4 files changed, 93 insertions, 6 deletions

diff --git a/cli/npm/resolvers/common.rs b/cli/npm/resolvers/common.rs
index 508b783c9..7769d2322 100644
--- a/cli/npm/resolvers/common.rs
+++ b/cli/npm/resolvers/common.rs
@@ -10,6 +10,7 @@ use deno_core::futures;
 use deno_core::futures::future::BoxFuture;
 use deno_core::url::Url;
 
+use crate::npm::resolution::NpmResolutionSnapshot;
 use crate::npm::NpmCache;
 use crate::npm::NpmPackageReq;
 use crate::npm::NpmResolutionPackage;
@@ -39,6 +40,8 @@ pub trait InnerNpmPackageResolver: Send + Sync {
   ) -> BoxFuture<'static, Result<(), AnyError>>;
 
   fn ensure_read_permission(&self, path: &Path) -> Result<(), AnyError>;
+
+  fn snapshot(&self) -> NpmResolutionSnapshot;
 }
 
 /// Caches all the packages in parallel.
diff --git a/cli/npm/resolvers/global.rs b/cli/npm/resolvers/global.rs
index 94b963898..c1b6818fd 100644
--- a/cli/npm/resolvers/global.rs
+++ b/cli/npm/resolvers/global.rs
@@ -13,6 +13,7 @@ use deno_core::futures::FutureExt;
 use deno_core::url::Url;
 
 use crate::npm::resolution::NpmResolution;
+use crate::npm::resolution::NpmResolutionSnapshot;
 use crate::npm::resolvers::common::cache_packages;
 use crate::npm::NpmCache;
 use crate::npm::NpmPackageId;
@@ -31,9 +32,13 @@ pub struct GlobalNpmPackageResolver {
 }
 
 impl GlobalNpmPackageResolver {
-  pub fn new(cache: NpmCache, api: NpmRegistryApi) -> Self {
+  pub fn new(
+    cache: NpmCache,
+    api: NpmRegistryApi,
+    initial_snapshot: Option<NpmResolutionSnapshot>,
+  ) -> Self {
     let registry_url = api.base_url().to_owned();
-    let resolution = Arc::new(NpmResolution::new(api));
+    let resolution = Arc::new(NpmResolution::new(api, initial_snapshot));
 
     Self {
       cache,
@@ -105,4 +110,8 @@ impl InnerNpmPackageResolver for GlobalNpmPackageResolver {
     let registry_path = self.cache.registry_folder(&self.registry_url);
     ensure_registry_read_permission(&registry_path, path)
   }
+
+  fn snapshot(&self) -> NpmResolutionSnapshot {
+    self.resolution.snapshot()
+  }
 }
diff --git a/cli/npm/resolvers/local.rs b/cli/npm/resolvers/local.rs
index fa2ad4275..10ac8abfa 100644
--- a/cli/npm/resolvers/local.rs
+++ b/cli/npm/resolvers/local.rs
@@ -47,9 +47,10 @@ impl LocalNpmPackageResolver {
     cache: NpmCache,
     api: NpmRegistryApi,
     node_modules_folder: PathBuf,
+    initial_snapshot: Option<NpmResolutionSnapshot>,
   ) -> Self {
     let registry_url = api.base_url().to_owned();
-    let resolution = Arc::new(NpmResolution::new(api));
+    let resolution = Arc::new(NpmResolution::new(api, initial_snapshot));
 
     Self {
       cache,
@@ -180,6 +181,10 @@ impl InnerNpmPackageResolver for LocalNpmPackageResolver {
   fn ensure_read_permission(&self, path: &Path) -> Result<(), AnyError> {
     ensure_registry_read_permission(&self.root_node_modules_path, path)
   }
+
+  fn snapshot(&self) -> NpmResolutionSnapshot {
+    self.resolution.snapshot()
+  }
 }
 
