Rule duplication `F509` and `PLE1300`

[Dhruv Manilawala]

Both rules check for invalid format character in % format style string.

The implementation is almost the same:

F509

ruff/crates/ruff_linter/src/checkers/ast/analyze/expression.rs

Lines 1087 to 1100 in 1f748b8

 match pyflakes::cformat::CFormatSummary::try_from(value.to_str()) { 
     Err(CFormatError { 
         typ: CFormatErrorType::UnsupportedFormatChar(c), 
         .. 
     }) => { 
         if checker.enabled(Rule::PercentFormatUnsupportedFormatCharacter) { 
             checker.diagnostics.push(Diagnostic::new( 
                 pyflakes::rules::PercentFormatUnsupportedFormatCharacter { 
                     char: c, 
                 }, 
                 location, 
             )); 
         } 
     } 

PLE1300

ruff/crates/ruff_linter/src/rules/pylint/rules/bad_string_format_character.rs

Lines 117 to 125 in 1f748b8

 // Parse the format string (e.g. `"%s"`) into a list of `PercentFormat`. 
 if let Err(format_error) = CFormatString::from_str(string) { 
     if let CFormatErrorType::UnsupportedFormatChar(format_char) = format_error.typ { 
         checker.diagnostics.push(Diagnostic::new( 
             BadStringFormatCharacter { format_char }, 
             expr.range(), 
         )); 
     } 
 }; 

There's one difference which can be noticed when an implicitly concatenated string is used. F509 looks at the concatenated string while PLE1300 looks at each part of an implicitly concatenated string. Refer to https://play.ruff.rs/6efd9945-2a3b-43e4-b9b7-a8d041b98318.

Reference:

• F509 https://docs.astral.sh/ruff/rules/percent-format-unsupported-format-character/
• PLE1300 https://docs.astral.sh/ruff/rules/bad-string-format-character/

[Charlie Marsh]

@dhruvmanila - Let's remove PLE1300 as part of v0.5.0?

[Zanie Blue]

See #9756 for prior art.

[Dhruv Manilawala]

Let's remove PLE1300 as part of v0.5.0?

Yeah, that makes sense but there's one difference where PLE1300 would check each part of an implicitly concatenated string while F509 checks it as a whole. This means that the number of diagnostics would be reduced. That said, I think F509 can be improved to either

1. Include all the invalid characters in the message or
2. Raise violation for each invalid character and highlighting the part of the string instead of the entire string