From 6ac179a14662f606530ecc46965b52cfc66f6ece Mon Sep 17 00:00:00 2001
From: Timothy Crosley <timothy.crosley@gmail.com>
Date: Thu, 3 Sep 2020 20:36:03 -0700
Subject: [PATCH] Fix issue #1454: Endless import sorting for indendent imports
 with section heading and preceding comment.

---
 isort/core.py                  | 15 +++++++++------
 tests/unit/test_regressions.py | 23 +++++++++++++++++++++++
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/isort/core.py b/isort/core.py
index 08adc239c..f3197b99d 100644
--- a/isort/core.py
+++ b/isort/core.py
@@ -58,7 +58,6 @@ def process(
     contains_imports: bool = False
     in_top_comment: bool = False
     first_import_section: bool = True
-    section_comments = [f"# {heading}" for heading in config.import_headings.values()]
     indent: str = ""
     isort_off: bool = False
     code_sorting: Union[bool, str] = False
@@ -146,11 +145,11 @@ def process(
             if (
                 (index == 0 or (index in (1, 2) and not contains_imports))
                 and stripped_line.startswith("#")
-                and stripped_line not in section_comments
+                and stripped_line not in config.section_comments
             ):
                 in_top_comment = True
             elif in_top_comment:
-                if not line.startswith("#") or stripped_line in section_comments:
+                if not line.startswith("#") or stripped_line in config.section_comments:
                     in_top_comment = False
                     first_comment_index_end = index - 1
 
@@ -210,8 +209,13 @@ def process(
                     else:
                         code_sorting_section += line
                         line = ""
-                elif stripped_line in config.section_comments and not import_section:
-                    import_section += line
+                elif stripped_line in config.section_comments:
+                    if import_section and not contains_imports:
+                        output_stream.write(import_section)
+                        import_section = line
+                        not_imports = False
+                    else:
+                        import_section += line
                     indent = line[: -len(line.lstrip())]
                 elif not (stripped_line or contains_imports):
                     not_imports = True
@@ -337,7 +341,6 @@ def process(
                             line_separator=line_separator,
                             ignore_whitespace=config.ignore_whitespace,
                         )
-
                         output_stream.write(sorted_import_section)
                         if not line and not indent and next_import_section:
                             output_stream.write(line_separator)
diff --git a/tests/unit/test_regressions.py b/tests/unit/test_regressions.py
index 5feaef6fb..752adc343 100644
--- a/tests/unit/test_regressions.py
+++ b/tests/unit/test_regressions.py
@@ -926,3 +926,26 @@ def test_empty_float_to_top_shouldnt_error_issue_1453():
 """,
         show_diff=True,
     )
+
+
+def test_import_sorting_shouldnt_be_endless_with_headers_issue_1454():
+    """isort should never enter an endless sorting loop.
+    See: https://github.com/PyCQA/isort/issues/1454
+    """
+    assert isort.check_code(
+        """
+
+# standard library imports
+import sys
+
+try:
+    # Comment about local lib
+    # related third party imports
+    from local_lib import stuff
+except ImportError as e:
+    pass
+""",
+        known_third_party=["local_lib"],
+        import_heading_thirdparty="related third party imports",
+        show_diff=True,
+    )