Fix template whitespace collapse merging lines on trailing whitespace

src/outlines/templates.py

@@ -137,7 +137,7 @@ def build_template_from_string(
     # Remove extra whitespaces, except those that immediately follow a newline symbol.
     # This is necessary to avoid introducing whitespaces after backslash `\` characters
     # used to continue to the next line without linebreak.
-    cleaned_template = re.sub(r"(?![\r\n])(\b\s+)", " ", cleaned_template)
+    cleaned_template = re.sub(r"(?![\r\n])(\b[^\S\r\n]+)", " ", cleaned_template)
 
     env = create_jinja_env(None, filters)
 

tests/test_templates.py

@@ -397,3 +397,13 @@ def test_get_schema():
     assert pydantic_nested_schema_output == (
         '{\n  "name": "<name>",\n  "inner": {\n    "foo": "<foo>"\n  }\n}'
     )
+
+
+def test_render_trailing_whitespace_preserves_linebreak():
+    # A trailing space before a newline must not swallow the line break.
+    assert build_template_from_string("foo   \nbar").render() == "foo \nbar"
+
+
+def test_render_trailing_whitespace_keeps_next_line_indentation():
+    src = "\n    A test line \n        An indented line\n    "
+    assert build_template_from_string(src).render() == "A test line \n    An indented line"