pylint extension to check for use of "else if" instead of "elsif"

related to issue #673

1 files changed, 76 insertions, 0 deletions

diff --git a/pylint/extensions/check_elif.py b/pylint/extensions/check_elif.py
new file mode 100644
index 0000000..e9f2dfa
--- /dev/null
+++ b/pylint/extensions/check_elif.py
@@ -0,0 +1,76 @@
+import astroid
+from pylint.checkers import BaseTokenChecker
+from pylint.checkers.utils import check_messages
+from pylint.interfaces import ITokenChecker, IAstroidChecker
+
+
+class ElseifUsedChecker(BaseTokenChecker):
+    """Checks for use of "else if" when a "elif" could be used
+    """
+
+    __implements__ = (ITokenChecker, IAstroidChecker)
+    name = 'elseifused'
+    msgs = {'R5501': ('Consider using "elif" instead of "else if"',
+                      'else-if-used',
+                      'Used when an else statement is immediately followed by '
+                      'an if statement and does not contain statements that '
+                      'would be unrelated to it.'),
+           }
+
+    def __init__(self, linter=None):
+        BaseTokenChecker.__init__(self, linter)
+        self._init()
+
+    def _init(self):
+        self._elifs = []
+        self._if_counter = 0
+
+    def _is_actual_elif(self, node):
+        """Check if the given node is an actual elif
+
+        This is a problem we're having with the builtin ast module,
+        which splits `elif` branches into a separate if statement.
+        Unfortunately we need to know the exact type in certain
+        cases.
+        """
+
+        if isinstance(node.parent, astroid.If):
+            orelse = node.parent.orelse
+            # current if node must directly follow a "else"
+            if orelse and orelse == [node]:
+                if self._elifs[self._if_counter]:
+                    return True
+        return False
+
+    def process_tokens(self, tokens):
+        # Process tokens and look for 'if' or 'elif'
+        for _, token, _, _, _ in tokens:
+            self._elifs.append(True if token == 'elif' else False)
+
+    def leave_module(self, _):
+        self._init()
+
+    def visit_ifexp(self, _):
+        self._if_counter += 1
+
+    def visit_comprehension(self, node):
+        self._if_counter += len(node.ifs)
+
+    @check_messages('else-if-used')
+    def visit_if(self, node):
+        if isinstance(node.parent, astroid.If):
+            orelse = node.parent.orelse
+            # current if node must directly follow a "else"
+            if orelse and orelse == [node]:
+                if not self._elifs[self._if_counter]:
+                    self.add_message('else-if-used', node=node)
+        self._if_counter += 1
+
+
+def register(linter):
+    """Required method to auto register this checker.
+
+    :param linter: Main interface object for Pylint plugins
+    :type linter: Pylint object
+    """
+    linter.register_checker(ElseifUsedChecker(linter))