feat: support .mjs extension resolution (denoland#2283)

Removed `extmap` and added .mjs entry in `map_file_extension`.
The assert in the compiler does not need to be updated, since it is
resolving from the compiled cache instead of elsewhere (notice the .map
is asserted next to it)

cli/deno_dir.rs

@@ -26,16 +26,6 @@ use std::str;
 use url;
 use url::Url;
 
-/// Gets corresponding MediaType given extension
-fn extmap(ext: &str) -> msg::MediaType {
-  match ext {
-    "ts" => msg::MediaType::TypeScript,
-    "js" => msg::MediaType::JavaScript,
-    "json" => msg::MediaType::Json,
-    _ => msg::MediaType::Unknown,
-  }
-}
-
 #[derive(Clone)]
 pub struct DenoDir {
   // Example: /Users/rld/.deno/
@@ -553,6 +543,7 @@ fn map_file_extension(path: &Path) -> msg::MediaType {
     Some(os_str) => match os_str.to_str() {
       Some("ts") => msg::MediaType::TypeScript,
       Some("js") => msg::MediaType::JavaScript,
+      Some("mjs") => msg::MediaType::JavaScript,
       Some("json") => msg::MediaType::Json,
       _ => msg::MediaType::Unknown,
     },
@@ -871,11 +862,7 @@ fn save_source_code_headers(
     let mime_type_string = mime_type.clone().unwrap();
     let resolved_mime_type =
       { map_content_type(Path::new(""), Some(mime_type_string.as_str())) };
-    let ext = p
-      .extension()
-      .map(|x| x.to_str().unwrap_or(""))
-      .unwrap_or("");
-    let ext_based_mime_type = extmap(&ext);
+    let ext_based_mime_type = map_file_extension(&p);
     // Add mime to headers only when content type is different from extension.
     if ext_based_mime_type == msg::MediaType::Unknown
       || resolved_mime_type != ext_based_mime_type

tests/021_mjs_modules.test

@@ -0,0 +1,2 @@
+args: --reload tests/021_mjs_modules.ts
+output: tests/021_mjs_modules.ts.out

tests/021_mjs_modules.ts

@@ -0,0 +1,2 @@
+import { isMod5 } from "./subdir/mod5.mjs";
+console.log(isMod5);

tests/021_mjs_modules.ts.out

@@ -0,0 +1 @@
+true

tests/subdir/mod5.mjs

@@ -0,0 +1 @@
+export const isMod5 = true;