4 files changed, 34 insertions, 0 deletions
diff --git a/cli/http_util.rs b/cli/http_util.rs
index 12e70e3e7..2278afc8d 100644
--- a/cli/http_util.rs
+++ b/cli/http_util.rs
@@ -117,6 +117,15 @@ pub fn fetch_once(
 
     let mut headers_: HashMap<String, String> = HashMap::new();
     let headers = response.headers();
+
+    if let Some(warning) = headers.get("X-Deno-Warning") {
+      eprintln!(
+        "{} {}",
+        crate::colors::yellow("Warning".to_string()),
+        warning.to_str().unwrap()
+      );
+    }
+
     for key in headers.keys() {
       let key_str = key.to_string();
       let values = headers.get_all(key);
diff --git a/cli/tests/integration_tests.rs b/cli/tests/integration_tests.rs
index 7ad7781de..4897422b9 100644
--- a/cli/tests/integration_tests.rs
+++ b/cli/tests/integration_tests.rs
@@ -13,6 +13,28 @@ use std::process::Command;
 use tempfile::TempDir;
 
 #[test]
+fn x_deno_warning() {
+  let g = util::http_server();
+  let output = util::deno_cmd()
+    .current_dir(util::root_path())
+    .arg("run")
+    .arg("--reload")
+    .arg("http://127.0.0.1:4545/cli/tests/x_deno_warning.js")
+    .stdout(std::process::Stdio::piped())
+    .stderr(std::process::Stdio::piped())
+    .spawn()
+    .unwrap()
+    .wait_with_output()
+    .unwrap();
+  assert!(output.status.success());
+  let stdout_str = std::str::from_utf8(&output.stdout).unwrap().trim();
+  let stderr_str = std::str::from_utf8(&output.stderr).unwrap().trim();
+  assert_eq!("testing x-deno-warning header", stdout_str);
+  assert!(deno::colors::strip_ansi_codes(stderr_str).contains("Warning foobar"));
+  drop(g);
+}
+
+#[test]
 fn no_color() {
   let output = util::deno_cmd()
     .current_dir(util::root_path())
diff --git a/cli/tests/x_deno_warning.js b/cli/tests/x_deno_warning.js
new file mode 100644
index 000000000..34b950566
--- /dev/null
+++ b/cli/tests/x_deno_warning.js
@@ -0,0 +1 @@
+console.log("testing x-deno-warning header");
diff --git a/cli/tests/x_deno_warning.js.header b/cli/tests/x_deno_warning.js.header
new file mode 100644
index 000000000..9a8ba0190
--- /dev/null
+++ b/cli/tests/x_deno_warning.js.header
@@ -0,0 +1,2 @@
+Content-Type: application/javascript
+X-Deno-Warning: foobar
+\ No newline at end of file