Fix requirements-txt-fixer reordering --index-url after --extra-index-url (#612)

pre_commit_hooks/requirements_txt_fixer.py

@@ -50,6 +50,21 @@ def __lt__(self, requirement: Requirement) -> bool:
             # with comments is kept)
             if self.name == requirement.name:
                 return bool(self.comments) > bool(requirement.comments)
+            # `--index-url` must be ordered before `--extra-index-url`.  pip
+            # uses the first `--index-url` as the primary index and treats
+            # subsequent `--extra-index-url` entries as additional indexes; if
+            # `--extra-index-url` appears first it is silently dropped, so we
+            # keep the index URL first (see issue #612).
+            if (
+                    self.name == b'--index-url' and
+                    requirement.name == b'--extra-index-url'
+            ):
+                return True
+            if (
+                    self.name == b'--extra-index-url' and
+                    requirement.name == b'--index-url'
+            ):
+                return False
             return self.name < requirement.name
 
     def is_complete(self) -> bool:

tests/requirements_txt_fixer_test.py

@@ -107,6 +107,26 @@
             PASS,
             b'a=2.0.0 \\\n --hash=sha256:abcd\nb==1.0.0\n',
         ),
+        # `--index-url` must be kept before `--extra-index-url` so pip does
+        # not drop the primary index URL (see issue #612).
+        (
+            b'--index-url https://primary.example.com\n'
+            b'--extra-index-url https://extra.example.com\n'
+            b'foo==1.0\n',
+            PASS,
+            b'--index-url https://primary.example.com\n'
+            b'--extra-index-url https://extra.example.com\n'
+            b'foo==1.0\n',
+        ),
+        (
+            b'--extra-index-url https://extra.example.com\n'
+            b'--index-url https://primary.example.com\n'
+            b'foo==1.0\n',
+            FAIL,
+            b'--index-url https://primary.example.com\n'
+            b'--extra-index-url https://extra.example.com\n'
+            b'foo==1.0\n',
+        ),
     ),
 )
 def test_integration(input_s, expected_retval, output, tmpdir):