "if (True|1|False|0):",
+    r"if (typing\.)?TYPE_CHECKING:",
 ]
 
 

coverage/version.py

@@ -8,7 +8,7 @@
 
 # version_info: same semantics as sys.version_info.
 # _dev: the .devN suffix if any.
-version_info = (7, 9, 3, "alpha", 0)
+version_info = (7, 10, 0, "alpha", 0)
 _dev = 1
 
 

doc/config.rst

@@ -620,7 +620,7 @@ Settings common to many kinds of reporting.
 (multi-string) A list of regular expressions.  This setting is similar to
 :ref:`config_report_exclude_lines`: it specifies patterns for lines to exclude
 from reporting.  This setting is preferred, because it will preserve the
-default exclude pattern ``pragma: no cover`` instead of overwriting it.
+default exclude patterns like ``pragma: no cover`` instead of overwriting them.
 
 See :ref:`config_report_exclude_lines` for further details.
 

doc/excluding.rst

@@ -70,14 +70,37 @@ Because the ``else`` clause is excluded, the ``if`` only has one possible next
 line, so it isn't considered a branch at all.
 
 
+Default exclusions
+------------------
+
+Coverage.py has a set of built-in exclusion patterns.  For line coverage, these
+lines are automatically excluded:
+
+- Any line with a comment like ``# pragma: no cover``.  Other slight
+  differences in spacing and letter case are also recognized.
+
+- Any line with only ``...`` in the code.
+
+For branch coverage, these kinds of branches are automatically excluded:
+
+- A branch with a comment like ``# pragma: no branch``, including differences
+  in spacing and letter case.
+
+- Some branches that are known at compile time: ``if True:``, ``while True:``,
+  and so on.
+
+- A branch just for the type checker: ``if TYPE_CHECKING:``.
+
+
 Advanced exclusion
 ------------------
 
 Coverage.py identifies exclusions by matching source code against a list of
 regular expressions. Using :ref:`configuration files <config>` or the coverage
 :ref:`API <api>`, you can add to that list. This is useful if you have
 often-used constructs to exclude that can be matched with a regex. You can
-exclude them all at once without littering your code with exclusion pragmas.
+exclude them all at once in your configuration without littering your code with
+exclusion pragmas.
 
 Before coverage.py 7.6.0, the regexes were matched against single lines of your
 source code.  Now they can be multi-line regexes that find matches across

tests/test_arcs.py

@@ -2160,9 +2160,13 @@ def test_default(self) -> None:
             e = 7
             if e:#\tpragma:\tno branch
                 f = 9
+            import typing
+            if typing.TYPE_CHECKING:    # only for mypy
+                g = 12
             """,
-            lines=[1,2,3,4,5,6,7,8,9],
-            branchz="23 24 56 57 89 8.",
+            lines=[1,2,3,4,5,6,7,8,9,10,11,12],
+            missing="12",
+            branchz="23 24 56 57 89 8A BC B.",
             branchz_missing="",
         )
 

tests/test_coverage.py

@@ -1424,8 +1424,12 @@ def test_default(self) -> None:
             e = 5
             f = 6#\tpragma:\tno cover
             g = 7
+            ...
+            i = 9
+            ...     # we don't care about this line
+            k = 11
             """,
-            lines=[1,3,5,7],
+            lines=[1,3,5,7,9,11],
         )
 
     def test_two_excludes(self) -> None:
@@ -1506,13 +1510,13 @@ def test_excluded_comprehension_branches(self) -> None:
         self.check_coverage("""\
             x, y = [0], [1]
             if x == [2]:
-                raise NotImplementedError   # pragma: NO COVER
+                raise NotImplementedError   # NOCOVPLZ
             if all(_ == __ for _, __ in zip(x, y)):
-                raise NotImplementedError   # pragma: NO COVER
+                raise NotImplementedError   # NOCOVPLZ
             """,
             lines=[1,2,4],
             missing="",
-            excludes=['#pragma: NO COVER'],
+            excludes=['# NOCOVPLZ'],
             branchz="23 24 45 4.",
             branchz_missing="",
         )