js/esbuild: Don't try to resolve packages in /assets marked as external

Fixes gohugoio#13183

internal/js/esbuild/resolve.go

@@ -167,6 +167,17 @@ func createBuildPlugins(rs *resources.Spec, assetsResolver *fsResolver, depsMana
 			}
 		}
 
+		for _, ext := range opts.Externals {
+			// ESBuild will do a more thorough check for packages resolved in node_modules,
+			// but we need to make sure that we don't try to resolve these in the /assets folder.
+			if ext == impPath {
+				return api.OnResolveResult{
+					Path:     impPath,
+					External: true,
+				}, nil
+			}
+		}
+
 		if opts.ImportOnResolveFunc != nil {
 			if s := opts.ImportOnResolveFunc(impPath, args); s != "" {
 				return api.OnResolveResult{Path: s, Namespace: NsHugoImportResolveFunc}, nil

resources/resource_transformers/js/js_integration_test.go

@@ -391,3 +391,32 @@ class A {}
 		}).Build()
 	b.AssertFileContent("public/js/main.js", "__decorateClass")
 }
+
+// Issue 13183.
+func TestExternalsInAssets(t *testing.T) {
+	files := `
+-- assets/js/util1.js --
+export function hello1() {
+	return 'abcd';
+}
+-- assets/js/util2.js --
+export function hello2() {
+	return 'efgh';
+}
+-- assets/js/main.js --
+import { hello1 } from './util1.js';
+import { hello2 } from './util2.js';
+
+hello1();
+hello2();
+-- layouts/index.html --
+Home.
+{{ $js := resources.Get "js/main.js" | js.Build (dict "externals" (slice "./util1.js")) }}
+{{ $js.Publish }}
+`
+
+	b := hugolib.Test(t, files, hugolib.TestOptOsFs())
+
+	b.AssertFileContent("public/js/main.js", "efgh")
+	b.AssertFileContent("public/js/main.js", "! abcd")
+}