 /// Creates a pnpm style folder structure.
diff --git a/cli/npm/resolvers/mod.rs b/cli/npm/resolvers/mod.rs
index 3a40340f0..4b4ec4723 100644
--- a/cli/npm/resolvers/mod.rs
+++ b/cli/npm/resolvers/mod.rs
@@ -8,9 +8,13 @@ use deno_ast::ModuleSpecifier;
 use deno_core::anyhow::bail;
 use deno_core::error::custom_error;
 use deno_core::error::AnyError;
+use deno_core::serde_json;
 use deno_runtime::deno_node::PathClean;
 use deno_runtime::deno_node::RequireNpmResolver;
 use global::GlobalNpmPackageResolver;
+use once_cell::sync::Lazy;
+use serde::Deserialize;
+use serde::Serialize;
 
 use std::path::Path;
 use std::path::PathBuf;
@@ -20,15 +24,50 @@ use crate::fs_util;
 
 use self::common::InnerNpmPackageResolver;
 use self::local::LocalNpmPackageResolver;
+use super::resolution::NpmResolutionSnapshot;
 use super::NpmCache;
 use super::NpmPackageReq;
 use super::NpmRegistryApi;
 
+const RESOLUTION_STATE_ENV_VAR_NAME: &str =
+  "DENO_DONT_USE_INTERNAL_NODE_COMPAT_STATE";
+
+static IS_NPM_MAIN: Lazy<bool> =
+  Lazy::new(|| std::env::var(RESOLUTION_STATE_ENV_VAR_NAME).is_ok());
+
+/// State provided to the process via an environment variable.
+#[derive(Debug, Serialize, Deserialize)]
+struct NpmProcessState {
+  snapshot: NpmResolutionSnapshot,
+  local_node_modules_path: Option<String>,
+}
+
+impl NpmProcessState {
+  pub fn was_set() -> bool {
+    *IS_NPM_MAIN
+  }
+
+  pub fn take() -> Option<NpmProcessState> {
+    // initialize the lazy before we remove the env var below
+    if !Self::was_set() {
+      return None;
+    }
+
+    let state = std::env::var(RESOLUTION_STATE_ENV_VAR_NAME).ok()?;
+    let state = serde_json::from_str(&state).ok()?;
+    // remove the environment variable so that sub processes
+    // that are spawned do not also use this.
+    std::env::remove_var(RESOLUTION_STATE_ENV_VAR_NAME);
+    Some(state)
+  }
+}
+
 #[derive(Clone)]
 pub struct NpmPackageResolver {
   unstable: bool,
   no_npm: bool,
   inner: Arc<dyn InnerNpmPackageResolver>,
+  local_node_modules_path: Option<PathBuf>,
 }
 
 impl NpmPackageResolver {
@@ -39,19 +78,30 @@ impl NpmPackageResolver {
     no_npm: bool,
     local_node_modules_path: Option<PathBuf>,
   ) -> Self {
-    let inner: Arc<dyn InnerNpmPackageResolver> = match local_node_modules_path
+    let process_npm_state = NpmProcessState::take();
+    let local_node_modules_path = local_node_modules_path.or_else(|| {
+      process_npm_state
+        .as_ref()
+        .and_then(|s| s.local_node_modules_path.as_ref().map(PathBuf::from))
+    });
+    let maybe_snapshot = process_npm_state.map(|s| s.snapshot);
+    let inner: Arc<dyn InnerNpmPackageResolver> = match &local_node_modules_path
     {
       Some(node_modules_folder) => Arc::new(LocalNpmPackageResolver::new(
         cache,
         api,
-        node_modules_folder,
+        node_modules_folder.clone(),
+        maybe_snapshot,
       )),
-      None => Arc::new(GlobalNpmPackageResolver::new(cache, api)),
+      None => {
+        Arc::new(GlobalNpmPackageResolver::new(cache, api, maybe_snapshot))
+      }
     };
     Self {
       unstable,
       no_npm,
       inner,
+      local_node_modules_path,
     }
   }
 
@@ -137,6 +187,26 @@ impl NpmPackageResolver {
 
     self.inner.add_package_reqs(packages).await
   }
+
+  // If the main module should be treated as being in an npm package.
+  // This is triggered via a secret environment variable which is used
+  // for functionality like child_process.fork. Users should NOT depend
+  // on this functionality.
+  pub fn is_npm_main(&self) -> bool {
+    NpmProcessState::was_set()
+  }
+
+  /// Gets the state of npm for the process.
+  pub fn get_npm_process_state(&self) -> String {
+    serde_json::to_string(&NpmProcessState {
+      snapshot: self.inner.snapshot(),
+      local_node_modules_path: self
+        .local_node_modules_path
+        .as_ref()
+        .map(|p| p.to_string_lossy().to_string()),
+    })
+    .unwrap()
+  }
 }
 
 impl RequireNpmResolver for NpmPackageResolver {