Fix resolve error with cyclic dev-dependency features.

There is a convoluted situation where a cyclic dev-dependency attempts
to enable a feature on its parent. It would result in a confusing error
saying a package didn't have a feature.

This check was intended only for CLI features, not features passed
through the dependency graph.

src/cargo/core/resolver/dep_cache.rs

@@ -280,10 +280,12 @@ pub fn resolve_features<'b>(
     // dep_name/feat_name` where `dep_name` does not exist. All other
     // validation is done either in `build_requirements` or
     // `build_feature_map`.
-    for dep_name in reqs.deps.keys() {
+    if parent.is_none() {
-        if !valid_dep_names.contains(dep_name) {
+        for dep_name in reqs.deps.keys() {
-            let e = RequirementError::MissingDependency(*dep_name);
+            if !valid_dep_names.contains(dep_name) {
-            return Err(e.into_activate_error(parent, s));
+                let e = RequirementError::MissingDependency(*dep_name);
+                return Err(e.into_activate_error(parent, s));
+            }
         }
     }
 

tests/testsuite/tree.rs

@@ -1937,3 +1937,113 @@ foo v1.0.0 ([ROOT]/foo)
         )
         .run();
 }
+
+#[cargo_test]
+fn dev_dep_cycle_with_feature_nested() {
+    // Checks for an issue where a cyclic dev dependency tries to activate a
+    // feature on its parent that tries to activate the feature back on the
+    // dev-dependency.
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "1.0.0"
+
+                [dev-dependencies]
+                bar = { path = "bar" }
+
+                [features]
+                a = ["bar/feat1"]
+                b = ["a"]
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "bar/Cargo.toml",
+            r#"
+                [package]
+                name = "bar"
+                version = "1.0.0"
+
+                [dependencies]
+                foo = { path = ".." }
+
+                [features]
+                feat1 = ["foo/b"]
+            "#,
+        )
+        .file("bar/src/lib.rs", "")
+        .build();
+
+    p.cargo("tree -e features")
+        .with_stdout(
+            "\
+foo v1.0.0 ([ROOT]/foo)
+[dev-dependencies]
+└── bar feature \"default\"
+    └── bar v1.0.0 ([ROOT]/foo/bar)
+        └── foo feature \"default\" (command-line)
+            └── foo v1.0.0 ([ROOT]/foo) (*)
+",
+        )
+        .run();
+
+    p.cargo("tree -e features --features a -i foo")
+        .with_stdout(
+            "\
+foo v1.0.0 ([ROOT]/foo)
+├── foo feature \"a\" (command-line)
+│   └── foo feature \"b\"
+│       └── bar feature \"feat1\"
+│           └── foo feature \"a\" (command-line) (*)
+├── foo feature \"b\" (*)
+└── foo feature \"default\" (command-line)
+    └── bar v1.0.0 ([ROOT]/foo/bar)
+        ├── bar feature \"default\"
+        │   [dev-dependencies]
+        │   └── foo v1.0.0 ([ROOT]/foo) (*)
+        └── bar feature \"feat1\" (*)
+",
+        )
+        .run();
+
+    p.cargo("tree -e features --features b -i foo")
+        .with_stdout(
+            "\
+foo v1.0.0 ([ROOT]/foo)
+├── foo feature \"a\"
+│   └── foo feature \"b\" (command-line)
+│       └── bar feature \"feat1\"
+│           └── foo feature \"a\" (*)
+├── foo feature \"b\" (command-line) (*)
+└── foo feature \"default\" (command-line)
+    └── bar v1.0.0 ([ROOT]/foo/bar)
+        ├── bar feature \"default\"
+        │   [dev-dependencies]
+        │   └── foo v1.0.0 ([ROOT]/foo) (*)
+        └── bar feature \"feat1\" (*)
+",
+        )
+        .run();
+
+    p.cargo("tree -e features --features bar/feat1 -i foo")
+        .with_stdout(
+            "\
+foo v1.0.0 ([ROOT]/foo)
+├── foo feature \"a\"
+│   └── foo feature \"b\"
+│       └── bar feature \"feat1\" (command-line)
+│           └── foo feature \"a\" (*)
+├── foo feature \"b\" (*)
+└── foo feature \"default\" (command-line)
+    └── bar v1.0.0 ([ROOT]/foo/bar)
+        ├── bar feature \"default\"
+        │   [dev-dependencies]
+        │   └── foo v1.0.0 ([ROOT]/foo) (*)
+        └── bar feature \"feat1\" (command-line) (*)
+",
+        )
+        .run();
+}