Fix replacing with embedded newline characters

Resolves #39

babi/file.py

@@ -464,8 +464,27 @@ class File:
                 with self.edit_action_context('replace', final=True):
                     replaced = match.expand(replace)
                     line = screen.file.lines[line_y]
-                    line = line[:match.start()] + replaced + line[match.end():]
+                    if '\n' in replaced:
-                    screen.file.lines[line_y] = line
+                        replaced_lines = replaced.split('\n')
+                        self.lines[line_y] = (
+                            f'{line[:match.start()]}{replaced_lines[0]}'
+                        )
+                        for i, ins_line in enumerate(replaced_lines[1:-1], 1):
+                            self.lines.insert(line_y + i, ins_line)
+                        last_insert = line_y + len(replaced_lines) - 1
+                        self.lines.insert(
+                            last_insert,
+                            f'{replaced_lines[-1]}{line[match.end():]}',
+                        )
+                        self.y = last_insert
+                        self.x = self.x_hint = 0
+                        search.offset = len(replaced_lines[-1])
+                    else:
+                        self.lines[line_y] = (
+                            f'{line[:match.start()]}'
+                            f'{replaced}'
+                            f'{line[match.end():]}'
+                        )
                         search.offset = len(replaced)
             elif res == 'n':
                 search.offset = 1

tests/features/replace_test.py

@@ -272,3 +272,31 @@ def test_replace_separate_line_after_wrapping(run, ten_lines):
         h.await_text_missing('line_0')
         h.press('y')
         h.await_text_missing('line_1')
+
+
+def test_replace_with_newline_characters(run, ten_lines):
+    with run(str(ten_lines)) as h, and_exit(h):
+        h.press('^\\')
+        h.await_text('search (to replace):')
+        h.press_and_enter('(line)_([01])')
+        h.await_text('replace with:')
+        h.press_and_enter(r'\1\n\2')
+        h.await_text('replace [yes, no, all]?')
+        h.press('a')
+        h.await_text_missing('line_0')
+        h.await_text_missing('line_1')
+        h.await_text('line\n0\nline\n1\n')
+
+
+def test_replace_with_multiple_newline_characters(run, ten_lines):
+    with run(str(ten_lines)) as h, and_exit(h):
+        h.press('^\\')
+        h.await_text('search (to replace):')
+        h.press_and_enter('(li)(ne)_(1)')
+        h.await_text('replace with:')
+        h.press_and_enter(r'\1\n\2\n\3\n')
+        h.await_text('replace [yes, no, all]?')
+        h.press('a')
+
+        h.await_text_missing('line_1')
+        h.await_text('li\nne\n1\n\nline_2')