Merge the empty-string extensions to 'implicit_booleaness_checker'

Author: Pierre-Sassoulas

doc/data/messages/c/compare-to-empty-string/bad.py

@@ -0,0 +1,6 @@
+def important_string_manipulation(x: str, y: str) -> None:
+    if x == "":  # [use-implicit-booleaness-not-comparison-to-string]
+        print("x is an empty string")
+
+    if y != "":  # [use-implicit-booleaness-not-comparison-to-string]
+        print("y is not an empty string")

doc/data/messages/c/compare-to-empty-string/good.py

@@ -0,0 +1,3 @@
+Following this check blindly in weakly typed code base can create hard to debug issues. If the value
+can be something else that is falsey but not a string (for example ``None``, or ``0``), the code will
+not be equivalent.

doc/data/messages/c/compare-to-empty-string/pylintrc

@@ -0,0 +1,6 @@
+def important_string_manipulation(x: str, y: str) -> None:
+    if not x:
+        print("x is an empty string")
+
+    if y:
+        print("y is not an empty string")

doc/data/messages/u/use-implicit-booleaness-not-comparison-to-string/bad.py

@@ -0,0 +1,2 @@
+[main]
+enable=use-implicit-booleaness-not-comparison-to-string

doc/data/messages/u/use-implicit-booleaness-not-comparison-to-string/details.rst

@@ -19,7 +19,6 @@ Pylint provides the following optional plugins:
 - :ref:`pylint.extensions.docstyle`
 - :ref:`pylint.extensions.dunder`
 - :ref:`pylint.extensions.empty_comment`
-- :ref:`pylint.extensions.emptystring`
 - :ref:`pylint.extensions.eq_without_hash`
 - :ref:`pylint.extensions.for_any_all`
 - :ref:`pylint.extensions.magic_value`
@@ -87,20 +86,6 @@ Code Style checker Messages
   to. This can be changed to be an augmented assign. Disabled by default!
 
 
-.. _pylint.extensions.emptystring:
-
-Compare-To-Empty-String checker
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-This checker is provided by ``pylint.extensions.emptystring``.
-Verbatim name of the checker is ``compare-to-empty-string``.
-
-Compare-To-Empty-String checker Messages
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-:compare-to-empty-string (C1901): *"%s" can be simplified to "%s" as an empty string is falsey*
-  Used when Pylint detects comparison to an empty string constant.
-
-
 .. _pylint.extensions.comparison_placement:
 
 Comparison-Placement checker

doc/data/messages/u/use-implicit-booleaness-not-comparison-to-string/good.py

@@ -893,8 +893,10 @@ Refactoring checker Messages
   Emitted when a single "return" or "return None" statement is found at the end
   of function or method definition. This statement can safely be removed
   because Python will implicitly return None
-:use-implicit-booleaness-not-comparison-to-zero (C1804): *"%s" can be simplified to "%s" as 0 is falsey*
+:use-implicit-booleaness-not-comparison-to-zero (C1805): *"%s" can be simplified to "%s" as 0 is falsey*
   Used when Pylint detects comparison to a 0 constant.
+:use-implicit-booleaness-not-comparison-to-string (C1804): *"%s" can be simplified to "%s" as an empty string is falsey*
+  Used when Pylint detects comparison to an empty string constant.
 :use-implicit-booleaness-not-comparison (C1803): *'%s' can be simplified to '%s' as an empty %s is falsey*
   Used when Pylint detects that collection literal comparison is being used to
   check for emptiness; Use implicit booleaness instead of a collection classes;

doc/data/messages/u/use-implicit-booleaness-not-comparison-to-string/pylintrc

@@ -233,7 +233,7 @@ Standard Checkers
 
    confidence = ["HIGH", "CONTROL_FLOW", "INFERENCE", "INFERENCE_FAILURE", "UNDEFINED"]
 
