Add new rule to check for useless quote escapes

crates/ruff_linter/resources/test/fixtures/flake8_quotes/doubles_escaped_unnecessary.py

@@ -0,0 +1,45 @@
+this_should_raise_Q004 = 'This is a \"string\"'
+this_should_raise_Q004 = 'This is \\ a \\\"string\"'
+this_is_fine = '"This" is a \"string\"'
+this_is_fine = "This is a 'string'"
+this_is_fine = "\"This\" is a 'string'"
+this_is_fine = r'This is a \"string\"'
+this_is_fine = R'This is a \"string\"'
+this_should_raise_Q004 = (
+    'This is a'
+    '\"string\"'
+)
+
+# Same as above, but with f-strings
+f'This is a \"string\"'  # Q004
+f'This is \\ a \\\"string\"'  # Q004
+f'"This" is a \"string\"'
+f"This is a 'string'"
+f"\"This\" is a 'string'"
+fr'This is a \"string\"'
+fR'This is a \"string\"'
+this_should_raise_Q004 = (
+    f'This is a'
+    f'\"string\"'  # Q004
+)
+
+# Nested f-strings (Python 3.12+)
+#
+# The first one is interesting because the fix for it is valid pre 3.12:
+#
+#   f"'foo' {'nested'}"
+#
+# but as the actual string itself is invalid pre 3.12, we don't catch it.
+f'\"foo\" {'nested'}'  # Q004
+f'\"foo\" {f'nested'}'  # Q004
+f'\"foo\" {f'\"nested\"'} \"\"'  # Q004
+
+f'normal {f'nested'} normal'
+f'\"normal\" {f'nested'} normal'  # Q004
+f'\"normal\" {f'nested'} "double quotes"'
+f'\"normal\" {f'\"nested\" {'other'} normal'} "double quotes"'  # Q004
+f'\"normal\" {f'\"nested\" {'other'} "double quotes"'} normal'  # Q004
+
+# Make sure we do not unescape quotes
+this_is_fine = 'This is an \\"escaped\\" quote'
+this_should_raise_Q004 = 'This is an \\\"escaped\\\" quote with an extra backslash'

crates/ruff_linter/resources/test/fixtures/flake8_quotes/singles_escaped_unnecessary.py

@@ -0,0 +1,43 @@
+this_should_raise_Q004 = "This is a \'string\'"
+this_should_raise_Q004 = "'This' is a \'string\'"
+this_is_fine = 'This is a "string"'
+this_is_fine = '\'This\' is a "string"'
+this_is_fine = r"This is a \'string\'"
+this_is_fine = R"This is a \'string\'"
+this_should_raise_Q004 = (
+    "This is a"
+    "\'string\'"
+)
+
+# Same as above, but with f-strings
+f"This is a \'string\'"  # Q004
+f"'This' is a \'string\'"  # Q004
+f'This is a "string"'
+f'\'This\' is a "string"'
+fr"This is a \'string\'"
+fR"This is a \'string\'"
+this_should_raise_Q004 = (
+    f"This is a"
+    f"\'string\'"  # Q004
+)
+
+# Nested f-strings (Python 3.12+)
+#
+# The first one is interesting because the fix for it is valid pre 3.12:
+#
+#   f'"foo" {"nested"}'
+#
+# but as the actual string itself is invalid pre 3.12, we don't catch it.
+f"\'foo\' {"foo"}"  # Q004
+f"\'foo\' {f"foo"}"  # Q004
+f"\'foo\' {f"\'foo\'"} \'\'"  # Q004
+
+f"normal {f"nested"} normal"
+f"\'normal\' {f"nested"} normal"  # Q004
+f"\'normal\' {f"nested"} 'single quotes'"
+f"\'normal\' {f"\'nested\' {"other"} normal"} 'single quotes'"  # Q004
+f"\'normal\' {f"\'nested\' {"other"} 'single quotes'"} normal"  # Q004
+
+# Make sure we do not unescape quotes
+this_is_fine = "This is an \\'escaped\\' quote"
+this_should_raise_Q004 = "This is an \\\'escaped\\\' quote with an extra backslash"

crates/ruff_linter/src/checkers/tokens.rs

@@ -115,6 +115,10 @@ pub(crate) fn check_tokens(
         flake8_quotes::rules::avoidable_escaped_quote(&mut diagnostics, tokens, locator, settings);
     }
 
+    if settings.rules.enabled(Rule::UnnecessaryEscapedQuote) {
+        flake8_quotes::rules::unnecessary_escaped_quote(&mut diagnostics, tokens, locator);
+    }
+
     if settings.rules.any_enabled(&[
         Rule::BadQuotesInlineString,
         Rule::BadQuotesMultilineString,

crates/ruff_linter/src/codes.rs

@@ -403,6 +403,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8Quotes, "001") => (RuleGroup::Stable, rules::flake8_quotes::rules::BadQuotesMultilineString),
         (Flake8Quotes, "002") => (RuleGroup::Stable, rules::flake8_quotes::rules::BadQuotesDocstring),
         (Flake8Quotes, "003") => (RuleGroup::Stable, rules::flake8_quotes::rules::AvoidableEscapedQuote),
+        (Flake8Quotes, "004") => (RuleGroup::Preview, rules::flake8_quotes::rules::UnnecessaryEscapedQuote),
 
         // flake8-annotations
         (Flake8Annotations, "001") => (RuleGroup::Stable, rules::flake8_annotations::rules::MissingTypeFunctionArgument),

crates/ruff_linter/src/rules/flake8_quotes/mod.rs

@@ -19,6 +19,7 @@ mod tests {
 
     #[test_case(Path::new("doubles.py"))]
     #[test_case(Path::new("doubles_escaped.py"))]
+    #[test_case(Path::new("doubles_escaped_unnecessary.py"))]
     #[test_case(Path::new("doubles_implicit.py"))]
     #[test_case(Path::new("doubles_multiline_string.py"))]
     #[test_case(Path::new("doubles_noqa.py"))]
@@ -39,6 +40,7 @@ mod tests {
                     Rule::BadQuotesMultilineString,
                     Rule::BadQuotesDocstring,
                     Rule::AvoidableEscapedQuote,
+                    Rule::UnnecessaryEscapedQuote,
                 ])
             },
         )?;
@@ -86,6 +88,7 @@ mod tests {
 
     #[test_case(Path::new("singles.py"))]
     #[test_case(Path::new("singles_escaped.py"))]
+    #[test_case(Path::new("singles_escaped_unnecessary.py"))]
     #[test_case(Path::new("singles_implicit.py"))]
     #[test_case(Path::new("singles_multiline_string.py"))]
     #[test_case(Path::new("singles_noqa.py"))]
@@ -106,6 +109,7 @@ mod tests {
                     Rule::BadQuotesMultilineString,
                     Rule::BadQuotesDocstring,
                     Rule::AvoidableEscapedQuote,
+                    Rule::UnnecessaryEscapedQuote,
                 ])
             },
         )?;
@@ -139,6 +143,7 @@ mod tests {
                     Rule::BadQuotesMultilineString,
                     Rule::BadQuotesDocstring,
                     Rule::AvoidableEscapedQuote,
+                    Rule::UnnecessaryEscapedQuote,
                 ])
             },
         )?;
@@ -172,6 +177,7 @@ mod tests {
                     Rule::BadQuotesMultilineString,
                     Rule::BadQuotesDocstring,
                     Rule::AvoidableEscapedQuote,
+                    Rule::UnnecessaryEscapedQuote,
                 ])
             },
         )?;