perf: avoid building module graph if dynamic specifier already in graph (#24035)

cli/module_loader.rs

@@ -171,7 +171,7 @@ impl ModuleLoadPreparer {
       )
       .await?;
 
-    self.module_graph_builder.graph_roots_valid(graph, roots)?;
+    self.graph_roots_valid(graph, roots)?;
 
     // write the lockfile if there is one
     if let Some(lockfile) = &self.lockfile {
@@ -205,6 +205,14 @@ impl ModuleLoadPreparer {
 
     Ok(())
   }
+
+  pub fn graph_roots_valid(
+    &self,
+    graph: &ModuleGraph,
+    roots: &[ModuleSpecifier],
+  ) -> Result<(), AnyError> {
+    self.module_graph_builder.graph_roots_valid(graph, roots)
+  }
 }
 
 struct SharedCliModuleLoaderState {
@@ -806,8 +814,26 @@ impl<TGraphContainer: ModuleGraphContainer> ModuleLoader
     let inner = self.0.clone();
 
     async move {
-      let graph_container = inner.graph_container.clone();
-      let module_load_preparer = inner.shared.module_load_preparer.clone();
+      let graph_container = &inner.graph_container;
+      let module_load_preparer = &inner.shared.module_load_preparer;
+
+      if is_dynamic {
+        // When the specifier is already in the graph then it means it
+        // was previously loaded, so we can skip that and only check if
+        // this part of the graph is valid.
+        //
+        // This doesn't acquire a graph update permit because that will
+        // clone the graph which is a bit slow.
+        let graph = graph_container.graph();
+        if !graph.roots.is_empty() && graph.get(&specifier).is_some() {
+          log::debug!("Skipping prepare module load.");
+          // roots are already validated so we can skip those
+          if !graph.roots.contains(&specifier) {
+            module_load_preparer.graph_roots_valid(&graph, &[specifier])?;
+          }
+          return Ok(());
+        }
+      }
 
       let root_permissions = if is_dynamic {
         inner.dynamic_permissions.clone()

tests/specs/run/dynamic_already_prepared/__test__.jsonc

@@ -0,0 +1,8 @@
+{
+  "tests": {
+    "skips_prepare_module_load": {
+      "args": "run -A --log-level=debug main.ts",
+      "output": "main.out"
+    }
+  }
+}

tests/specs/run/dynamic_already_prepared/dynamic.ts

@@ -0,0 +1 @@
+console.log(1);

tests/specs/run/dynamic_already_prepared/dynamic2.ts

@@ -0,0 +1 @@
+await import("./dynamic3.ts");

tests/specs/run/dynamic_already_prepared/dynamic3.ts

@@ -0,0 +1 @@
+await import("./dynamic.ts");

tests/specs/run/dynamic_already_prepared/main.out

@@ -0,0 +1 @@
+[WILDCARD]Prepared module load.[WILDCARD]Skipping prepare module load.[WILDCARD]Skipping prepare module load.[WILDCARD]Skipping prepare module load.[WILDCARD]

tests/specs/run/dynamic_already_prepared/main.ts

@@ -0,0 +1,2 @@
+await import("./dynamic.ts");
+await import("./dynamic2.ts");