Fixes 4893 - error handling for malformed configurations

news/4893.bugfix

@@ -0,0 +1 @@
+Malformed configuration files now show helpful error messages, instead of tracebacks.

src/pip/_internal/configuration.py

@@ -292,6 +292,20 @@ def _construct_parser(self, fname):
                     "Configuration file contains invalid %s characters.\n"
                     "Please fix your configuration, located at %s\n"
                 ) % (locale.getpreferredencoding(False), fname))
+            except configparser.MissingSectionHeaderError as e:
+                raise ConfigurationError((
+                    "ERROR: "
+                    "Configuration file headers cannot be parsed. \n"
+                    "Please fix the section formatting of the "
+                    "configuration located at line %s of file %s\n"
+                ) % (e.lineno, fname))
+            except configparser.ParsingError as e:
+                raise ConfigurationError(
+                    "ERROR: "
+                    "Configuration file cannot be parsed. \n"
+                    "%s\n" % str(e)
+                )
+
         return parser
 
     def _load_environment_vars(self):

tests/unit/test_configuration.py

@@ -68,6 +68,21 @@ def test_environment_var_does_not_load_version(self):
         with pytest.raises(ConfigurationError):
             self.configuration.get_value(":env:.version")
 
+    def test_environment_config_errors_if_malformed(self):
+        contents = """
+            test]
+            hello = 4
+        """
+        with self.tmpfile(contents) as config_file:
+            os.environ["PIP_CONFIG_FILE"] = config_file
+
+            with pytest.raises(ConfigurationError) as err:
+                self.configuration.load()
+
+        assert "malformed" in str(err)
+        assert lineno in str(err)
+        assert filepath in str(err)
+
 
 class TestConfigurationPrecedence(ConfigurationMixin):
     # Tests for methods to that determine the order of precedence of