feat(unstable): ability to `npm install` then `deno run main.ts` (#20967)

This PR adds a new unstable "bring your own node_modules" (BYONM)
functionality currently behind a `--unstable-byonm` flag (`"unstable":
["byonm"]` in a deno.json).

This enables users to run a separate install command (ex. `npm install`,
`pnpm install`) then run `deno run main.ts` and Deno will respect the
layout of the node_modules directory as setup by the separate install
command. It also works with npm/yarn/pnpm workspaces.

For this PR, the behaviour is opted into by specifying
`--unstable-byonm`/`"unstable": ["byonm"]`, but in the future we may
make this the default behaviour as outlined in
https://github.com/denoland/deno/issues/18967#issuecomment-1761248941

This is an extremely rough initial implementation. Errors are
terrible in this and the LSP requires frequent restarts. Improvements
will be done in follow up PRs.

1 files changed, 10 insertions, 5 deletions

diff --git a/test_util/src/builders.rs b/test_util/src/builders.rs
index 17871baa1..39771e088 100644
--- a/test_util/src/builders.rs
+++ b/test_util/src/builders.rs
@@ -227,7 +227,7 @@ pub struct TestCommandBuilder {
 }
 
 impl TestCommandBuilder {
-  pub fn command_name(mut self, name: impl AsRef<OsStr>) -> Self {
+  pub fn name(mut self, name: impl AsRef<OsStr>) -> Self {
     self.command_name = name.as_ref().to_string_lossy().to_string();
     self
   }
@@ -306,7 +306,11 @@ impl TestCommandBuilder {
   }
 
   fn build_command_path(&self) -> PathRef {
-    let command_name = &self.command_name;
+    let command_name = if cfg!(windows) && self.command_name == "npm" {
+      "npm.cmd"
+    } else {
+      &self.command_name
+    };
     if command_name == "deno" {
       deno_exe_path()
     } else {
@@ -407,11 +411,11 @@ impl TestCommandBuilder {
       command.env_clear();
     }
     command.env("DENO_DIR", self.context.deno_dir.path());
-    let envs = self.build_envs();
+    let mut envs = self.build_envs();
     if !envs.contains_key("NPM_CONFIG_REGISTRY") {
-      command.env("NPM_CONFIG_REGISTRY", npm_registry_unset_url());
+      envs.insert("NPM_CONFIG_REGISTRY".to_string(), npm_registry_unset_url());
     }
-    command.envs(self.build_envs());
+    command.envs(envs);
     command.current_dir(cwd);
     command.stdin(Stdio::piped());
 
@@ -527,6 +531,7 @@ impl Drop for TestCommandOutput {
 
     // now ensure the exit code was asserted
     if !*self.asserted_exit_code.borrow() && self.exit_code != Some(0) {
+      self.print_output();
       panic!(
         "The non-zero exit code of the command was not asserted: {:?}",
         self.exit_code,