test: add ui test for highlighter

Author: JayanAXHF

compiler/rustc_driver_impl/src/lib.rs

@@ -86,7 +86,7 @@ pub mod args;
 pub mod pretty;
 #[macro_use]
 mod print;
-mod highlighter;
+pub mod highlighter;
 mod session_diagnostics;
 
 // Keep the OS parts of this `cfg` in sync with the `cfg` on the `libc`

tests/ui-fulldeps/explain_highlighter.rs

@@ -0,0 +1,29 @@
+//@ run-pass
+//@ check-run-results
+
+#![feature(rustc_private)]
+use std::io::Write;
+extern crate rustc_driver;
+extern crate rustc_driver_impl;
+
+use rustc_driver_impl::highlighter::highlight;
+
+const TEST_INPUT: &str = "
+struct Foo;
+
+fn baz(x: i32) {
+    // A function
+}
+
+fn main() {
+    let foo = Foo;
+    foo.bar();
+}
+";
+
+fn main() {
+    let mut buf = Vec::new();
+    highlight(TEST_INPUT, &mut buf).unwrap();
+    let mut stdout = std::io::stdout();
+    stdout.write_all(&buf).unwrap();
+}

tests/ui-fulldeps/explain_highlighter.run.stdout

@@ -0,0 +1,12 @@
+
+struct Foo;
+
+fn baz(x: i32) {
+    // A function
+}
+
+fn main() {
+    let foo = Foo;
+    foo.bar();
+}
+