calculate features the hard way

Author: Eh2406

src/cargo/core/resolver/errors.rs

@@ -50,6 +50,7 @@ impl fmt::Display for ResolveError {
 
 pub type ActivateResult<T> = Result<T, ActivateError>;
 
+#[derive(Debug)]
 pub enum ActivateError {
     Fatal(failure::Error),
     Conflict(PackageId, ConflictReason),

src/cargo/core/resolver/mod.rs

@@ -160,18 +160,44 @@ pub fn resolve(
     // If we have a shell, emit warnings about required deps used as feature.
     if print_warnings && config.is_some() {
         let mut new_cx = cx.clone();
-        for (j, _) in cx.activations.values() {
-            if let Some(features) = cx.resolve_features.get(&j.package_id()) {
-                let features: Vec<_> = features.iter().cloned().collect();
-                let method = Method::Required {
-                    dev_deps: false,
-                    features: &features,
-                    all_features: false,
-                    uses_default_features: false,
-                };
-                let _ = new_cx.resolve_features(None, j, &method, config);
+        new_cx.resolve_features = im_rc::HashMap::new();
+        let mut features_from_dep = HashMap::new();
+        for (summery, method) in summaries {
+            for (dep, features) in new_cx
+                .resolve_features(None, summery, &method, config)
+                .expect("can not resolve_features for a required summery")
+            {
+                features_from_dep.insert((summery.package_id(), dep), features);
+            }
+        }
+        for summery in resolve.sort().iter().rev().map(|id| {
+            cx.activations
+                .get(&id.as_activations_key())
+                .expect("id in dependency graph but not in activations")
+                .0
+                .clone()
+        }) {
+            for (parent, deps) in cx.parents.edges(&summery.package_id()) {
+                for dep in deps.iter() {
+                    let features = features_from_dep
+                        .remove(&(*parent, dep.clone()))
+                        .expect("fulfilled a dep that was not needed");
+                    let method = Method::Required {
+                        dev_deps: false,
+                        features: &features,
+                        all_features: false,
+                        uses_default_features: dep.uses_default_features(),
+                    };
+                    for (dep, features) in new_cx
+                        .resolve_features(None, &summery, &method, config)
+                        .expect("can not resolve_features for a used dep")
+                    {
+                        features_from_dep.insert((summery.package_id(), dep), features);
+                    }
+                }
             }
         }
+        assert_eq!(cx.resolve_features, new_cx.resolve_features);
     }
 
     Ok(resolve)

tests/testsuite/support/resolver.rs

@@ -114,7 +114,7 @@ pub fn resolve_with_config_raw(
         &mut registry,
         &HashSet::new(),
         config,
-        false,
+        true,
         true,
     );