pytester: add & use our own copytree instead of py.path's

Fixes the TODO note.

src/_pytest/pathlib.py

@@ -583,7 +583,7 @@ def resolve_package_path(path: Path) -> Optional[Path]:
 
 
 def visit(
-    path: str, recurse: Callable[["os.DirEntry[str]"], bool]
+    path: Union[str, "os.PathLike[str]"], recurse: Callable[["os.DirEntry[str]"], bool]
 ) -> Iterator["os.DirEntry[str]"]:
     """Walk a directory recursively, in breadth-first order.
 
@@ -657,3 +657,21 @@ def bestrelpath(directory: Path, dest: Path) -> str:
         # Forward from base to dest.
         *reldest.parts,
     )
+
+
+# Originates from py. path.local.copy(), with siginficant trims and adjustments.
+# TODO(py38): Replace with shutil.copytree(..., symlinks=True, dirs_exist_ok=True)
+def copytree(source: Path, target: Path) -> None:
+    """Recursively copy a source directory to target."""
+    assert source.is_dir()
+    for entry in visit(source, recurse=lambda entry: not entry.is_symlink()):
+        x = Path(entry)
+        relpath = x.relative_to(source)
+        newx = target / relpath
+        newx.parent.mkdir(exist_ok=True)
+        if x.is_symlink():
+            newx.symlink_to(os.readlink(x))
+        elif x.is_file():
+            shutil.copyfile(x, newx)
+        elif x.is_dir():
+            newx.mkdir(exist_ok=True)

src/_pytest/pytester.py

@@ -63,6 +63,7 @@ from _pytest.outcomes import fail
 from _pytest.outcomes import importorskip
 from _pytest.outcomes import skip
 from _pytest.pathlib import bestrelpath
+from _pytest.pathlib import copytree
 from _pytest.pathlib import make_numbered_dir
 from _pytest.reports import CollectReport
 from _pytest.reports import TestReport
@@ -935,10 +936,7 @@ class Pytester:
             example_path = example_dir.joinpath(name)
 
         if example_path.is_dir() and not example_path.joinpath("__init__.py").is_file():
-            # TODO: legacy_path.copy can copy files to existing directories,
-            # while with shutil.copytree the destination directory cannot exist,
-            # we will need to roll our own in order to drop legacy_path completely
-            legacy_path(example_path).copy(legacy_path(self.path))
+            copytree(example_path, self.path)
             return self.path
         elif example_path.is_file():
             result = self.path.joinpath(example_path.name)