fix(install): don't re-set up node_modules if running lifecycle script (#26984)

Fixes https://github.com/denoland/deno/issues/26904

If using `nodeModulesDir: "auto"`, it's possible for the lifecycle
script subprocess to try to set up the node_modules dir (despite the
fact that we're already doing that). If it does that, it hangs trying to
acquire the file lock on the node_modules dir.

As a fix, don't try to set up node_modules if we're running as part of a
lifecycle script.

Ideally we'd have better control over when we do and don't set up
node_modules automatically (that's the underlying problem behind #25782
as well)

cli/npm/managed/resolvers/common/lifecycle_scripts.rs

@@ -182,6 +182,12 @@ impl<'a> LifecycleScripts<'a> {
       );
 
       let mut env_vars = crate::task_runner::real_env_vars();
+      // so the subprocess can detect that it is running as part of a lifecycle script,
+      // and avoid trying to set up node_modules again
+      env_vars.insert(
+        LIFECYCLE_SCRIPTS_RUNNING_ENV_VAR.to_string(),
+        "1".to_string(),
+      );
       // we want to pass the current state of npm resolution down to the deno subprocess
       // (that may be running as part of the script). we do this with an inherited temp file
       //
@@ -303,6 +309,13 @@ impl<'a> LifecycleScripts<'a> {
   }
 }
 
+const LIFECYCLE_SCRIPTS_RUNNING_ENV_VAR: &str =
+  "DENO_INTERNAL_IS_LIFECYCLE_SCRIPT";
+
+pub fn is_running_lifecycle_script() -> bool {
+  std::env::var(LIFECYCLE_SCRIPTS_RUNNING_ENV_VAR).is_ok()
+}
+
 // take in all (non copy) packages from snapshot,
 // and resolve the set of available binaries to create
 // custom commands available to the task runner

cli/npm/managed/resolvers/local.rs

@@ -298,6 +298,12 @@ async fn sync_resolution_with_fs(
     return Ok(()); // don't create the directory
   }
 
+  // don't set up node_modules (and more importantly try to acquire the file lock)
+  // if we're running as part of a lifecycle script
+  if super::common::lifecycle_scripts::is_running_lifecycle_script() {
+    return Ok(());
+  }
+
   let deno_local_registry_dir = root_node_modules_dir_path.join(".deno");
   let deno_node_modules_dir = deno_local_registry_dir.join("node_modules");
   fs::create_dir_all(&deno_node_modules_dir).with_context(|| {