1 files changed, 29 insertions, 9 deletions
diff --git a/core/extensions.rs b/core/extensions.rs
index 94c4a2a79..9b4fb203a 100644
--- a/core/extensions.rs
+++ b/core/extensions.rs
@@ -23,23 +23,43 @@ pub enum ExtensionFileSourceCode {
   LoadedFromFsDuringSnapshot(PathBuf),
 }
 
-impl ExtensionFileSourceCode {
+#[derive(Clone, Debug)]
+pub struct ExtensionFileSource {
+  pub specifier: &'static str,
+  pub code: ExtensionFileSourceCode,
+}
+
+impl ExtensionFileSource {
+  fn find_non_ascii(s: &str) -> String {
+    s.chars().filter(|c| !c.is_ascii()).collect::<String>()
+  }
+
   pub fn load(&self) -> Result<ModuleCode, Error> {
-    match self {
-      ExtensionFileSourceCode::IncludedInBinary(code) => Ok((*code).into()),
+    match &self.code {
+      ExtensionFileSourceCode::IncludedInBinary(code) => {
+        debug_assert!(
+          code.is_ascii(),
+          "Extension code must be 7-bit ASCII: {} (found {})",
+          self.specifier,
+          Self::find_non_ascii(code)
+        );
+        Ok((*code).into())
+      }
       ExtensionFileSourceCode::LoadedFromFsDuringSnapshot(path) => {
         let msg = || format!("Failed to read \"{}\"", path.display());
-        Ok(std::fs::read_to_string(path).with_context(msg)?.into())
+        let s = std::fs::read_to_string(path).with_context(msg)?;
+        debug_assert!(
+          s.is_ascii(),
+          "Extension code must be 7-bit ASCII: {} (found {})",
+          self.specifier,
+          Self::find_non_ascii(&s)
+        );
+        Ok(s.into())
       }
     }
   }
 }
 
-#[derive(Clone, Debug)]
-pub struct ExtensionFileSource {
-  pub specifier: &'static str,
-  pub code: ExtensionFileSourceCode,
-}
 pub type OpFnRef = v8::FunctionCallback;
 pub type OpMiddlewareFn = dyn Fn(OpDecl) -> OpDecl;
 pub type OpStateFn = dyn FnOnce(&mut OpState);