Allow multi-line f-string with format spec

crates/ruff_python_parser/src/lexer.rs

@@ -566,6 +566,9 @@ impl<'source> Lexer<'source> {
         // Tracks the last offset of token value that has been written to `normalized`.
         let mut last_offset = self.offset();
 
+        // This isn't going to change for the duration of the loop.
+        let in_format_spec = fstring.is_in_format_spec(self.nesting);
+
         let mut in_named_unicode = false;
 
         loop {
@@ -585,6 +588,24 @@ impl<'source> Lexer<'source> {
                     });
                 }
                 '\n' | '\r' if !fstring.is_triple_quoted() => {
+                    // If we encounter a newline while we're in a format spec, then
+                    // we stop here and let the lexer emit the newline token.
+                    //
+                    // This is not done for triple-quoted f-strings because newlines
+                    // are significant in those. For example,
+                    //
+                    // ```python
+                    // f"""__{
+                    //    datetime.datetime.now():%Y
+                    //    %m
+                    //    %d
+                    // }__"""
+                    //
+                    // # Output: '__2023\n   10\n   04\n__'
+                    // ```
+                    if in_format_spec {
+                        break;
+                    }
                     return Err(LexicalError {
                         error: LexicalErrorType::FStringError(FStringErrorType::UnterminatedString),
                         location: self.offset(),
@@ -620,7 +641,7 @@ impl<'source> Lexer<'source> {
                     }
                 }
                 '{' => {
-                    if self.cursor.second() == '{' && !fstring.is_in_format_spec(self.nesting) {
+                    if self.cursor.second() == '{' && !in_format_spec {
                         self.cursor.bump();
                         normalized
                             .push_str(&self.source[TextRange::new(last_offset, self.offset())]);
@@ -634,9 +655,7 @@ impl<'source> Lexer<'source> {
                     if in_named_unicode {
                         in_named_unicode = false;
                         self.cursor.bump();
-                    } else if self.cursor.second() == '}'
-                        && !fstring.is_in_format_spec(self.nesting)
-                    {
+                    } else if self.cursor.second() == '}' && !in_format_spec {
                         self.cursor.bump();
                         normalized
                             .push_str(&self.source[TextRange::new(last_offset, self.offset())]);
@@ -2051,6 +2070,16 @@ def f(arg=%timeit a = b):
         assert_debug_snapshot!(lex_source(source));
     }
 
+    #[test]
+    fn test_fstring_with_multiline_format_spec() {
+        let source = r"f'''__{
+    x:d
+}__''' f'__{
+    x:d
+}__'";
+        assert_debug_snapshot!(lex_source(source));
+    }
+
     #[test]
     fn test_fstring_conversion() {
         let source = r#"f"{x!s} {x=!r} {x:.3f!r} {{x!r}}""#;

crates/ruff_python_parser/src/snapshots/ruff_python_parser__lexer__tests__fstring_with_multiline_format_spec.snap

@@ -0,0 +1,116 @@
+---
+source: crates/ruff_python_parser/src/lexer.rs
+expression: lex_source(source)
+---
+[
+    (
+        FStringStart,
+        0..4,
+    ),
+    (
+        FStringMiddle {
+            value: "__",
+            is_raw: false,
+        },
+        4..6,
+    ),
+    (
+        Lbrace,
+        6..7,
+    ),
+    (
+        NonLogicalNewline,
+        7..8,
+    ),
+    (
+        Name {
+            name: "x",
+        },
+        12..13,
+    ),
+    (
+        Colon,
+        13..14,
+    ),
+    (
+        FStringMiddle {
+            value: "d\n",
+            is_raw: false,
+        },
+        14..16,
+    ),
+    (
+        Rbrace,
+        16..17,
+    ),
+    (
+        FStringMiddle {
+            value: "__",
+            is_raw: false,
+        },
+        17..19,
+    ),
+    (
+        FStringEnd,
+        19..22,
+    ),
+    (
+        FStringStart,
+        23..25,
+    ),
+    (
+        FStringMiddle {
+            value: "__",
+            is_raw: false,
+        },
+        25..27,
+    ),
+    (
+        Lbrace,
+        27..28,
+    ),
+    (
+        NonLogicalNewline,
+        28..29,
+    ),
+    (
+        Name {
+            name: "x",
+        },
+        33..34,
+    ),
+    (
+        Colon,
+        34..35,
+    ),
+    (
+        FStringMiddle {
+            value: "d",
+            is_raw: false,
+        },
+        35..36,
+    ),
+    (
+        NonLogicalNewline,
+        36..37,
+    ),
+    (
+        Rbrace,
+        37..38,
+    ),
+    (
+        FStringMiddle {
+            value: "__",
+            is_raw: false,
+        },
+        38..40,
+    ),
+    (
+        FStringEnd,
+        40..41,
+    ),
+    (
+        Newline,
+        41..41,
+    ),
+]