Add a few missing type annotations in _pytest._code

These are more "dirty" than the previous batch (that's why they were
left out). The trouble is that `compile` can return either a code object
or an AST depending on a flag, so we need to add an overload to make the
common case Union free. But it's still worthwhile.

src/_pytest/_code/code.py

@@ -67,7 +67,7 @@ def __ne__(self, other):
         return not self == other
 
     @property
-    def path(self):
+    def path(self) -> Union[py.path.local, str]:
         """ return a path object pointing to source code (note that it
         might not point to an actually existing file). """
         try:
@@ -335,7 +335,7 @@ def cut(
                 (path is None or codepath == path)
                 and (
                     excludepath is None
-                    or not hasattr(codepath, "relto")
+                    or not isinstance(codepath, py.path.local)
                     or not codepath.relto(excludepath)
                 )
                 and (lineno is None or x.lineno == lineno)

src/_pytest/_code/source.py

@@ -6,6 +6,7 @@
 import tokenize
 import warnings
 from bisect import bisect_right
+from types import CodeType
 from types import FrameType
 from typing import Iterator
 from typing import List
@@ -17,6 +18,10 @@
 import py
 
 from _pytest.compat import overload
+from _pytest.compat import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from typing_extensions import Literal
 
 
 class Source:
@@ -120,7 +125,7 @@ def getstatement(self, lineno: int) -> "Source":
         start, end = self.getstatementrange(lineno)
         return self[start:end]
 
-    def getstatementrange(self, lineno: int):
+    def getstatementrange(self, lineno: int) -> Tuple[int, int]:
         """ return (start, end) tuple which spans the minimal
             statement region which containing the given lineno.
         """
@@ -158,14 +163,36 @@ def isparseable(self, deindent: bool = True) -> bool:
     def __str__(self) -> str:
         return "\n".join(self.lines)
 
+    @overload
     def compile(
         self,
-        filename=None,
-        mode="exec",
+        filename: Optional[str] = ...,
+        mode: str = ...,
+        flag: "Literal[0]" = ...,
+        dont_inherit: int = ...,
+        _genframe: Optional[FrameType] = ...,
+    ) -> CodeType:
+        raise NotImplementedError()
+
+    @overload  # noqa: F811
+    def compile(  # noqa: F811
+        self,
+        filename: Optional[str] = ...,
+        mode: str = ...,
+        flag: int = ...,
+        dont_inherit: int = ...,
+        _genframe: Optional[FrameType] = ...,
+    ) -> Union[CodeType, ast.AST]:
+        raise NotImplementedError()
+
+    def compile(  # noqa: F811
+        self,
+        filename: Optional[str] = None,
+        mode: str = "exec",
         flag: int = 0,
         dont_inherit: int = 0,
         _genframe: Optional[FrameType] = None,
-    ):
+    ) -> Union[CodeType, ast.AST]:
         """ return compiled code object. if filename is None
             invent an artificial filename which displays
             the source/line position of the caller frame.
@@ -196,7 +223,9 @@ def compile(
             raise newex
         else:
             if flag & ast.PyCF_ONLY_AST:
+                assert isinstance(co, ast.AST)
                 return co
+            assert isinstance(co, CodeType)
             lines = [(x + "\n") for x in self.lines]
             # Type ignored because linecache.cache is private.
             linecache.cache[filename] = (1, None, lines, filename)  # type: ignore
@@ -208,22 +237,52 @@ def compile(
 #
 
 
-def compile_(source, filename=None, mode="exec", flags: int = 0, dont_inherit: int = 0):
+@overload
+def compile_(
+    source: Union[str, bytes, ast.mod, ast.AST],
+    filename: Optional[str] = ...,
+    mode: str = ...,
+    flags: "Literal[0]" = ...,
+    dont_inherit: int = ...,
+) -> CodeType:
+    raise NotImplementedError()
+
+
+@overload  # noqa: F811
+def compile_(  # noqa: F811
+    source: Union[str, bytes, ast.mod, ast.AST],
+    filename: Optional[str] = ...,
+    mode: str = ...,
+    flags: int = ...,
+    dont_inherit: int = ...,
+) -> Union[CodeType, ast.AST]:
+    raise NotImplementedError()
+
+
+def compile_(  # noqa: F811
+    source: Union[str, bytes, ast.mod, ast.AST],
+    filename: Optional[str] = None,
+    mode: str = "exec",
+    flags: int = 0,
+    dont_inherit: int = 0,
+) -> Union[CodeType, ast.AST]:
     """ compile the given source to a raw code object,
         and maintain an internal cache which allows later
         retrieval of the source code for the code object
         and any recursively created code objects.
     """
     if isinstance(source, ast.AST):
         # XXX should Source support having AST?
-        return compile(source, filename, mode, flags, dont_inherit)
+        assert filename is not None
+        co = compile(source, filename, mode, flags, dont_inherit)
+        assert isinstance(co, (CodeType, ast.AST))
+        return co
     _genframe = sys._getframe(1)  # the caller
     s = Source(source)
-    co = s.compile(filename, mode, flags, _genframe=_genframe)
-    return co
+    return s.compile(filename, mode, flags, _genframe=_genframe)
 
 
-def getfslineno(obj):
+def getfslineno(obj) -> Tuple[Union[str, py.path.local], int]:
     """ Return source location (path, lineno) for the given object.
     If the source cannot be determined return ("", -1).
 

testing/code/test_source.py

@@ -4,10 +4,13 @@
 import ast
 import inspect
 import sys
+from types import CodeType
 from typing import Any
 from typing import Dict
 from typing import Optional
 
+import py
+
 import _pytest._code
 import pytest
 from _pytest._code import Source
@@ -147,6 +150,10 @@ def test_getrange(self) -> None:
         assert len(x.lines) == 2
         assert str(x) == "def f(x):\n    pass"
 
+    def test_getrange_step_not_supported(self) -> None:
+        with pytest.raises(IndexError, match=r"step"):
+            self.source[::2]
+
     def test_getline(self) -> None:
         x = self.source[0]
         assert x == "def f(x):"
@@ -449,6 +456,14 @@ def test_idem_compile_and_getsource() -> None:
     assert src == expected
 
 
+def test_compile_ast() -> None:
+    # We don't necessarily want to support this.
+    # This test was added just for coverage.
+    stmt = ast.parse("def x(): pass")
+    co = _pytest._code.compile(stmt, filename="foo.py")
+    assert isinstance(co, CodeType)
+
+
 def test_findsource_fallback() -> None:
     from _pytest._code.source import findsource
 
@@ -488,6 +503,7 @@ def f(x) -> None:
 
     fspath, lineno = getfslineno(f)
 
+    assert isinstance(fspath, py.path.local)
     assert fspath.basename == "test_source.py"
     assert lineno == f.__code__.co_firstlineno - 1  # see findsource