Improve diagnostic for unexpected feature config name from Cargo

2 files changed, 25 insertions, 0 deletions

diff --git a/tests/ui/check-cfg/cargo-feature.rs b/tests/ui/check-cfg/cargo-feature.rs
new file mode 100644
index 00000000000..ea48c6ea201
--- /dev/null
+++ b/tests/ui/check-cfg/cargo-feature.rs
@@ -0,0 +1,14 @@
+// This test checks that when no features are passed by Cargo we
+// suggest adding some in the Cargo.toml instead of vomitting a
+// list of all the expected names
+//
+// check-pass
+// rustc-env:CARGO=/usr/bin/cargo
+// compile-flags: --check-cfg=cfg() -Z unstable-options
+// error-pattern:Cargo.toml
+
+#[cfg(feature = "serde")]
+//~^ WARNING unexpected `cfg` condition name
+fn ser() {}
+
+fn main() {}
diff --git a/tests/ui/check-cfg/cargo-feature.stderr b/tests/ui/check-cfg/cargo-feature.stderr
new file mode 100644
index 00000000000..619410a28f3
--- /dev/null
+++ b/tests/ui/check-cfg/cargo-feature.stderr
@@ -0,0 +1,11 @@
+warning: unexpected `cfg` condition name: `feature`
+  --> $DIR/cargo-feature.rs:10:7
+   |
+LL | #[cfg(feature = "serde")]
+   |       ^^^^^^^^^^^^^^^^^
+   |
+   = help: consider defining some features in `Cargo.toml`
+   = note: `#[warn(unexpected_cfgs)]` on by default
+
+warning: 1 warning emitted
+