Add support for nested replacements inside format specifications

crates/ruff/resources/test/fixtures/pylint/bad_string_format_character.py

@@ -14,7 +14,10 @@
 
 "{:s} {:y}".format("hello", "world") # [bad-format-character]
 
-"{:*^30s}".format("centered")
+"{:*^30s}".format("centered") # OK
+"{:{s}}".format("hello", s="s") # OK (nested replacement value not checked)
+
+"{:{s:y}}".format("hello", s="s") # [bad-format-character] (nested replacement format spec checked)
 
 ## f-strings
 

crates/ruff/src/rules/pyflakes/format.rs

@@ -11,7 +11,9 @@ pub(crate) fn error_to_string(err: &FormatParseError) -> String {
  FormatParseError::InvalidCharacterAfterRightBracket => {
  "Only '.' or '[' may follow ']' in format field specifier"
  }
- FormatParseError::InvalidFormatSpecifier => "Max string recursion exceeded",
+ FormatParseError::PlaceholderRecursionExceeded => {
+ "Max format placeholder recursion exceeded"
+ }
  FormatParseError::MissingStartBracket => "Single '}' encountered in format string",
  FormatParseError::MissingRightBracket => "Expected '}' before end of string",
  FormatParseError::UnmatchedBracket => "Single '{' encountered in format string",

crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F521_F521.py.snap

@@ -28,7 +28,7 @@ F521.py:3:1: F521 `.format` call has invalid format string: Expected '}' before
 5 | "{:{:{}}}".format(1, 2, 3)
  |
 
-F521.py:5:1: F521 `.format` call has invalid format string: Max string recursion exceeded
+F521.py:5:1: F521 `.format` call has invalid format string: Max format placeholder recursion exceeded
  |
 3 | "{foo[}".format(foo=1)
 4 | # too much string recursion (placeholder-in-placeholder)

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

@@ -49,16 +49,39 @@ pub(crate) fn call(checker: &mut Checker, string: &str, range: TextRange) {
  continue;
  };
 
- if let Err(FormatSpecError::InvalidFormatType) = FormatSpec::parse(format_spec) {
- checker.diagnostics.push(Diagnostic::new(
- BadStringFormatCharacter {
- // The format type character is always the last one.
- // More info in the official spec:
- // https://docs.python.org/3/library/string.html#format-specification-mini-language
- format_char: format_spec.chars().last().unwrap(),
- },
- range,
- ));
+ match FormatSpec::parse(format_spec) {
+ Err(FormatSpecError::InvalidFormatType) => {
+ checker.diagnostics.push(Diagnostic::new(
+ BadStringFormatCharacter {
+ // The format type character is always the last one.
+ // More info in the official spec:
+ // https://docs.python.org/3/library/string.html#format-specification-mini-language
+ format_char: format_spec.chars().last().unwrap(),
+ },
+ range,
+ ));
+ }
+ Err(_) => {}
+ Ok(format_spec) => {
+ for replacement in format_spec.replacements() {
+ let FormatPart::Field { format_spec, .. } = replacement else {
+ continue;
+ };
+ if let Err(FormatSpecError::InvalidFormatType) =
+ FormatSpec::parse(format_spec)
+ {
+ checker.diagnostics.push(Diagnostic::new(
+ BadStringFormatCharacter {
+ // The format type character is always the last one.
+ // More info in the official spec:
+ // https://docs.python.org/3/library/string.html#format-specification-mini-language
+ format_char: format_spec.chars().last().unwrap(),
+ },
+ range,
+ ));
+ }
+ }
+ }
  }
  }
  }

crates/ruff/src/rules/pylint/snapshots/ruff__rules__pylint__tests__PLE1300_bad_string_format_character.py.snap

@@ -48,7 +48,17 @@ bad_string_format_character.py:15:1: PLE1300 Unsupported format character 'y'
 15 | "{:s} {:y}".format("hello", "world") # [bad-format-character]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PLE1300
 16 | 
-17 | "{:*^30s}".format("centered")
+17 | "{:*^30s}".format("centered") # OK
+ |
+
+bad_string_format_character.py:20:1: PLE1300 Unsupported format character 'y'
+ |
+18 | "{:{s}}".format("hello", s="s") # OK (nested replacement value not checked)
+19 | 
+20 | "{:{s:y}}".format("hello", s="s") # [bad-format-character] (nested replacement format spec checked)
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ PLE1300
+21 | 
+22 | ## f-strings
  |