Add regression test

Author: JonathanBrouwer

tests/ui/macros/cfg_select.rs

@@ -95,3 +95,17 @@ cfg_select! {
     cfg!() => {}
     //~^ ERROR expected one of `(`, `::`, `=>`, or `=`, found `!`
 }
+
+cfg_select! {
+    true => {}
+    invalid_cfg1 => {}
+    //~^ WARN unexpected `cfg` condition name
+    _ => {}
+}
+
+cfg_select! {
+    invalid_cfg2 => {}
+    //~^ WARN unexpected `cfg` condition name
+    true => {}
+    _ => {}
+}

tests/ui/macros/cfg_select.stderr

@@ -65,7 +65,27 @@ error: expected one of `(`, `::`, `=>`, or `=`, found `!`
 LL |     cfg!() => {}
    |        ^ expected one of `(`, `::`, `=>`, or `=`
 
-error: aborting due to 9 previous errors; 1 warning emitted
+warning: unexpected `cfg` condition name: `invalid_cfg1`
+  --> $DIR/cfg_select.rs:101:5
+   |
+LL |     invalid_cfg1 => {}
+   |     ^^^^^^^^^^^^
+   |
+   = help: expected names are: `FALSE` and `test` and 31 more
+   = help: to expect this configuration use `--check-cfg=cfg(invalid_cfg1)`
+   = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
+   = note: `#[warn(unexpected_cfgs)]` on by default
+
+warning: unexpected `cfg` condition name: `invalid_cfg2`
+  --> $DIR/cfg_select.rs:107:5
+   |
+LL |     invalid_cfg2 => {}
+   |     ^^^^^^^^^^^^
+   |
+   = help: to expect this configuration use `--check-cfg=cfg(invalid_cfg2)`
+   = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
+
+error: aborting due to 9 previous errors; 3 warnings emitted
 
 Some errors have detailed explanations: E0537, E0539.
 For more information about an error, try `rustc --explain E0537`.