Fix escaped newline handling

src/flynt/code_editor.py

@@ -20,6 +20,7 @@
 from flynt.utils.utils import (
     apply_unicode_escape_map,
     contains_comment,
+    preserve_escaped_newlines,
     unicode_escape_map,
 )
 
@@ -176,6 +177,7 @@ def try_chunk(self, chunk: AstChunk) -> None:
         if changed and escape_map and not is_raw:
             converted = apply_unicode_escape_map(converted, escape_map)
         if changed:
+            converted = preserve_escaped_newlines(snippet, converted)
             contract_lines = chunk.n_lines - 1
             if contract_lines == 0:
                 line = self.src_lines[chunk.start_line]
@@ -218,7 +220,9 @@ def maybe_replace(
                     - self._byte_to_char_idx(chunk.start_line, chunk.start_idx)
                     for line in lines
                 )
-                converted = converted.replace("\\n", "\n")
+                snippet_text = self.code_in_chunk(chunk)
+                if "\\n" not in snippet_text:
+                    converted = converted.replace("\\n", "\n")
             else:
                 lines_fit = len(
                     f"{converted}{rest}"

src/flynt/utils/utils.py

@@ -209,3 +209,30 @@ def repl(match: re.Match[str]) -> str:
 def contains_unicode_escape(code: str) -> bool:
     """Return ``True`` if ``code`` contains unicode or octal escape sequences."""
     return bool(unicode_escape_re.search(code))
+
+
+def preserve_escaped_newlines(original: str, converted: str) -> str:
+    """Restore backslash newline escapes lost during AST transformation."""
+    orig_lines = original.splitlines()
+    conv_lines = converted.splitlines()
+    if not orig_lines or not conv_lines:
+        return converted
+    if orig_lines[0].rstrip().endswith("\\") and not conv_lines[0].rstrip().endswith(
+        "\\"
+    ):
+        m = re.match(r"(\s*[furbFURB]*[\'\"]{3})", conv_lines[0])
+        if m:
+            prefix = m.group(1)
+            rest = conv_lines[0][len(prefix) :].lstrip()
+            if len(orig_lines) > 1:
+                indent = len(orig_lines[1]) - len(orig_lines[1].lstrip())
+            else:
+                indent = len(prefix) - len(prefix.lstrip())
+            conv_lines[0] = prefix + "\\"
+            if rest:
+                conv_lines.insert(1, " " * indent + rest)
+    for idx, line in enumerate(orig_lines[1:], start=1):
+        if line.strip() == "\\":
+            indent = len(line) - len(line.lstrip())
+            conv_lines.insert(idx, " " * indent + "\\")
+    return "\n".join(conv_lines)

test/integration/expected_out_single_line/escaped_newline.py

@@ -0,0 +1,31 @@
+from textwrap import dedent
+
+def f():
+    arg = "text"
+    return dedent(
+        """\
+        \
+        some {}
+        lorem ipsum
+        """.format(arg)
+    )
+
+
+def f_extra():
+    arg = "text"
+    return """\
+    some {}\n""".format(arg)
+
+
+def f_multiple():
+    arg = "text"
+    return """\
+    \
+    \
+    some {}\n""".format(arg)
+
+
+def f_single_quotes():
+    arg = "text"
+    return '''\
+    some {}\n'''.format(arg)

test/integration/test_issue83.py

@@ -1,11 +1,9 @@
-import pytest
 from functools import partial
 
 from test.integration.utils import try_on_file
 from flynt.code_editor import fstringify_code_by_line
 
 
-@pytest.mark.xfail(reason="newline escapes lost, issue #83")
 def test_escaped_newline(state):
     out, expected = try_on_file(
         "escaped_newline.py",

test/integration/utils.py

@@ -6,7 +6,6 @@
 EXCLUDED = {
     "bom.py",
     "class.py",
-    "escaped_newline.py",  # not supported yet, #83 on github
     "multiline_limit.py",
 }
 samples = {p.name for p in (int_test_path / "samples_in").glob("*.py")} - EXCLUDED