Incorrect f-string parsing (#112)

* Fix parse_fstring

* Add test

* Push char

* Remove unused import

ast/src/ranged.rs

@@ -1,7 +1,5 @@
 use crate::text_size::{TextRange, TextSize};
 
-pub use crate::builtin::*;
-
 pub trait Ranged {
     fn range(&self) -> TextRange;
 

parser/src/snapshots/rustpython_parser__string__tests__parse_fstring_escaped_brackets.snap

@@ -0,0 +1,15 @@
+---
+source: parser/src/string.rs
+expression: parse_ast
+---
+[
+    Constant(
+        ExprConstant {
+            range: 0..10,
+            value: Str(
+                "\\{x\\}",
+            ),
+            kind: None,
+        },
+    ),
+]

parser/src/string.rs

@@ -503,8 +503,12 @@ impl<'a> StringParser<'a> {
                 }
                 '\\' if !self.kind.is_raw() => {
                     self.next_char();
+                    if let Some('{' | '}') = self.peek() {
+                        content.push('\\');
+                    } else {
                         content.push_str(&self.parse_escaped_char()?);
                     }
+                }
                 _ => {
                     content.push(ch);
                     self.next_char();
@@ -956,6 +960,13 @@ mod tests {
         insta::assert_debug_snapshot!(parse_ast);
     }
 
+    #[test]
+    fn test_parse_fstring_escaped_brackets() {
+        let source = "\\{{x\\}}";
+        let parse_ast = parse_fstring(source).unwrap();
+        insta::assert_debug_snapshot!(parse_ast);
+    }
+
     #[test]
     fn test_parse_string_concat() {
         let source = "'Hello ' 'world'";