From c2179c31279cc9fd78138f4714edaadb1421b5e8 Mon Sep 17 00:00:00 2001
From: Jeffrey Rackauckas <jeffreyrack@gmail.com>
Date: Sun, 30 Sep 2018 18:34:56 -0700
Subject: [PATCH 1/2] Improve error messaging when invalid syntax is passed to
 the -m option

---
 changelog/4051.trivial     |  1 +
 src/_pytest/mark/legacy.py |  5 ++++-
 testing/test_mark.py       | 12 ++++++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 changelog/4051.trivial

diff --git a/changelog/4051.trivial b/changelog/4051.trivial
new file mode 100644
index 000000000..401f3b1a8
--- /dev/null
+++ b/changelog/4051.trivial
@@ -0,0 +1 @@
+Imrpove Error messaging when Invalid Python Syntax is passed through the ``-m`` option to limit what marks to run against.
diff --git a/src/_pytest/mark/legacy.py b/src/_pytest/mark/legacy.py
index ab016a035..0d0d852ce 100644
--- a/src/_pytest/mark/legacy.py
+++ b/src/_pytest/mark/legacy.py
@@ -66,7 +66,10 @@ python_keywords_allowed_list = ["or", "and", "not"]
 
 def matchmark(colitem, markexpr):
     """Tries to match on any marker names, attached to the given colitem."""
-    return eval(markexpr, {}, MarkMapping.from_item(colitem))
+    try:
+        return eval(markexpr, {}, MarkMapping.from_item(colitem))
+    except SyntaxError as e:
+        raise SyntaxError(str(e) + "\nMarker expression must be valid Python!")
 
 
 def matchkeyword(colitem, keywordexpr):
diff --git a/testing/test_mark.py b/testing/test_mark.py
index ddeff2789..06bbe65f4 100644
--- a/testing/test_mark.py
+++ b/testing/test_mark.py
@@ -786,6 +786,18 @@ class TestFunctional(object):
         deselected_tests = dlist[0].items
         assert len(deselected_tests) == 2
 
+    def test_invalid_m_option(self, testdir):
+        testdir.makepyfile(
+            """
+            def test_a():
+                pass
+        """
+        )
+        result = testdir.runpytest("-m bogus/")
+        result.stdout.fnmatch_lines(
+            ["INTERNALERROR> Marker expression must be valid Python!"]
+        )
+
     def test_keywords_at_node_level(self, testdir):
         testdir.makepyfile(
             """

From 7a6d16c1eb6b374386138a5e7f8017ef7ce2ff86 Mon Sep 17 00:00:00 2001
From: Jeffrey Rackauckas <jeffreyrack@gmail.com>
Date: Sun, 30 Sep 2018 18:45:49 -0700
Subject: [PATCH 2/2] Adding .rst to end of changelog fragment filename.

---
 changelog/{4051.trivial => 4051.trivial.rst} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename changelog/{4051.trivial => 4051.trivial.rst} (100%)

diff --git a/changelog/4051.trivial b/changelog/4051.trivial.rst
similarity index 100%
rename from changelog/4051.trivial
rename to changelog/4051.trivial.rst