Merge pull request #2488 from PyCQA/copilot/fix-isort-empty-comments

Fix: preserve bare `#` inline comments on imports

Author: DanielNoord

isort/comments.py

@@ -1,12 +1,15 @@
-def parse(line: str) -> tuple[str, str]:
+def parse(line: str) -> tuple[str, str | None]:
     """Parses import lines for comments and returns back the
     import statement and the associated comment.
+
+    Returns ``None`` as the comment when no ``#`` is present in the line,
+    and an empty string when a bare ``#`` with no text is present.
     """
     comment_start = line.find("#")
     if comment_start != -1:
         return (line[:comment_start], line[comment_start + 1 :].strip())
 
-    return (line, "")
+    return (line, None)
 
 
 def add_to_line(
@@ -26,4 +29,7 @@ def add_to_line(
     for comment in comments:
         if comment not in unique_comments:
             unique_comments.append(comment)
-    return f"{parse(original_string)[0]}{comment_prefix} {'; '.join(unique_comments)}"
+    comment_text = "; ".join(unique_comments)
+    if comment_text:
+        return f"{parse(original_string)[0]}{comment_prefix} {comment_text}"
+    return f"{parse(original_string)[0]}{comment_prefix}"

isort/output.py

@@ -340,9 +340,10 @@ def _with_from_imports(
                     comment = (
                         parsed.categorized_comments["nested"].get(module, {}).pop(from_import, None)
                     )
-                    if comment:
+                    if comment is not None:
+                        comment_text = f" {comment}" if comment else ""
                         single_import_line += (
-                            f"{(comments and ';') or config.comment_prefix} {comment}"
+                            f"{(comments and ';') or config.comment_prefix}{comment_text}"
                         )
                     if from_import in as_imports:
                         if (
@@ -410,7 +411,7 @@ def _with_from_imports(
                             .get(module, {})
                             .pop(from_import, None)
                         )
-                        if specific_comment:
+                        if specific_comment is not None:
                             from_comments.append(specific_comment)
                         output.append(
                             wrap.line(
@@ -432,7 +433,7 @@ def _with_from_imports(
                             .get(module, {})
                             .pop(as_import, None)
                         )
-                        if specific_comment:
+                        if specific_comment is not None:
                             from_comments.append(specific_comment)
 
                         output.append(
@@ -465,7 +466,7 @@ def _with_from_imports(
                     comment = (
                         parsed.categorized_comments["nested"].get(module, {}).pop(from_import, None)
                     )
-                    if comment:
+                    if comment is not None:
                         # If the comment is a noqa and hanging indent wrapping is used,
                         # keep the name in the main list and hoist the comment to the statement.
                         if (
@@ -488,8 +489,9 @@ def _with_from_imports(
                             removed=config.ignore_comments,
                             comment_prefix=config.comment_prefix,
                         )
+                        comment_text = f" {comment}" if comment else ""
                         single_import_line += (
-                            f"{(use_comments and ';') or config.comment_prefix} {comment}"
+                            f"{(use_comments and ';') or config.comment_prefix}{comment_text}"
                         )
                         output.append(wrap.line(single_import_line, parsed.line_separator, config))
 
@@ -610,17 +612,17 @@ def _with_straight_imports(
                 inline_comments.extend(parsed.categorized_comments["straight"][module])
 
         combined_straight_imports = ", ".join(straight_modules)
-        if inline_comments:
-            combined_inline_comments = " ".join(inline_comments)
-        else:
-            combined_inline_comments = ""
 
         output.extend(above_comments)
 
-        if combined_inline_comments:
-            output.append(
-                f"{import_type} {combined_straight_imports}  # {combined_inline_comments}"
-            )
+        if inline_comments:
+            combined_inline_comments = " ".join(c for c in inline_comments if c)
+            if combined_inline_comments:
+                output.append(
+                    f"{import_type} {combined_straight_imports}  # {combined_inline_comments}"
+                )
+            else:
+                output.append(f"{import_type} {combined_straight_imports}  #")
         else:
             output.append(f"{import_type} {combined_straight_imports}")
 

isort/parse.py

@@ -189,7 +189,7 @@ def file_contents(contents: str, config: Config = DEFAULT_CONFIG) -> ParsedConte
                 import_index = index - 1
             nested_comments = {}
             import_string, comment = parse_comments(line)
-            comments = [comment] if comment else []
+            comments = [comment] if comment is not None else []
             line_parts = [part for part in strip_syntax(import_string).strip().split(" ") if part]
             if type_of_import == "from" and len(line_parts) == 2 and comments:
                 nested_comments[line_parts[-1]] = comments[0]
@@ -208,7 +208,7 @@ def _get_next_line() -> tuple[str, str | None]:
             for extra_line in extra_lines:
                 raw_lines.append(extra_line.line)
                 # If during parsing of the continuation lines we encounter a comment, we record it.
-                if extra_line.comment:
+                if extra_line.comment is not None:
                     comments.append(extra_line.comment)
                     stripped_line = strip_syntax(extra_line.line).strip()
                     if (
@@ -253,7 +253,7 @@ def _get_next_line() -> tuple[str, str | None]:
 
                         full_name = f"{nested_module} as {as_name}"
                         associated_comment = nested_comments.get(full_name)
-                        if associated_comment:
+                        if associated_comment is not None:
                             categorized_comments["nested"].setdefault(top_level_module, {})[
                                 full_name
                             ] = associated_comment
@@ -308,7 +308,7 @@ def _get_next_line() -> tuple[str, str | None]:
                 root = imports[placed_module][type_of_import]
                 for import_name in just_imports:
                     associated_comment = nested_comments.get(import_name)
-                    if associated_comment:
+                    if associated_comment is not None:
                         categorized_comments["nested"].setdefault(import_from, {})[import_name] = (
                             associated_comment
                         )

tests/unit/test_ticketed_features.py

@@ -1195,3 +1195,22 @@ def test_sort_separate_packages_issue_2104():
 from package2 import bar
 """
     )
+
+
+def test_isort_preserves_empty_inline_comments() -> None:
+    """isort should not strip empty inline comments (bare `#`).
+    See: https://github.com/PyCQA/isort/issues/1913
+    """
+    # Straight imports
+    assert isort.code("import a  #\n") == "import a  #\n"
+
+    # From imports
+    assert isort.code("from foo import bar  #\n") == "from foo import bar  #\n"
+
+    # Should be idempotent
+    assert isort.code(isort.code("import a  #\n")) == "import a  #\n"
+    assert isort.code(isort.code("from foo import bar  #\n")) == "from foo import bar  #\n"
+
+    # Regular (non-empty) comments should still work
+    assert isort.code("import a  # comment\n") == "import a  # comment\n"
+    assert isort.code("from foo import bar  # comment\n") == "from foo import bar  # comment\n"