Session._collectfile: use realpath

This fixes runnings `pytest tests`, where `tests` is a symlink to
`project/app/tests`: previously `project/app/conftest.py` would be
ignored for fixtures then.

src/_pytest/main.py

@@ -546,6 +546,7 @@ def _collect(self, arg):
                 yield y
 
     def _collectfile(self, path):
+        path = path.realpath()
         ihook = self.gethookproxy(path)
         if not self.isinitpath(path):
             if ihook.pytest_ignore_collect(path=path, config=self.config):

testing/test_conftest.py

@@ -4,7 +4,7 @@
 import py
 import pytest
 from _pytest.config import PytestPluginManager
-from _pytest.main import EXIT_NOTESTSCOLLECTED, EXIT_USAGEERROR
+from _pytest.main import EXIT_NOTESTSCOLLECTED, EXIT_OK, EXIT_USAGEERROR
 
 
 @pytest.fixture(scope="module", params=["global", "inpackage"])
@@ -186,6 +186,41 @@ def pytest_addoption(parser):
     assert "warning: could not load initial" not in result.stdout.str()
 
 
+@pytest.mark.skipif(
+    not hasattr(py.path.local, "mksymlinkto"),
+    reason="symlink not available on this platform",
+)
+def test_conftest_symlink(testdir):
+    """Ensure that conftest.py is used for resolved symlinks."""
+    realtemp = testdir.tmpdir.mkdir("real")
+    realtests = realtemp.mkdir("tests")
+    linktemp = testdir.tmpdir.join("symlinktests")
+    linktemp.mksymlinkto(realtests)
+    testdir.makepyfile(
+        **{
+            "real/tests/test_foo.py": "def test1(fixture): pass",
+            "real/conftest.py": textwrap.dedent(
+                """
+                import pytest
+
+                print("conftest_loaded")
+
+                @pytest.fixture
+                def fixture():
+                    print("fixture_used")
+                """
+            ),
+        }
+    )
+    result = testdir.runpytest("-vs", "symlinktests")
+    result.stdout.fnmatch_lines([
+        "*conftest_loaded*",
+        "real/tests/test_foo.py::test1 fixture_used",
+        "PASSED",
+    ])
+    assert result.ret == EXIT_OK
+
+
 def test_no_conftest(testdir):
     testdir.makeconftest("assert 0")
     result = testdir.runpytest("--noconftest")