add support for dynamic import()

must be hidden from closure to prevent it trying to rewrite

src/dev/demo/esm/a.cljs

@@ -1,5 +1,6 @@
 (ns demo.esm.a
-  (:require ["https://cdn.pika.dev/preact@^10.0.0" :as x]))
+  (:require
+    ["https://cdn.pika.dev/preact@^10.0.0" :as x]))
 
 (def foo "demo.esm.a/foo")
 

src/main/shadow/build/targets/esm.clj

@@ -145,6 +145,12 @@
                          :entries entries
                          :default default?)
                   (cond->
+                    ;; closure will try to rewrite dynamic import() calls
+                    ;; but its just a regular function so we alias and extern it
+                    ;; so closure doesn't rename it.
+                    default?
+                    (update :module-externs conj "shadow_esm_import")
+
                     ;; REPL client - only for watch (via worker-info), not compile
                     ;; this needs to be in base module
                     (and default? build-worker?)
@@ -321,6 +327,9 @@
       "globalThis.goog = goog;\n"
       "globalThis.shadow$provide = {};"
 
+
+      "globalThis.shadow_esm_import = function(x) { return import(x.startsWith(\"./\") ? \".\" + x : x); }\n"
+
       "let $CLJS = globalThis.$CLJS = globalThis;"
       (slurp (io/resource "shadow/boot/esm.js"))
 
@@ -352,7 +361,7 @@
       polyfill-js
       "const $jscomp = {};\n")))
 
-(defn setup-imports [{::build/keys [mode] :as state}]
+(defn setup-imports [state]
   (update state :build-modules
     (fn [modules]
       (->> modules
@@ -374,7 +383,13 @@
 
                  (-> mod
                      (update :module-externs set/union externs)
-                     (update :prepend str-prepend (str imports "\n"))))))
+                     (update :prepend str-prepend (str imports "\n"))
+                     (cond->
+                       ;; only create shadow_esm_import if shadow.esm was required anywhere
+                       ;; needs to be created in all modules since it must be module local
+                       (get-in state [:sym->id 'shadow.esm])
+                       (update :prepend str "const shadow_esm_import = function(x) { return import(x) };\n"))
+                     ))))
            (vec)))))
 
 ;; in dev all imports must happen in the prepend

src/main/shadow/esm.cljs

@@ -0,0 +1,18 @@
+(ns shadow.esm)
+
+;; workaround until we can tell the closure-compiler to not rewrite
+;; a dynamic import(). we just want to keep it as is to import "foreign"
+;; code dynamically at runtime.
+;; FIXME: can't use import as name apparantly?
+;;
+;; (ns foo (:require [shadow.esm :refer (import)]))
+;; (defn init []
+;;   (js/console.log (import "./b.js")))
+;; ------------------------- ^------------------------------------------------------
+;; Error in phase :compilation
+;; Arguments to import must be quoted. Offending spec: ./b.js at line 10 demo / esm/a.cljs
+;; --------------------------------------------------------------------------------
+(defn dynamic-import
+  "dynamic import(path) where path is relative to the :output-dir of the build"
+  [what]
+  (js/shadow_esm_import what))