-   disable = ["raw-checker-failed", "bad-inline-option", "locally-disabled", "file-ignored", "suppressed-message", "useless-suppression", "deprecated-pragma", "use-implicit-booleaness-not-comparison-to-zero", "use-symbolic-message-instead", "consider-using-augmented-assign"]
+   disable = ["raw-checker-failed", "bad-inline-option", "locally-disabled", "file-ignored", "suppressed-message", "useless-suppression", "deprecated-pragma", "use-implicit-booleaness-not-comparison-to-string", "use-implicit-booleaness-not-comparison-to-zero", "use-symbolic-message-instead", "consider-using-augmented-assign"]
 
    enable = []
 

doc/user_guide/checkers/extensions.rst

@@ -390,7 +390,6 @@ All messages in the convention category:
    convention/bad-file-encoding
    convention/bad-mcs-classmethod-argument
    convention/bad-mcs-method-argument
-   convention/compare-to-empty-string
    convention/consider-iterating-dictionary
    convention/consider-using-any-or-all
    convention/consider-using-dict-items
@@ -432,6 +431,7 @@ All messages in the convention category:
    convention/unnecessary-lambda-assignment
    convention/unneeded-not
    convention/use-implicit-booleaness-not-comparison
+   convention/use-implicit-booleaness-not-comparison-to-string
    convention/use-implicit-booleaness-not-comparison-to-zero
    convention/use-implicit-booleaness-not-len
    convention/use-maxsplit-arg
@@ -449,6 +449,7 @@ All renamed messages in the convention category:
    :titlesonly:
 
    convention/blacklisted-name
+   convention/compare-to-empty-string
    convention/compare-to-zero
    convention/len-as-condition
    convention/missing-docstring

doc/user_guide/checkers/features.rst

@@ -1,12 +1,14 @@
-* The compare to empty string checker (``pylint.extensions.emptystring``) has been removed and its checks are
+* The compare to empty string checker (``pylint.extensions.emptystring``) and the compare to
+  zero checker (``pylint.extensions.compare-to-zero``) have been removed and their checks are
   now part of the implicit booleaness checker:
 
   - ``compare-to-zero`` was renamed ``use-implicit-booleaness-not-comparison-to-zero``
-    and it now need to be enabled explicitly.
-  - The ``pylint.extensions.compare-to-zero`` extension no longer exists and
+    and ``compare-to-empty-string`` was renamed ``use-implicit-booleaness-not-comparison-to-string``
+    and they now need to be enabled explicitly.
+  - The `pylint.extensions.emptystring`` and ``pylint.extensions.compare-to-zero`` extensions no longer exists and
     needs to be removed from the ``load-plugins`` option.
 
-This permits to make the likeness explicit and will provide better performance as they share most of their
+This permits to make their likeness explicit and will provide better performance as they share most of their
 conditions to be raised.
 
 Refs #6871

doc/user_guide/configuration/all-options.rst

@@ -81,6 +81,15 @@ class ImplicitBooleanessChecker(checkers.BaseChecker):
             "of a collection classes; empty collections are considered as false",
         ),
         "C1804": (
+            '"%s" can be simplified to "%s" as an empty string is falsey',
+            "use-implicit-booleaness-not-comparison-to-string",
+            "Used when Pylint detects comparison to an empty string constant.",
+            {
+                "default_enabled": False,
+                "old_names": [("C1901", "compare-to-empty-string")],
+            },
+        ),
+        "C1805": (
             '"%s" can be simplified to "%s" as 0 is falsey',
             "use-implicit-booleaness-not-comparison-to-zero",
             "Used when Pylint detects comparison to a 0 constant.",
@@ -162,12 +171,16 @@ def visit_unaryop(self, node: nodes.UnaryOp) -> None:
                 "use-implicit-booleaness-not-len", node=node, confidence=HIGH
             )
 
-    @utils.only_required_for_messages("use-implicit-booleaness-not-comparison")
+    @utils.only_required_for_messages(
+        "use-implicit-booleaness-not-comparison",
+        "use-implicit-booleaness-not-comparison-to-string",
+        "use-implicit-booleaness-not-comparison-to-zero",
+    )
     def visit_compare(self, node: nodes.Compare) -> None:
         self._check_use_implicit_booleaness_not_comparison(node)
         self._check_compare_to_zero(node)
+        self._check_compare_to_string(node)
 
