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, 28 insertions, 1 deletions

diff --git a/cli/proc_state.rs b/cli/proc_state.rs
index 2c61ba51f..48dc335f0 100644
--- a/cli/proc_state.rs
+++ b/cli/proc_state.rs
@@ -36,6 +36,7 @@ use deno_tls::rustls_native_certs::load_native_certs;
 use deno_tls::webpki_roots::TLS_SERVER_ROOTS;
 use import_map::ImportMap;
 use log::debug;
+use log::info;
 use log::warn;
 use std::collections::HashMap;
 use std::collections::HashSet;
@@ -182,7 +183,7 @@ impl ProcState {
         None
       };
 
-    let maybe_import_map: Option<ImportMap> =
+    let mut maybe_import_map: Option<ImportMap> =
       match flags.import_map_path.as_ref() {
         None => None,
         Some(import_map_url) => {
@@ -204,6 +205,32 @@ impl ProcState {
         }
       };
 
+    if flags.compat {
+      let mut import_map = match maybe_import_map {
+        Some(import_map) => import_map,
+        None => {
+          // INFO: we're creating an empty import map, with its specifier pointing
+          // to `CWD/node_import_map.json` to make sure the map still works as expected.
+          let import_map_specifier =
+            std::env::current_dir()?.join("node_import_map.json");
+          ImportMap::from_json(import_map_specifier.to_str().unwrap(), "{}")
+            .unwrap()
+        }
+      };
+      let node_builtins = crate::compat::get_mapped_node_builtins();
+      let diagnostics = import_map.update_imports(node_builtins)?;
+
+      if !diagnostics.is_empty() {
+        info!("Some Node built-ins were not added to the import map:");
+        for diagnostic in diagnostics {
+          info!("  - {}", diagnostic);
+        }
+        info!("If you want to use Node built-ins provided by Deno remove listed specifiers from \"imports\" mapping in the import map file.");
+      }
+
+      maybe_import_map = Some(import_map);
+    }
+
     let maybe_inspect_host = flags.inspect.or(flags.inspect_brk);
     let maybe_inspector_server = maybe_inspect_host.map(|host| {
       Arc::new(InspectorServer::new(host, version::get_user_agent()))