build: allow disabling snapshots for dev (#20048)

Closes #19399 (running without snapshots at all was suggested as an
alternative solution).

Adds a `__runtime_js_sources` pseudo-private feature to load extension
JS sources at runtime for faster development, instead of building and
loading snapshots or embedding sources in the binary. Will only work in
a development environment obviously.

Try running `cargo test --features __runtime_js_sources
integration::node_unit_tests::os_test`. Then break some behaviour in
`ext/node/polyfills/os.ts` e.g. make `function cpus() {}` return an
empty array, and run it again. Fix and then run again. No more build
time in between.

1 files changed, 23 insertions, 2 deletions

diff --git a/cli/ops/mod.rs b/cli/ops/mod.rs
index 5066c44b9..7af5f14af 100644
--- a/cli/ops/mod.rs
+++ b/cli/ops/mod.rs
@@ -12,17 +12,38 @@ pub mod bench;
 pub mod testing;
 
 pub fn cli_exts(npm_resolver: Arc<CliNpmResolver>) -> Vec<Extension> {
-  vec![deno_cli::init_ops(npm_resolver)]
+  vec![
+    #[cfg(not(feature = "__runtime_js_sources"))]
+    cli::init_ops(npm_resolver),
+    #[cfg(feature = "__runtime_js_sources")]
+    cli::init_ops_and_esm(npm_resolver),
+  ]
 }
 
-deno_core::extension!(deno_cli,
+// ESM parts duplicated in `../build.rs`. Keep in sync!
+deno_core::extension!(cli,
+  deps = [runtime],
   ops = [op_npm_process_state],
+  esm_entry_point = "ext:cli/99_main.js",
+  esm = [
+    dir "js",
+    "40_testing.js",
+    "99_main.js"
+  ],
   options = {
     npm_resolver: Arc<CliNpmResolver>,
   },
   state = |state, options| {
     state.put(options.npm_resolver);
   },
+  customizer = |ext: &mut deno_core::Extension| {
+    ext.esm_files.to_mut().push(deno_core::ExtensionFileSource {
+      specifier: "ext:cli/runtime/js/99_main.js",
+      code: deno_core::ExtensionFileSourceCode::LoadedFromFsDuringSnapshot(
+        deno_runtime::js::PATH_FOR_99_MAIN_JS,
+      ),
+    });
+  },
 );
 
 #[op]