executor: move current-thread into crate (#1447)

The `CurrentThread` executor is exposed using a feature flag.

Refs: #1264

ui-tests/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "ui-tests"
+version = "0.1.0"
+authors = ["Carl Lerche <[email protected]>"]
+edition = "2018"
+publish = false
+
+[features]
+executor-without-current-thread = ["tokio-executor"]
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+tokio-executor = { path = "../tokio-executor", optional = true }
+
+[dev-dependencies]
+trybuild = "1.0"

ui-tests/README.md

@@ -0,0 +1,2 @@
+Tests the various combination of feature flags. This is broken out to a separate
+crate to work around limitations with cargo features.

ui-tests/src/lib.rs

@@ -0,0 +1,2 @@
+#[cfg(feature = "tokio-executor")]
+pub use tokio_executor;

ui-tests/tests/features.rs

@@ -0,0 +1,9 @@
+#[test]
+fn features() {
+    let t = trybuild::TestCases::new();
+
+    #[cfg(feature = "executor-without-current-thread")]
+    t.compile_fail("tests/ui/executor_without_current_thread.rs");
+
+    drop(t);
+}

ui-tests/tests/ui/executor_without_current_thread.rs

@@ -0,0 +1,3 @@
+use ui_tests::tokio_executor::current_thread;
+
+fn main() {}

ui-tests/tests/ui/executor_without_current_thread.stderr

@@ -0,0 +1,7 @@
+error[E0432]: unresolved import `ui_tests::tokio_executor::current_thread`
+ --> $DIR/executor_without_current_thread.rs:1:5
+  |
+1 | use ui_tests::tokio_executor::current_thread;
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no `current_thread` in `tokio_executor`
+
+For more information about this error, try `rustc --explain E0432`.