Fix collection of direct symlinked files not in python_files

Fixes https://github.com/pytest-dev/pytest/issues/4325.

changelog/4321.bugfix.rst

@@ -0,0 +1 @@
+Fix ``item.nodeid`` with resolved symlinks.

changelog/4325.bugfix.rst

@@ -0,0 +1 @@
+Fix collection of direct symlinked files, where the target does not match ``python_files``.

src/_pytest/main.py

@@ -488,7 +488,7 @@ class Session(nodes.FSCollector):
         from _pytest.python import Package
 
         names = self._parsearg(arg)
-        argpath = names.pop(0).realpath()
+        argpath = names.pop(0)
 
         # Start with a Session root, and delve to argpath item (dir or file)
         # and stack all Packages found on the way.
@@ -636,7 +636,7 @@ class Session(nodes.FSCollector):
                     "file or package not found: " + arg + " (missing __init__.py?)"
                 )
             raise UsageError("file not found: " + arg)
-        parts[0] = path
+        parts[0] = path.realpath()
         return parts
 
     def matchnodes(self, matching, names):

testing/test_collection.py

@@ -6,6 +6,8 @@ import pprint
 import sys
 import textwrap
 
+import py
+
 import pytest
 from _pytest.main import _in_venv
 from _pytest.main import EXIT_NOTESTSCOLLECTED
@@ -1051,3 +1053,55 @@ def test_collect_handles_raising_on_dunder_class(testdir):
     result = testdir.runpytest()
     assert result.ret == 0
     result.stdout.fnmatch_lines(["*1 passed in*"])
+
+
+@pytest.mark.skipif(
+    not hasattr(py.path.local, "mksymlinkto"),
+    reason="symlink not available on this platform",
+)
+def test_collect_symlink_file_arg(testdir):
+    """Test that collecting a direct symlink, where the target does not match python_files works (#4325)."""
+    real = testdir.makepyfile(
+        real="""
+        def test_nodeid(request):
+            assert request.node.nodeid == "real.py::test_nodeid"
+        """
+    )
+    symlink = testdir.tmpdir.join("symlink.py")
+    symlink.mksymlinkto(real)
+    result = testdir.runpytest("-v", symlink)
+    result.stdout.fnmatch_lines(["real.py::test_nodeid PASSED*", "*1 passed in*"])
+    assert result.ret == 0
+
+
+@pytest.mark.skipif(
+    not hasattr(py.path.local, "mksymlinkto"),
+    reason="symlink not available on this platform",
+)
+def test_collect_symlink_out_of_tree(testdir):
+    """Test collection of symlink via out-of-tree rootdir."""
+    sub = testdir.tmpdir.join("sub")
+    real = sub.join("test_real.py")
+    real.write(
+        textwrap.dedent(
+            """
+        def test_nodeid(request):
+            # Should not contain sub/ prefix.
+            assert request.node.nodeid == "test_real.py::test_nodeid"
+        """
+        ),
+        ensure=True,
+    )
+
+    out_of_tree = testdir.tmpdir.join("out_of_tree").ensure(dir=True)
+    symlink_to_sub = out_of_tree.join("symlink_to_sub")
+    symlink_to_sub.mksymlinkto(sub)
+    sub.chdir()
+    result = testdir.runpytest("-vs", "--rootdir=%s" % sub, symlink_to_sub)
+    result.stdout.fnmatch_lines(
+        [
+            # Should not contain "sub/"!
+            "test_real.py::test_nodeid PASSED"
+        ]
+    )
+    assert result.ret == 0