Auto merge of #8194 - sunshowers:activate, r=ehuss

features: allow activated_features_unverified to communicate not-present

Hi there! :)

I'm currently writing [`cargo-guppy`](https://github.com/facebookincubator/cargo-guppy), a toolkit for analyzing Rust dependency graphs. As part of that I'm writing some tests to compare guppy to `cargo` (see facebookarchive/cargo-guppy#126), to ensure that it produces the same results for the subset of analyses `cargo` can do.

While writing tests I found it useful to distinguish between packages that weren't present at all and packages that were activated but with no features. This commit adds that functionality to the `_unverified` method.

(BTW, of possible interest to @ehuss, I've also found some interesting behavior differences between the v1 and v2 resolvers. Will file issues for them soon!)

src/cargo/core/resolver/features.rs

@@ -208,36 +208,34 @@ impl ResolvedFeatures {
         pkg_id: PackageId,
         features_for: FeaturesFor,
     ) -> Vec<InternedString> {
-        self.activated_features_int(pkg_id, features_for, true)
+        self.activated_features_int(pkg_id, features_for)
+            .expect("activated_features for invalid package")
     }
 
-    /// Variant of `activated_features` that returns an empty Vec if this is
+    /// Variant of `activated_features` that returns `None` if this is
     /// not a valid pkg_id/is_build combination. Used in places which do
     /// not know which packages are activated (like `cargo clean`).
     pub fn activated_features_unverified(
         &self,
         pkg_id: PackageId,
         features_for: FeaturesFor,
-    ) -> Vec<InternedString> {
-        self.activated_features_int(pkg_id, features_for, false)
+    ) -> Option<Vec<InternedString>> {
+        self.activated_features_int(pkg_id, features_for).ok()
     }
 
     fn activated_features_int(
         &self,
         pkg_id: PackageId,
         features_for: FeaturesFor,
-        verify: bool,
-    ) -> Vec<InternedString> {
+    ) -> CargoResult<Vec<InternedString>> {
         if let Some(legacy) = &self.legacy {
-            legacy.get(&pkg_id).map_or_else(Vec::new, |v| v.clone())
+            Ok(legacy.get(&pkg_id).map_or_else(Vec::new, |v| v.clone()))
         } else {
             let is_build = self.opts.decouple_host_deps && features_for == FeaturesFor::HostDep;
             if let Some(fs) = self.activated_features.get(&(pkg_id, is_build)) {
-                fs.iter().cloned().collect()
-            } else if verify {
-                panic!("features did not find {:?} {:?}", pkg_id, is_build)
+                Ok(fs.iter().cloned().collect())
             } else {
-                Vec::new()
+                anyhow::bail!("features did not find {:?} {:?}", pkg_id, is_build)
             }
         }
     }

src/cargo/ops/cargo_clean.rs

@@ -129,8 +129,9 @@ pub fn clean(ws: &Workspace<'_>, opts: &CleanOptions<'_>) -> CargoResult<()> {
                         // Use unverified here since this is being more
                         // exhaustive than what is actually needed.
                         let features_for = unit_for.map_to_features_for();
-                        let features =
-                            features.activated_features_unverified(pkg.package_id(), features_for);
+                        let features = features
+                            .activated_features_unverified(pkg.package_id(), features_for)
+                            .unwrap_or_default();
                         units.push(interner.intern(
                             pkg, target, profile, *kind, *mode, features, /*is_std*/ false,
                         ));

src/cargo/ops/cargo_compile.rs

@@ -978,7 +978,10 @@ pub fn resolve_all_features(
             .proc_macro();
         for dep in deps {
             let features_for = FeaturesFor::from_for_host(is_proc_macro || dep.is_build());
-            for feature in resolved_features.activated_features_unverified(dep_id, features_for) {
+            for feature in resolved_features
+                .activated_features_unverified(dep_id, features_for)
+                .unwrap_or_default()
+            {
                 features.insert(format!("{}/{}", dep.name_in_toml(), feature));
             }
         }