-    @utils.only_required_for_messages("compare-to-zero")
     def _check_compare_to_zero(self, node: nodes.Compare) -> None:
         # pylint: disable=duplicate-code
         _operators = ["!=", "==", "is not", "is"]
@@ -209,6 +222,47 @@ def _check_compare_to_zero(self, node: nodes.Compare) -> None:
                     confidence=HIGH,
                 )
 
+    def _check_compare_to_string(self, node: nodes.Compare) -> None:
+        """Checks for comparisons to empty string.
+
+        Most of the time you should use the fact that empty strings are false.
+        An exception to this rule is when an empty string value is allowed in the program
+        and has a different meaning than None!
+        """
+        _operators = {"!=", "==", "is not", "is"}
+        # note: astroid.Compare has the left most operand in node.left while the rest
+        # are a list of tuples in node.ops the format of the tuple is
+        # ('compare operator sign', node) here we squash everything into `ops`
+        # to make it easier for processing later
+        ops: list[tuple[str, nodes.NodeNG | None]] = [("", node.left)]
+        ops.extend(node.ops)
+        iter_ops = iter(ops)
+        ops = list(itertools.chain(*iter_ops))  # type: ignore[arg-type]
+        for ops_idx in range(len(ops) - 2):
+            op_1: nodes.NodeNG | None = ops[ops_idx]
+            op_2: str = ops[ops_idx + 1]  # type: ignore[assignment]
+            op_3: nodes.NodeNG | None = ops[ops_idx + 2]
+            error_detected = False
+            if op_1 is None or op_3 is None or op_2 not in _operators:
+                continue
+            node_name = ""
+            # x ?? ""
+            if utils.is_empty_str_literal(op_1):
+                error_detected = True
+                node_name = op_3.as_string()
+            # '' ?? X
+            elif utils.is_empty_str_literal(op_3):
+                error_detected = True
+                node_name = op_1.as_string()
+            if error_detected:
+                suggestion = f"not {node_name}" if op_2 in {"==", "is"} else node_name
+                self.add_message(
+                    "compare-to-empty-string",
+                    args=(node.as_string(), suggestion),
+                    node=node,
+                    confidence=HIGH,
+                )
+
     def _check_use_implicit_booleaness_not_comparison(
         self, node: nodes.Compare
     ) -> None:

doc/user_guide/messages/messages_overview.rst

@@ -0,0 +1,22 @@
+# pylint: disable=literal-comparison,missing-docstring
+
+X = ''
+Y = 'test'
+
+if X is '':  # [use-implicit-booleaness-not-comparison-to-string]
+    pass
+
+if Y is not "":  # [use-implicit-booleaness-not-comparison-to-string]
+    pass
+
+if X == "":  # [use-implicit-booleaness-not-comparison-to-string]
+    pass
+
+if Y != '':  # [use-implicit-booleaness-not-comparison-to-string]
+    pass
+
+if "" == Y:  # [use-implicit-booleaness-not-comparison-to-string]
+    pass
+
+if '' != X:  # [use-implicit-booleaness-not-comparison-to-string]
+    pass

doc/whatsnew/fragments/6871.user_action

@@ -0,0 +1,2 @@
+[MAIN]
+enable=use-implicit-booleaness-not-comparison-to-string

pylint/checkers/refactoring/implicit_booleaness_checker.py

@@ -0,0 +1,6 @@
+use-implicit-booleaness-not-comparison-to-string:6:3:6:10::"""X is ''"" can be simplified to ""not X"" as an empty string is falsey":HIGH
+use-implicit-booleaness-not-comparison-to-string:9:3:9:14::"""Y is not ''"" can be simplified to ""Y"" as an empty string is falsey":HIGH
+use-implicit-booleaness-not-comparison-to-string:12:3:12:10::"""X == ''"" can be simplified to ""not X"" as an empty string is falsey":HIGH
+use-implicit-booleaness-not-comparison-to-string:15:3:15:10::"""Y != ''"" can be simplified to ""Y"" as an empty string is falsey":HIGH
+use-implicit-booleaness-not-comparison-to-string:18:3:18:10::"""'' == Y"" can be simplified to ""not Y"" as an empty string is falsey":HIGH
+use-implicit-booleaness-not-comparison-to-string:21:3:21:10::"""'' != X"" can be simplified to ""X"" as an empty string is falsey":HIGH