Perform build-time alerts in test suite using build-alert crate

Author: dtolnay

tests/features/Cargo.toml

@@ -9,7 +9,7 @@ publish = false
 path = "lib.rs"
 
 [dependencies]
-syn-test-suite-feature-check = { path = "macro" }
+build-alert = "0.1"
 
 [features]
-all-features = ["syn-test-suite-feature-check/all-features"]
+all-features = []

tests/features/lib.rs

@@ -1 +1,16 @@
-syn_test_suite_feature_check::check!();
+#[cfg(debug_assertions)]
+build_alert::yellow! {"
+NOTE:  use --release
+  Syn's test suite has some tests that run on every source file
+  and test case in the rust-lang/rust repo, which can be pretty
+  slow in debug mode. Consider running cargo test with `--release`
+  to speed things up.
+"}
+
+#[cfg(not(feature = "all-features"))]
+build_alert::red! {"
+ERROR:  use --all-features
+  Syn's test suite normally only works with all-features enabled.
+  Run again with `--all-features`, or run with `--features test`
+  to bypass this check.
+"}