Don't blow up on unresolvable pprint functions

First try to require their namespace and resolve them, afterwards
fallback to a safe default.

Author: bbatsov

src/cider/nrepl/middleware/pprint.clj

@@ -18,10 +18,17 @@
 ;; TODO: Remove this middleware (or make it a no-op).
 
 (defn- resolve-pprint-fn
-  [sym]
-  (if-let [pp-fn (-> sym u/as-sym find-var)]
-    pp-fn
-    (throw (IllegalArgumentException. (format "%s is not resolvable to a var" sym)))))
+  "Resolve a namespaced symbol to a printer var. Returns the var or nil if
+  the argument is nil or not resolvable."
+  [var-sym]
+  (when-let [var-sym (and var-sym (symbol var-sym))]
+    (try
+      (require (symbol (namespace var-sym)))
+      (resolve var-sym)
+      (catch Exception ex
+        (nrepl.misc/log ex "Couldn't resolve printer function" var-sym)
+        (require 'cider.nrepl.pprint)
+        (resolve 'cider.nrepl.pprint/pprint)))))
 
 (defn handle-pprint-fn
   [handler msg]

test/clj/cider/nrepl/middleware/format_test.clj

@@ -143,11 +143,9 @@
       (is (= "{:a 1, :b 2, :c 3}" formatted-edn))
       (is (= #{"done"} status))))
 
-  #_(testing "format-edn returns an error if the :pprint-fn is unresolvable"
-      (let [{:keys [err ex status] :as response} (session/message {:op "format-edn"
-                                                                   :edn "{:b 2 :c 3 :a 1}"
-                                                                   :pprint-fn "fake.nrepl.pprint/puget-pprint"})]
-        (is (.startsWith err "java.lang.IllegalArgumentException: No such namespace: fa"))
-        (is (= "class java.lang.IllegalArgumentException" ex))
-        (is (= #{"done" "format-edn-error"} status))
-        (is (:pp-stacktrace response)))))
+  (testing "format-edn returns fallbacks to a default printer if :pprint-fn is unresolvable"
+    (let [{:keys [formatted-edn status] :as response} (session/message {:op "format-edn"
+                                                                        :edn "{:b 2 :c 3 :a 1}"
+                                                                        :pprint-fn "fake.nrepl.pprint/puget-pprint"})]
+      (is (= "{:b 2, :c 3, :a 1}" formatted-edn))
+      (is (= #{"done"} status)))))