[compare-to-empty-string] More actionnable and understandable message

We have to use " as string delimiter because node as string have ' as
string delimiter.

Author: Pierre-Sassoulas

pylint/extensions/emptystring.py

@@ -20,18 +20,10 @@
 
 
 class CompareToEmptyStringChecker(checkers.BaseChecker):
-    """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!
-    """
-
-    # configuration section name
     name = "compare-to-empty-string"
     msgs = {
         "C1901": (
-            "Avoid comparisons to empty string",
+            '"%s" can be simplified to "%s" as an empty string is falsey',
             "compare-to-empty-string",
             "Used when Pylint detects comparison to an empty string constant.",
         )
@@ -41,31 +33,45 @@ class CompareToEmptyStringChecker(checkers.BaseChecker):
 
     @utils.only_required_for_messages("compare-to-empty-string")
     def visit_compare(self, node: nodes.Compare) -> 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
+        """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) and op_2 in _operators:
+            if utils.is_empty_str_literal(op_1):
                 error_detected = True
+                node_name = op_3.as_string()
             # '' ?? X
-            elif op_2 in _operators and utils.is_empty_str_literal(op_3):
+            elif utils.is_empty_str_literal(op_3):
                 error_detected = True
-
+                node_name = op_1.as_string()
             if error_detected:
-                self.add_message("compare-to-empty-string", node=node, confidence=HIGH)
+                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 register(linter: PyLinter) -> None:

tests/functional/ext/emptystring/empty_string_comparison.txt

@@ -1,4 +1,4 @@
-compare-to-empty-string:6:3:6:10::Avoid comparisons to empty string:HIGH
-compare-to-empty-string:9:3:9:14::Avoid comparisons to empty string:HIGH
-compare-to-empty-string:12:3:12:10::Avoid comparisons to empty string:HIGH
-compare-to-empty-string:15:3:15:10::Avoid comparisons to empty string:HIGH
+compare-to-empty-string:6:3:6:10::"""X is ''"" can be simplified to ""not X"" as an empty string is falsey":HIGH
+compare-to-empty-string:9:3:9:14::"""Y is not ''"" can be simplified to ""Y"" as an empty string is falsey":HIGH
+compare-to-empty-string:12:3:12:10::"""X == ''"" can be simplified to ""not X"" as an empty string is falsey":HIGH
+compare-to-empty-string:15:3:15:10::"""Y != ''"" can be simplified to ""Y"" as an empty string is falsey":HIGH