Allow --prefer-binary option in requirements file

news/7693.feature

@@ -0,0 +1 @@
+Allow specifying --prefer-binary option in a requirements file

src/pip/_internal/build_env.py

@@ -193,6 +193,8 @@ class BuildEnvironment(object):
             args.extend(['--trusted-host', host])
         if finder.allow_all_prereleases:
             args.append('--pre')
+        if finder.prefer_binary:
+            args.append('--prefer-binary')
         args.append('--')
         args.extend(requirements)
         with open_spinner(message) as spinner:

src/pip/_internal/index/package_finder.py

@@ -693,6 +693,15 @@ class PackageFinder(object):
         # type: () -> None
         self._candidate_prefs.allow_all_prereleases = True
 
+    @property
+    def prefer_binary(self):
+        # type: () -> bool
+        return self._candidate_prefs.prefer_binary
+
+    def set_prefer_binary(self):
+        # type: () -> None
+        self._candidate_prefs.prefer_binary = True
+
     def make_link_evaluator(self, project_name):
         # type: (str) -> LinkEvaluator
         canonical_name = canonicalize_name(project_name)

src/pip/_internal/req/req_file.py

@@ -60,6 +60,7 @@ SUPPORTED_OPTIONS = [
     cmdoptions.find_links,
     cmdoptions.no_binary,
     cmdoptions.only_binary,
+    cmdoptions.prefer_binary,
     cmdoptions.require_hashes,
     cmdoptions.pre,
     cmdoptions.trusted_host,
@@ -260,6 +261,9 @@ def handle_option_line(
         if opts.pre:
             finder.set_allow_all_prereleases()
 
+        if opts.prefer_binary:
+            finder.set_prefer_binary()
+
         if session:
             for host in opts.trusted_hosts or []:
                 source = 'line {} of {}'.format(lineno, filename)