fix: don't remove double braces in f-strings in rule directives [closes

#207]

snakefmt/parser/syntax.py

@@ -1,6 +1,7 @@
 """
 Code in charge of parsing and validating Snakemake syntax
 """
+import sys
 import tokenize
 from abc import ABC, abstractmethod
 from re import match as re_match
@@ -329,9 +330,17 @@ def in_brackets(self):
     def parse_params(self, snakefile: TokenIterator):
         cur_param = Parameter(self.token)
         prev_token = None
-
         while True:
             cur_param = self.process_token(cur_param, prev_token)
+            if (
+                self.token is not None
+                and sys.version_info >= (3, 12)
+                and self.token.type == tokenize.FSTRING_MIDDLE
+            ):
+                if self.token.string.endswith("}"):
+                    cur_param.value += "}"
+                elif self.token.string.endswith("{"):
+                    cur_param.value += "{"
             try:
                 prev_token = self.token
                 self.token = next(snakefile)

tests/test_formatter.py

@@ -845,6 +845,23 @@ def test_tpq_inside_run_block(self):
 
         assert formatter.get_formatted() == snakecode
 
+    def test_f_string_with_double_braces_in_input(self):
+        """rule align:
+        input:
+            sequences="results/{build_name}/filtered.fasta",
+        params:
+            translation_template=lambda w: f"{w.build_name}/{{cds}}.fasta","""
+        snakecode = (
+            "rule align:\n"
+            f"{TAB * 1}input:\n"
+            f'{TAB * 2}sequences="results/{{build_name}}/filtered.fasta",\n'
+            f"{TAB * 1}params:\n"
+            f"{TAB * 2}"
+            + 'translation_template=lambda w: f"{w.build_name}/{{cds}}.fasta",\n'
+        )
+        formatter = setup_formatter(snakecode)
+        assert formatter.get_formatted() == snakecode
+
 
 class TestReformatting_SMK_BREAK:
     """