Add support for sections in requirements-fixer

pre_commit_hooks/requirements_txt_fixer.py

@@ -66,10 +66,7 @@ class Requirement:
 
 
 def fix_requirements(f: IO[bytes]) -> int:
-    requirements: list[Requirement] = []
     before = list(f)
-    after: list[bytes] = []
-
     before_string = b''.join(before)
 
     # adds new line in case one is missing
@@ -81,17 +78,21 @@ def fix_requirements(f: IO[bytes]) -> int:
     if before_string.strip() == b'':
         return PASS
 
+    # split requirements into sections based on newlines
+    sections: list[list[Requirement]] = [[]]
+
     for line in before:
+        requirements = sections[-1]
+
         # If the most recent requirement object has a value, then it's
         # time to start building the next requirement object.
-
         if not len(requirements) or requirements[-1].is_complete():
             requirements.append(Requirement())
 
         requirement = requirements[-1]
 
         # If we see a newline before any requirements, then this is a
-        # top of file comment.
+        # top of section comment.
         if len(requirements) == 1 and line.strip() == b'':
             if (
                     len(requirement.comments) and
@@ -100,12 +101,22 @@ def fix_requirements(f: IO[bytes]) -> int:
                 requirement.value = b'\n'
             else:
                 requirement.comments.append(line)
+        elif line.lstrip() == b'':
+            sections.append([])
         elif line.lstrip().startswith(b'#') or line.strip() == b'':
             requirement.comments.append(line)
         else:
             requirement.append_value(line)
 
-    # if a file ends in a comment, preserve it at the end
+    after_string = b''
+
+    for requirements in sections:
+        after: list[bytes] = []
+
+        if len(after_string) > 0:
+            after_string += b'\n'
+
+        # if a section ends in a comment, preserve it at the end
         if requirements[-1].value is None:
             rest = requirements.pop().comments
         else:
@@ -131,7 +142,7 @@ def fix_requirements(f: IO[bytes]) -> int:
                 prev = requirement
         after.extend(rest)
 
-    after_string = b''.join(after)
+        after_string += b''.join(after)
 
     if before_string == after_string:
         return PASS

tests/requirements_txt_fixer_test.py

@@ -107,6 +107,25 @@ from pre_commit_hooks.requirements_txt_fixer import Requirement
             PASS,
             b'a=2.0.0 \\\n --hash=sha256:abcd\nb==1.0.0\n',
         ),
+        (
+            (
+                b'-c external.txt\n'
+                b'\n'
+                b'Peach\n'
+                b'apple\n'
+                b'banana\n'
+                b'pear\n'
+            ),
+            FAIL,
+            (
+                b'-c external.txt\n'
+                b'\n'
+                b'apple\n'
+                b'banana\n'
+                b'Peach\n'
+                b'pear\n'
+            ),
+        ),
     ),
 )
 def test_integration(input_s, expected_retval, output, tmpdir):