Allow used variables to be properly consumed when different checks ar…

…e enabled / disabled

When everything else was disabled, except `unused-import`, pylint was emitting `unused-import`
even though the imports in questions were used.
The emission occurred due to the fact that disabling all the messages also disabled the calling
of `visit_name`, which deals with `undefined-variable`. This resulted in `visit_name` not marking
as consumed the earlier import as expected.
This fix still allows `visit_name` to be called, but the emission of `undefined-variable` and friends
is controlled via a flag prior to emission call site.

This is somewhat of a "temporary" hack, a better solution would be to separate the emission / checking
of undefined variable from marking the variables as consumed.

Close #3445

ChangeLog

@@ -11,6 +11,10 @@ Release date: TBA
 
   Close #2725
 
+* Allow used variables to be properly consumed when different checks are enabled / disabled
+
+  Close #3445
+
 * Fix dangerous-default-value rule to account for keyword argument defaults
 
   Close #3373

pylint/checkers/variables.py

@@ -936,12 +936,6 @@ def visit_assignname(self, node):
     def visit_delname(self, node):
         self.visit_name(node)
 
-    @utils.check_messages(
-        "cell-var-from-loop",
-        "undefined-loop-variable",
-        "undefined-variable",
-        "used-before-assignment",
-    )
     def visit_name(self, node):
         """Check that a name is defined in the current scope"""
         stmt = node.statement()
@@ -963,6 +957,14 @@ def visit_name(self, node):
             start_index = len(self._to_consume) - 2
         else:
             start_index = len(self._to_consume) - 1
+
+        undefined_variable_is_enabled = self.linter.is_message_enabled(
+            "undefined-variable"
+        )
+        used_before_assignment_is_enabled = self.linter.is_message_enabled(
+            "used-before-assignment"
+        )
+
         # iterates through parent scopes, from the inner to the outer
         base_scope_type = self._to_consume[start_index].scope_type
         # pylint: disable=too-many-nested-blocks; refactoring this block is a pain.
@@ -1001,7 +1003,9 @@ def visit_name(self, node):
             # checks for use before assignment
             defnode = utils.assign_parent(current_consumer.to_consume[name][0])
 
-            if defnode is not None:
+            if (
+                undefined_variable_is_enabled or used_before_assignment_is_enabled
+            ) and defnode is not None:
                 self._check_late_binding_closure(node, defnode)
                 defstmt = defnode.statement()
                 defframe = defstmt.frame()
@@ -1136,7 +1140,7 @@ def visit_name(self, node):
         else:
             # we have not found the name, if it isn't a builtin, that's an
             # undefined name !
-            if not (
+            if undefined_variable_is_enabled and not (
                 name in astroid.Module.scope_attrs
                 or utils.is_builtin(name)
                 or name in self.config.additional_builtins
@@ -1637,6 +1641,9 @@ def _check_unused_arguments(self, name, node, stmt, argnames):
         self.add_message("unused-argument", args=name, node=stmt, confidence=confidence)
 
     def _check_late_binding_closure(self, node, assignment_node):
+        if not self.linter.is_message_enabled("cell-var-from-loop"):
+            return
+
         def _is_direct_lambda_call():
             return (
                 isinstance(node_scope.parent, astroid.Call)

tests/functional/u/unused_import_everything_disabled.py

@@ -0,0 +1,8 @@
+"""Test that unused-import is not emitted here when everything else is disabled
+
+https://github.com/PyCQA/pylint/issues/3445
+"""
+from os import environ
+
+for k, v in environ.items():
+    print(k, v)

tests/functional/u/unused_import_everything_disabled.rc

@@ -0,0 +1,3 @@
+[Messages Control]
+disable=all
+enable=unused-import