Support '--use-feature' in requirements files

news/8601.feature

@@ -0,0 +1 @@
+Support ``--use-feature`` in requirements files

src/pip/_internal/operations/freeze.py

@@ -100,7 +100,8 @@ def freeze(
                                 '--pre',
                                 '--trusted-host',
                                 '--process-dependency-links',
-                                '--extra-index-url'))):
+                                '--extra-index-url',
+                                '--use-feature'))):
                         line = line.rstrip()
                         if line not in emitted_options:
                             emitted_options.add(line)

src/pip/_internal/req/req_file.py

@@ -62,6 +62,7 @@
     cmdoptions.require_hashes,
     cmdoptions.pre,
     cmdoptions.trusted_host,
+    cmdoptions.use_new_feature,
 ]  # type: List[Callable[..., optparse.Option]]
 
 # options to be passed to requirements
@@ -224,12 +225,18 @@ def handle_option_line(
 ):
     # type:  (...) -> None
 
-    # percolate hash-checking option upward
-    if options and opts.require_hashes:
-        options.require_hashes = opts.require_hashes
+    if options:
+        # percolate options upward
+        if opts.require_hashes:
+            options.require_hashes = opts.require_hashes
+        if opts.features_enabled:
+            options.features_enabled.extend(
+                f for f in opts.features_enabled
+                if f not in options.features_enabled
+            )
 
     # set finder options
-    elif finder:
+    if finder:
         find_links = finder.find_links
         index_urls = finder.index_urls
         if opts.index_url:

tests/functional/test_freeze.py

@@ -548,6 +548,7 @@ def test_freeze_nested_vcs(script, outer_vcs, inner_vcs):
     --extra-index-url http://ignore
     --find-links http://ignore
     --index-url http://ignore
+    --use-feature 2020-resolver
 """)
 
 

tests/unit/test_req_file.py

@@ -47,6 +47,7 @@ def options(session):
         isolated_mode=False,
         index_url='default_url',
         format_control=FormatControl(set(), set()),
+        features_enabled=[],
     )
 
 
@@ -382,6 +383,13 @@ def test_set_finder_allow_all_prereleases(self, line_processor, finder):
         line_processor("--pre", "file", 1, finder=finder)
         assert finder.allow_all_prereleases
 
+    def test_use_feature(self, line_processor, options):
+        """--use-feature can be set in requirements files."""
+        line_processor(
+            "--use-feature=2020-resolver", "filename", 1, options=options
+        )
+        assert "2020-resolver" in options.features_enabled
+
     def test_relative_local_find_links(
         self, line_processor, finder, monkeypatch, tmpdir
     ):