Fix collection of direct symlinked files

Fixes #4325.

Author: blueyed

changelog/4325.bugfix.rst

@@ -0,0 +1 @@
+Fix collection of direct symlinked files.

src/_pytest/main.py

@@ -488,7 +488,7 @@ def _collect(self, arg):
         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 @@ def _parsearg(self, arg):
                     "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 sys
 import textwrap
 
+import py
+
 import pytest
 from _pytest.main import _in_venv
 from _pytest.main import EXIT_NOTESTSCOLLECTED
@@ -1051,3 +1053,16 @@ def test_1():
     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 works (#4325)."""
+    p = testdir.makepyfile("def test_1(): pass")
+    testdir.tmpdir.join("symlink.py").mksymlinkto(p)
+    result = testdir.runpytest("--collect-only", "symlink.py")
+    result.stdout.fnmatch_lines(["collected 1 item"])
+    assert result.ret == 0