fix: preserve from_body comments on as-only emit paths

Fold single-line body comments via with_comments instead of orphan
indented lines, and drain remaining body comments onto the last emitted
statement when no grouped import_statement is built.

Signed-off-by: Alex Chen <l46983284@gmail.com>

Author: alexchen-sys

isort/output.py

@@ -288,13 +288,20 @@ def _inject_from_body_comments(
     body_comments: list[str],
     line_separator: str,
     indent: str,
+    *,
+    comment_prefix: str,
+    ignore_comments: bool = False,
 ) -> str:
     """Re-insert comment-only lines inside a multi-line from-import statement.
 
     Comment-only members of a parenthesised import group must stay as their own
     indented lines.  Collapsing them onto the opening ``import (`` line produces
     a single long ``# a,; b,; c`` comment that breaks line-length checkers.
     See issue #1852.
+
+    When the statement is single-line (no closing ``)``), fold the body comments
+    onto that statement with ``with_comments`` instead of emitting orphan
+    indented comment lines. Orphan lines are non-idempotent under a second sort.
     """
     if not body_comments:
         return import_statement
@@ -312,9 +319,13 @@ def _inject_from_body_comments(
             lines[index:index] = comment_lines
             return line_separator.join(lines)
 
-    # Fallback for single-line / non-parenthesised output: keep comments after
-    # the import statement rather than dropping them.
-    return line_separator.join([import_statement, *comment_lines])
+    # Single-line / no-paren fallback: main-compatible fold onto the statement.
+    return with_comments(
+        body_comments,
+        import_statement,
+        removed=ignore_comments,
+        comment_prefix=comment_prefix,
+    )
 
 
 # Ignore DeepSource cyclomatic complexity check for this function. It was
@@ -756,9 +767,24 @@ def _with_from_imports(
                         body_comments,
                         parsed.line_separator,
                         config.indent,
+                        comment_prefix=config.comment_prefix,
+                        ignore_comments=config.ignore_comments,
                     )
                     body_comments = []
                 output.append(import_statement)
+            elif body_comments and not config.ignore_comments and output:
+                # as-import-only / nested-only paths may emit lines without a final
+                # grouped import_statement. Never drop body comments: fold them onto
+                # the last statement emitted for this module.
+                output[-1] = _inject_from_body_comments(
+                    output[-1],
+                    body_comments,
+                    parsed.line_separator,
+                    config.indent,
+                    comment_prefix=config.comment_prefix,
+                    ignore_comments=config.ignore_comments,
+                )
+                body_comments = []
     return output
 
 

tests/unit/test_regressions.py

@@ -2495,18 +2495,45 @@ def test_combine_star_folds_body_comments_issue_1852():
 
 
 def test_inject_from_body_comments_branches_issue_1852():
-    """The helper retains empty comments and has a lossless single-line fallback."""
-    assert _inject_from_body_comments("from foo import alpha", [], "\n", "    ") == (
-        "from foo import alpha"
-    )
-    assert _inject_from_body_comments("from foo import alpha", ["disabled", ""], "\n", "    ") == (
-        "from foo import alpha\n    # disabled\n    #"
-    )
+    """Paren form keeps body lines; single-line form folds via with_comments."""
+    assert _inject_from_body_comments(
+        "from foo import alpha", [], "\n", "    ", comment_prefix="  #"
+    ) == ("from foo import alpha")
     assert _inject_from_body_comments(
-        "from foo import (\n    alpha,\n)", ["disabled", ""], "\n", "    "
+        "from foo import alpha", ["disabled", ""], "\n", "    ", comment_prefix="  #"
+    ) == ("from foo import alpha  # disabled; ")
+    assert _inject_from_body_comments(
+        "from foo import (\n    alpha,\n)",
+        ["disabled", ""],
+        "\n",
+        "    ",
+        comment_prefix="  #",
     ) == ("from foo import (\n    alpha,\n    # disabled\n    #\n)")
 
 
+def test_as_import_only_body_comment_preserved_issue_1852():
+    """as-import-only groups must not drop comment-only body members."""
+    to_sort = "from foo import (\n    alpha as a,\n    # disabled\n)\n"
+    expected = "from foo import alpha as a  # disabled\n"
+    first = isort.code(to_sort, profile="black")
+    assert first == expected
+    assert isort.code(first, profile="black") == first
+
+
+def test_mixed_as_and_live_body_comment_preserved_issue_1852():
+    """Body comments survive when as-imports emit before remaining live names."""
+    to_sort = "from foo import (\n    alpha as a,\n    # disabled\n    beta,\n)\n"
+    first = isort.code(to_sort, profile="black")
+    assert "# disabled" in first
+    assert "alpha as a" in first
+    assert "beta" in first
+    for line in first.splitlines():
+        if line.startswith("    #"):
+            assert "(" in first
+            assert ")" in first
+    assert isort.code(first, profile="black") == first
+
+
 def test_combine_star_folds_body_comments_when_comments_are_enabled_issue_1852(monkeypatch):
     """combine_star folds body comments only when comments are retained."""
     parsed = parse.file_contents(