1 files changed, 85 insertions, 3 deletions

diff --git a/src/mailman/testing/flake8.py b/src/mailman/testing/flake8.py
index d002e8b6c..df4e39c90 100644
--- a/src/mailman/testing/flake8.py
+++ b/src/mailman/testing/flake8.py
@@ -19,17 +19,39 @@
 
 
 from ast import NodeVisitor
+from collections import namedtuple
+from enum import Enum
+
+
+class ImportType(Enum):
+    non_from = 0
+    from_import = 1
+
+
+ImportRecord = namedtuple('ImportRecord', 'itype lineno colno, module, names')
 
 
 class ImportVisitor(NodeVisitor):
     def __init__(self):
-        self.last_import = None
+        self.imports = []
 
     def visit_Import(self, node):
         if node.col_offset != 0:
             # Ignore nested imports.
             return
-        
+        names = [alias.name for alias in node.names]
+        self.imports.append(
+            ImportRecord(ImportType.non_from, node.lineno, node.col_offset,
+                         None, names))
+
+    def visit_ImportFrom(self, node):
+        if node.col_offset != 0:
+            # Ignore nested imports.
+            return
+        names = [alias.name for alias in node.names]
+        self.imports.append(
+            ImportRecord(ImportType.from_import, node.lineno, node.col_offset,
+                         node.module, names))
 
 
 class ImportOrder:
@@ -40,5 +62,65 @@ class ImportOrder:
         self.tree = tree
         self.filename = filename
 
+    def _error(self, record, code, text):
+        return (record.lineno, record.colno,
+                '{} {}'.format(code, text), ImportOrder)
+
     def run(self):
-        print('Running', self.name, self.version)
+        visitor = ImportVisitor()
+        visitor.visit(self.tree)
+        last_import = None
+        for record in visitor.imports:
+            if last_import is None:
+                last_import = record
+                continue
+            if record.itype is ImportType.non_from:
+                if len(record.names) != 1:
+                    yield self._error(record, 'B402',
+                                      'Multiple names on non-from import')
+                if last_import.itype is ImportType.from_import:
+                    yield self._error(record, 'B401',
+                                      'Non-from import follows from-import')
+                if len(last_import.names[0]) > len(record.names[0]):
+                    yield self._error(
+                        record, 'B403',
+                        'Shorter non-from import follows longer')
+                # It's also possible that the imports are the same length, in
+                # which case they must be sorted alphabetically.
+                if (len(last_import.names[0]) == len(record.names[0]) and
+                        last_import.names[0] > record.names[0]):
+                    yield self._error(
+                        record, 'B404',
+                        'Non-from imports not alphabetically sorted')
+                if last_import.lineno + 1 != record.lineno:
+                    yield self._error(
+                        record, 'B405',
+                        'Unexpected blank line since last non-from import')
+            else:
+                assert record.itype is ImportType.from_import
+                if (last_import.itype is ImportType.non_from and
+                        record.lineno != last_import.lineno + 2):
+                    yield self._error(
+                        record, 'B406',
+                        'Expected one blank line since last non-from import')
+                if last_import.itype is ImportType.non_from:
+                    last_import = record
+                    continue
+                if last_import.module > record.module:
+                    yield self._error(
+                        record, 'B407',
+                        'From-imports not sorted alphabetically')
+                # All imports from the same module should show up in the same
+                # multiline import.
+                if last_import.module == record.module:
+                    yield self._error(
+                        record, 'B408',
+                        'Importing from same module on different lines')
+                # Check the sort order of the imported names.
+                if sorted(record.names) != record.names:
+                    yield self._error(
+                        record, 'B409',
+                        'Imported names are not sorted alphabetically')
+                # How to check for no blank lines between from imports?
+            # Update the last import.
+            last_import = record