Avoid exceptions post syntax errors

Fixes: #1012

examples/playbooks/syntax-error.yml

@@ -0,0 +1,6 @@
+---
+- name: This should raise syntax-error
+  hosts: localhost
+  tasks:
+    debug:
+      msg: "Note that `tasks` is not entered as a list."

src/ansiblelint/runner.py

@@ -110,9 +110,13 @@ def worker(lintable: Lintable) -> List[MatchError]:
         for data in return_list:
             matches.extend(data)
 
-        matches.extend(self._emit_matches(files))
         # -- phase 2 ---
-        if not matches:  # do our processing only when ansible syntax check passed
+        if not matches:
+
+            # do our processing only when ansible syntax check passed in order
+            # to avoid causing runtime exceptions. Our processing is not as
+            # relisient to be able process garbage.
+            matches.extend(self._emit_matches(files))
 
             # remove duplicates from files list
             files = [value for n, value in enumerate(files) if value not in files[:n]]

test/TestExamples.py

@@ -1,4 +1,6 @@
 """Assure samples produced desire outcomes."""
+import pytest
+
 from ansiblelint.runner import Runner
 
 
@@ -10,11 +12,18 @@ def test_example(default_rules_collection):
     assert len(result) == 15
 
 
-def test_example_plain_string(default_rules_collection):
+@pytest.mark.parametrize(
+    "filename",
+    (
+        pytest.param(
+            'examples/playbooks/syntax-error-string.yml', id='syntax-error-string'
+        ),
+        pytest.param('examples/playbooks/syntax-error.yml', id='syntax-error'),
+    ),
+)
+def test_example_syntax_error(default_rules_collection, filename):
     """Validates that loading valid YAML string produce error."""
-    result = Runner(
-        'examples/playbooks/plain_string.yml', rules=default_rules_collection
-    ).run()
+    result = Runner(filename, rules=default_rules_collection).run()
     assert len(result) >= 1
     passed = False
     for match in result: