Deprecate legacy install when --no-binary is used

Author: sbidoul

src/pip/_internal/req/req_install.py

@@ -822,6 +822,18 @@ def install(
             self.install_succeeded = True
             return
 
+        if self.legacy_install_reason == 81020:  # TODO issue id
+            deprecated(
+                reason=(
+                    "Installing {} using the legacy 'setup.py install' "
+                    "method, due to binaries being disabled for it.".
+                    format(self.name)
+                ),
+                replacement="--use-feature=always-install-via-wheel",
+                gone_in=None,
+                issue=81020,  # TODO issue id
+            )
+
         # TODO: Why don't we do this for editable installs?
 
         # Extend the list of global and install options passed on to

src/pip/_internal/wheel_builder.py

@@ -72,10 +72,7 @@ def _should_build(
         return True
 
     if not check_binary_allowed(req):
-        logger.info(
-            "Using legacy 'setup.py install' for %s, due to binaries "
-            "being disabled for it.", req.name,
-        )
+        req.legacy_install_reason = 81020  # TODO issue id
         return False
 
     if not is_wheel_installed():