Add initial pass

.gitignore

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+.cpcache
+/delegate.jar

deps.edn

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+{:paths ["src"]
+ :deps
+ {org.clojure/clojurescript {:mvn/version "1.10.597"}}
+ :aliases {:pack
+           {:extra-deps
+            {pack/pack.alpha
+             {:git/url "https://github.com/juxt/pack.alpha.git"
+              :sha "60cdf0e75efc988b893eafe726ccdf0d5a5a6067"}}
+            :main-opts ["-m"]}}}

jar.sh

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+clojure -A:pack \
+          mach.pack.alpha.skinny \
+          --no-libs \
+          --project-path delegate.jar

mvn.sh

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+mvn deploy:deploy-file \
+      -Dfile=delegate.jar \
+      -DrepositoryId=clojars \
+      -Durl=https://clojars.org/repo \
+      -DpomFile=pom.xml

pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>io.dominic</groupId>
+  <artifactId>delegating-repl</artifactId>
+  <version>0.0.2</version>
+  <name>delegating-repl</name>
+  <dependencies>
+    <dependency>
+      <groupId>org.clojure</groupId>
+      <artifactId>clojure</artifactId>
+      <version>1.10.1</version>
+    </dependency>
+    <dependency>
+      <groupId>org.clojure</groupId>
+      <artifactId>clojurescript</artifactId>
+      <version>1.10.597</version>
+    </dependency>
+  </dependencies>
+  <build>
+    <sourceDirectory>src</sourceDirectory>
+  </build>
+  <repositories>
+    <repository>
+      <id>clojars</id>
+      <url>https://repo.clojars.org/</url>
+    </repository>
+  </repositories>
+</project>

src/io/dominic/delegating_repl/core.clj

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+(ns io.dominic.delegating-repl.core
+  (:require
+    [cljs.repl :as repl]
+    [clojure.java.shell :as sh]))
+
+(defrecord DelegatingEnv [delegate]
+  repl/IJavaScriptEnv
+  (-setup [this opts]
+    (let [result (repl/-setup delegate opts)
+          !exec (future (apply sh/sh (get opts :launch-command)))]
+      (try
+        ;; Check command didn't fail within 1s, indicating some obvious
+        ;; failure.
+        (when-let [{:keys [exit out err]} (deref !exec 1000 nil)]
+          (when (pos? exit)
+            (println "Failed to run launch-command: "
+                     (get opts :launch-command))
+            (println "STDOUT:\n" (String. out))
+            (println "STDERR:\n" (String. err))))
+        (catch Throwable t
+          (println "Failed to run launch-command: "
+                   (get opts :launch-command))
+          (.printStackTrace t)))
+      result))
+  (-evaluate [this filename line js]
+    (repl/-evaluate delegate filename line js))
+  (-load [this provides url]
+    (repl/-load delegate provides url))
+  (-tear-down [this]
+    (repl/-tear-down delegate))
+  repl/IReplEnvOptions
+  (-repl-options [this]
+    ;; TODO: Look into
+    #_{:browser-repl true
+     :repl-requires
+     '[[clojure.browser.repl] [clojure.browser.repl.preload]]
+     :cljs.cli/commands
+     {:groups {::repl {:desc "browser REPL options"}}
+      :init
+      {["-H" "--host"]
+       {:group ::repl :fn #(assoc-in %1 [:repl-env-options :host] %2)
+        :arg "address"
+        :doc "Address to bind"}
+       ["-p" "--port"]
+       {:group ::repl :fn #(assoc-in %1 [:repl-env-options :port] (Integer/parseInt %2))
+        :arg "number"
+        :doc "Port to bind"}}}}
+    (repl/-repl-options delegate))
+  repl/IParseStacktrace
+  (-parse-stacktrace [this st err opts]
+    (repl/-parse-stacktrace delegate st err opts))
+  repl/IGetError
+  (-get-error [this e env opts]
+    (repl/-get-error delegate e env opts)))
+
+(defn repl-env
+  [& {:as compiler-opts}]
+  (let [{repl-env-f :io.dominic.delegating-repl/repl-env}
+        compiler-opts
+        repl-env (apply (requiring-resolve repl-env-f)
+                        (apply concat compiler-opts))]
+    (merge (->DelegatingEnv repl-env)
+           ;; Adds any keys that things might be poking at.
+           repl-env)))