check for variable reuse in nested for loops

closure_linter/error_check.py

@@ -37,6 +37,7 @@ class Rule(object):
   VARIABLE_ARG_MARKER = 'variable_arg_marker'
   UNUSED_PRIVATE_MEMBERS = 'unused_private_members'
   UNUSED_LOCAL_VARIABLES = 'unused_local_variables'
+  REUSED_LOOP_VARIABLE = 'reused_loop_variable'
 
   # Rule to raise all known errors.
   ALL = 'all'
@@ -49,7 +50,8 @@ class Rule(object):
                              NO_BRACES_AROUND_INHERIT_DOC,
                              BRACES_AROUND_TYPE,
                              OPTIONAL_TYPE_MARKER,
-                             VARIABLE_ARG_MARKER])
+                             VARIABLE_ARG_MARKER,
+                             REUSED_LOOP_VARIABLE])
 
 
 flags.DEFINE_boolean('strict', False,

closure_linter/errors.py

@@ -139,6 +139,8 @@ def ByName(name):
 REMOVE_COMMENT_BEFORE_SUBMIT = 1254
 # End of list of ActionScript specific errors.
 
+REUSED_LOOP_VARIABLE = 5000
+
 NEW_ERRORS = frozenset([
     # Errors added after 2.0.2:
     WRONG_INDENTATION,

closure_linter/full_test.py

@@ -61,6 +61,7 @@
     'jsdoc.js',
     'limited_doc_checks.js',
     'minimal.js',
+    'nested_loops.js',
     'other.js',
     'provide_blank.js',
     'provide_extra.js',

closure_linter/javascriptlintrules.py

@@ -80,6 +80,9 @@ def CheckToken(self, token, state):
     if error_check.ShouldCheck(Rule.UNUSED_LOCAL_VARIABLES):
       self._CheckUnusedLocalVariables(token, state)
 
+    if error_check.ShouldCheck(Rule.REUSED_LOOP_VARIABLE):
+      self._CheckReusedLoopVariable(token, state)
+
     if error_check.ShouldCheck(Rule.UNUSED_PRIVATE_MEMBERS):
       # Find all assignments to private members.
       if token.type == Type.SIMPLE_LVALUE:
@@ -597,6 +600,60 @@ def _MarkLocalVariableUsed(self, identifier):
         del unused_local_variables[identifier]
         break
 
+  def _CheckReusedLoopVariable(self, token, state):
+    """Checks for reused variables in for loops.
+
+    Args:
+      token: The token to check.
+      state: The state tracker.
+    """
+    def forLoopVarIdentifier(start_token):
+      """ returns the identifier for the var declaration, None if it is not present. """
+      var_token = tokenutil.CustomSearch(
+        start_token,
+        lambda t: t.IsKeyword('var'),
+        end_func=lambda t: t.type == Type.SEMICOLON,
+        distance=None)
+      if var_token:
+        ident_token = tokenutil.CustomSearch(
+          var_token,
+          lambda t: t.type == Type.SIMPLE_LVALUE,
+          end_func=lambda t: t.type == Type.SEMICOLON,
+          distance=None)
+        if ident_token:
+          var_ident = ident_token.string
+          return var_ident
+      return None
+
+    if token.IsKeyword('for'):
+      var_ident = forLoopVarIdentifier(token)
+
+      block_token = tokenutil.CustomSearch(
+        token,
+        lambda t: t.type == Type.START_BLOCK,
+        end_func=lambda t: t.type == Type.END_BLOCK,
+        distance=None)
+      block_counter = 1
+
+      # check nested for loops for their variable declarations
+      if block_token:
+        next_token = block_token.next
+        while block_counter:
+          if next_token.IsKeyword('for'):
+            inner_var_ident = forLoopVarIdentifier(next_token)
+            if inner_var_ident and inner_var_ident == var_ident:
+              reused_loop_ident_msg = 'Reused loop variable %s' % (var_ident, )
+              self._HandleError(
+                  errors.REUSED_LOOP_VARIABLE,
+                  reused_loop_ident_msg,
+                  token, position=Position.AtBeginning())
+          elif next_token.type == Type.START_BLOCK:
+            block_counter += 1
+          elif next_token.type == Type.END_BLOCK:
+            block_counter -= 1
+          next_token = next_token.next
+
+
   def _ReportMissingProvides(self, missing_provides, token, need_blank_line):
     """Reports missing provide statements to the error handler.
 

closure_linter/testdata/nested_loops.js

@@ -0,0 +1,27 @@
+
+// Reuse of i
+for (var i = 0; i < 10; i++) {
+  for (var i = 3; i < 5; i++) {
+  }
+}
+
+
+// Reuse of j
+for (var j = 10; j < 50; j++) {
+  for (var q = 0; q < 20; q++) {
+    for (var j = 7; j < 10; j++) {
+
+    }
+  }
+}
+
+// Reuse of r
+for (var q = 10; q < 50; q++) {
+  for (var r = 0; r < 20; r++) {
+    for (var r = 7; r < 10; r++) {
+
+    }
+  }
+}
+
+