feat: add --compat flag to provide built-in Node modules (#12293)

This commit adds "--compat" flag. When the flag is passed a set of mappings for
built-in Node modules is injected into the import map. If user doesn't
explicitly provide an import map (using "--import-map" flag) then a map is
created on the fly. If there are already existing mappings in import map that
would clash with built-in Node modules a set of diagnostics is printed to the
terminal with suggestions how to proceed.

1 files changed, 32 insertions, 0 deletions

diff --git a/cli/flags.rs b/cli/flags.rs
index aaff45388..dc0e932ef 100644
--- a/cli/flags.rs
+++ b/cli/flags.rs
@@ -222,6 +222,9 @@ pub struct Flags {
   pub log_level: Option<Level>,
   pub no_check: bool,
   pub no_remote: bool,
+  /// If true, a list of Node built-in modules will be injected into
+  /// the import map.
+  pub compat: bool,
   pub prompt: bool,
   pub reload: bool,
   pub repl: bool,
@@ -1490,6 +1493,7 @@ fn runtime_args<'a, 'b>(
     .arg(v8_flags_arg())
     .arg(seed_arg())
     .arg(enable_testing_features_arg())
+    .arg(compat_arg())
 }
 
 fn inspect_args<'a, 'b>(app: App<'a, 'b>) -> App<'a, 'b> {
@@ -1619,6 +1623,12 @@ fn seed_arg<'a, 'b>() -> Arg<'a, 'b> {
     })
 }
 
+fn compat_arg<'a, 'b>() -> Arg<'a, 'b> {
+  Arg::with_name("compat")
+    .long("compat")
+    .help("Node compatibility mode. Currently only enables built-in node modules like 'fs'.")
+}
+
 fn watch_arg<'a, 'b>() -> Arg<'a, 'b> {
   Arg::with_name("watch")
     .long("watch")
@@ -2228,6 +2238,7 @@ fn runtime_args_parse(
   location_arg_parse(flags, matches);
   v8_flags_arg_parse(flags, matches);
   seed_arg_parse(flags, matches);
+  compat_arg_parse(flags, matches);
   inspect_arg_parse(flags, matches);
   enable_testing_features_arg_parse(flags, matches);
 }
@@ -2313,6 +2324,12 @@ fn seed_arg_parse(flags: &mut Flags, matches: &ArgMatches) {
   }
 }
 
+fn compat_arg_parse(flags: &mut Flags, matches: &ArgMatches) {
+  if matches.is_present("compat") {
+    flags.compat = true;
+  }
+}
+
 fn no_check_arg_parse(flags: &mut Flags, matches: &clap::ArgMatches) {
   if matches.is_present("no-check") {
     flags.no_check = true;
@@ -4431,4 +4448,19 @@ mod tests {
       .to_string()
       .contains("Expected protocol \"http\" or \"https\""));
   }
+
+  #[test]
+  fn compat() {
+    let r = flags_from_vec(svec!["deno", "run", "--compat", "foo.js"]);
+    assert_eq!(
+      r.unwrap(),
+      Flags {
+        subcommand: DenoSubcommand::Run(RunFlags {
+          script: "foo.js".to_string(),
+        }),
+        compat: true,
+        ..Flags::default()
+      }
+    );
+  }
 }