Avoid fingerprint invalidation when reordering the declared features

src/cargo/core/compiler/fingerprint/mod.rs

@@ -1443,7 +1443,9 @@ fn calculate_normal(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Finger
         allow_features.hash(&mut config);
     }
     let compile_kind = unit.kind.fingerprint_hash();
-    let declared_features = unit.pkg.summary().features().keys().collect::<Vec<_>>();
+    let mut declared_features = unit.pkg.summary().features().keys().collect::<Vec<_>>();
+    declared_features.sort(); // to avoid useless rebuild if the user orders it's features
+                              // differently
     Ok(Fingerprint {
         rustc: util::hash_u64(&cx.bcx.rustc().verbose_version),
         target: util::hash_u64(&unit.target),

tests/testsuite/check_cfg.rs

@@ -165,6 +165,25 @@ fn features_fingerprint() {
         .with_stderr_does_not_contain("[..]unexpected_cfgs[..]")
         .run();
 
+    p.cargo("check -v -Zcheck-cfg")
+        .masquerade_as_nightly_cargo(&["check-cfg"])
+        .with_stderr_does_not_contain("[..]rustc[..]")
+        .run();
+
+    // checking that re-ordering the features does not invalid the fingerprint
+    p.change_file(
+        "Cargo.toml",
+        r#"
+            [package]
+            name = "foo"
+            version = "0.1.0"
+
+            [features]
+            f_b = []
+            f_a = []
+        "#,
+    );
+
     p.cargo("check -v -Zcheck-cfg")
         .masquerade_as_nightly_cargo(&["check-cfg"])
         .with_stderr_does_not_contain("[..]rustc[..]")