Optionally disable consider-using-join for non-empty separator (pylin…

…t-dev#9129)

* Skip consider-using-join for non-empty separators

Only suggest joining with separators when a new option
'suggest-join-with-non-empty-separator' is specified.

Co-authored-by: Pierre Sassoulas <[email protected]>

doc/user_guide/configuration/all-options.rst

@@ -1196,6 +1196,14 @@ Standard Checkers
 **Default:**  ``('sys.exit', 'argparse.parse_error')``
 
 
+--suggest-join-with-non-empty-separator
+"""""""""""""""""""""""""""""""""""""""
+*Let 'consider-using-join' be raised when the separator to join on would be non-empty (resulting in expected fixes of the type: ``"- " + "
+- ".join(items)``)*
+
+**Default:**  ``True``
+
+
 
 .. raw:: html
 
@@ -1211,6 +1219,8 @@ Standard Checkers
 
    never-returning-functions = ["sys.exit", "argparse.parse_error"]
 
+   suggest-join-with-non-empty-separator = true
+
 
 
 .. raw:: html

doc/whatsnew/fragments/8701.feature

@@ -0,0 +1,3 @@
+Skip ``consider-using-join`` check for non-empty separators if an ``suggest-join-with-non-empty-separator`` option is set to ``no``.
+
+Closes #8701

pylint/checkers/refactoring/refactoring_checker.py

@@ -506,6 +506,19 @@ class RefactoringChecker(checkers.BaseTokenChecker):
                 "and no message will be printed.",
             },
         ),
+        (
+            "suggest-join-with-non-empty-separator",
+            {
+                "default": True,
+                "type": "yn",
+                "metavar": "<y or n>",
+                "help": (
+                    "Let 'consider-using-join' be raised when the separator to "
+                    "join on would be non-empty (resulting in expected fixes "
+                    'of the type: ``"- " + "\n- ".join(items)``)'
+                ),
+            },
+        ),
     )
 
     def __init__(self, linter: PyLinter) -> None:
@@ -514,6 +527,7 @@ def __init__(self, linter: PyLinter) -> None:
         self._consider_using_with_stack = ConsiderUsingWithStack()
         self._init()
         self._never_returning_functions: set[str] = set()
+        self._suggest_join_with_non_empty_separator: bool = False
 
     def _init(self) -> None:
         self._nested_blocks: list[NodesWithNestedBlocks] = []
@@ -527,6 +541,9 @@ def open(self) -> None:
         self._never_returning_functions = set(
             self.linter.config.never_returning_functions
         )
+        self._suggest_join_with_non_empty_separator = (
+            self.linter.config.suggest_join_with_non_empty_separator
+        )
 
     @cached_property
     def _dummy_rgx(self) -> Pattern[str]:
@@ -1667,8 +1684,7 @@ def _dict_literal_suggestion(node: nodes.Call) -> str:
         suggestion = ", ".join(elements)
         return f"{{{suggestion}{', ... '  if len(suggestion) > 64 else ''}}}"
 
-    @staticmethod
-    def _name_to_concatenate(node: nodes.NodeNG) -> str | None:
+    def _name_to_concatenate(self, node: nodes.NodeNG) -> str | None:
         """Try to extract the name used in a concatenation loop."""
         if isinstance(node, nodes.Name):
             return cast("str | None", node.name)
@@ -1680,6 +1696,12 @@ def _name_to_concatenate(node: nodes.NodeNG) -> str | None:
         ]
         if len(values) != 1 or not isinstance(values[0].value, nodes.Name):
             return None
+        # If there are more values in joined string than formatted values,
+        # they are probably separators.
+        # Allow them only if the option `suggest-join-with-non-empty-separator` is set
+        with_separators = len(node.values) > len(values)
+        if with_separators and not self._suggest_join_with_non_empty_separator:
+            return None
         return cast("str | None", values[0].value.name)
 
     def _check_consider_using_join(self, aug_assign: nodes.AugAssign) -> None:

tests/functional/c/consider/consider_join_for_non_empty_separator.py

@@ -0,0 +1,24 @@
+# pylint: disable=missing-docstring,invalid-name,undefined-variable,multiple-statements
+
+result = 'a'
+for number in ['1', '2', '3']:
+    result += f'b{number}'
+assert result == 'ab1b2b3'
+assert result == 'b'.join(['a', '1', '2', '3'])
+
+result = 'a'
+for number in ['1', '2', '3']:
+    result += f'{number}c'
+assert result == 'a1c2c3c'
+assert result == 'a' + 'c'.join(['1', '2', '3']) + 'c'
+
+result = 'a'
+for number in ['1', '2', '3']:
+    result += f'b{number}c'
+assert result == 'ab1cb2cb3c'
+assert result == 'ab' + 'cb'.join(['1', '2', '3']) + 'c'
+
+result = ''
+for number in ['1', '2', '3']:
+    result += f"{number}, "
+result = result[:-2]

tests/functional/c/consider/consider_join_for_non_empty_separator.rc

@@ -0,0 +1,2 @@
+[variables]
+suggest-join-with-non-empty-separator=no