From 59e6fb94b5e47bcb8db58c7d704ff389a0b0a8a6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Stradomski?= <pstradomski@google.com>
Date: Thu, 7 Feb 2019 02:04:06 +0100
Subject: [PATCH 1/2] Fix "ValueError: Plugin already registered" exceptions
 when running in build directories that symlink to actual source.

---
 changelog/526.bugfix.rst       |  1 +
 src/_pytest/config/__init__.py |  2 +-
 testing/test_conftest.py       | 36 ++++++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 changelog/526.bugfix.rst

diff --git a/changelog/526.bugfix.rst b/changelog/526.bugfix.rst
new file mode 100644
index 000000000..022183b88
--- /dev/null
+++ b/changelog/526.bugfix.rst
@@ -0,0 +1 @@
+Fix "ValueError: Plugin already registered" exceptions when running in build directories that symlink to actual source.
diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index 26999e125..25e1d65bd 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -408,7 +408,7 @@ class PytestPluginManager(PluginManager):
                 continue
             conftestpath = parent.join("conftest.py")
             if conftestpath.isfile():
-                mod = self._importconftest(conftestpath)
+                mod = self._importconftest(conftestpath.realpath())
                 clist.append(mod)
         self._dirpath2confmods[directory] = clist
         return clist
diff --git a/testing/test_conftest.py b/testing/test_conftest.py
index 2b66d8fa7..ac091fed8 100644
--- a/testing/test_conftest.py
+++ b/testing/test_conftest.py
@@ -244,6 +244,42 @@ def test_conftest_symlink(testdir):
     assert result.ret == EXIT_OK
 
 
+@pytest.mark.skipif(
+    not hasattr(py.path.local, "mksymlinkto"),
+    reason="symlink not available on this platform",
+)
+def test_conftest_symlink_files(testdir):
+    """Check conftest.py loading when running in directory with symlinks."""
+    real = testdir.tmpdir.mkdir("real")
+    source = {
+        "app/test_foo.py": "def test1(fixture): pass",
+        "app/__init__.py": "",
+        "app/conftest.py": textwrap.dedent(
+            """
+            import pytest
+
+            print("conftest_loaded")
+
+            @pytest.fixture
+            def fixture():
+                print("fixture_used")
+            """
+        ),
+    }
+    testdir.makepyfile(**{"real/%s" % k: v for k, v in source.items()})
+
+    # Create a build directory that contains symlinks to actual files
+    # but doesn't symlink actual directories.
+    build = testdir.tmpdir.mkdir("build")
+    build.mkdir("app")
+    for f in source:
+        build.join(f).mksymlinkto(real.join(f))
+    build.chdir()
+    result = testdir.runpytest("-vs", "app/test_foo.py")
+    result.stdout.fnmatch_lines(["*conftest_loaded*", "PASSED"])
+    assert result.ret == EXIT_OK
+
+
 def test_no_conftest(testdir):
     testdir.makeconftest("assert 0")
     result = testdir.runpytest("--noconftest")

From 391dc549c05a3d262a9f7835c8cfa053f0e4e502 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Stradomski?=
 <44680433+pstradomski@users.noreply.github.com>
Date: Thu, 7 Feb 2019 12:56:13 +0100
Subject: [PATCH 2/2] Add comment on why realpath is needed

---
 src/_pytest/config/__init__.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index 25e1d65bd..3943f8472 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -408,6 +408,9 @@ class PytestPluginManager(PluginManager):
                 continue
             conftestpath = parent.join("conftest.py")
             if conftestpath.isfile():
+                # Use realpath to avoid loading the same conftest twice
+                # with build systems that create build directories containing
+                # symlinks to actual files.
                 mod = self._importconftest(conftestpath.realpath())
                 clist.append(mod)
         self._dirpath2confmods[directory] = clist