Improve reify error messages (#1352)

Co-authored-by: Crispin Wellington <retrogradeorbit@gmail.com>

CHANGELOG.md

@@ -9,6 +9,13 @@ A preview of the next release can be installed from
 
 Check out our new project: [bbin](https://github.com/babashka/bbin): install any Babashka script or project with one command.
 
+- Throw exception on attempt to reify multiple interfaces
+- Allow java.lang.Object reify with empty methods
+
+## 0.9.162 (2022-09-04)
+
+Check out our new project: [bbin](https://github.com/babashka/bbin): install any Babashka script or project with one command.
+
 - [#1343](https://github.com/babashka/babashka/issues/1343): Fix postgres feature
 - [#1345](https://github.com/babashka/babashka/issues/1345): add `javax.net.ssl.SSLException` and `java.net.SocketTimeoutException` classes ([@lread](https://github.com/lread))
 - Fix `satisfies?` with marker protocol (no methods)

deps.edn

@@ -16,7 +16,8 @@
          "babashka.nrepl/src"
          "depstar/src" "process/src"
          "deps.clj/src" "deps.clj/resources"
-         "resources" "sci/resources"],
+         "resources" "sci/resources"
+         "reify/src"],
  :deps {org.clojure/clojure {:mvn/version "1.11.1"},
         org.babashka/sci {:local/root "sci"}
         org.babashka/babashka.impl.reify {:mvn/version "0.1.2"}

reify/src/babashka/impl/reify2.clj

@@ -45,8 +45,26 @@
       (invoke [this a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 a14 a15 a16 a17 a18 a19 a20] (invoke-fn this a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 a14 a15 a16 a17 a18 a19 a20))
       (applyTo [this arglist] (apply-fn this arglist)))))
 
+(defn reify-object [m]
+  (let [methods (:methods m)
+        toString-fn (or (get methods 'toString)
+                        (fn [this]
+                          (str
+                           (.getName (.getClass this))
+                           "@"
+                           (Integer/toHexString (.hashCode this)))))]
+    (reify
+      sci.impl.types.IReified
+      (getMethods [_] (:methods m))
+      (getInterfaces [_] (:interfaces m))
+      (getProtocols [_] (:protocols m))
+      java.lang.Object
+      (toString [this] (toString-fn this)))))
+
 (defmacro gen-reify-fn []
   `(fn [~'m]
+     (when (> (count (:interfaces ~'m)) 1)
+       (throw (UnsupportedOperationException. "babashka reify only supports implementing a single interface")))
      (if (empty? (:interfaces ~'m))
        (reify
          sci.impl.types.IReified
@@ -55,19 +73,12 @@
          (getProtocols [_] (:protocols ~'m)))
        (case (.getName ~(with-meta `(first (:interfaces ~'m))
                           {:tag 'Class}))
-         "java.lang.Object"
-         (reify
-           java.lang.Object
-           (toString [~'this]
-             ((method-or-bust (:methods ~'m) (quote ~'toString)) ~'this))
-           sci.impl.types.IReified
-           (getMethods [_] (:methods ~'m))
-           (getInterfaces [_] (:interfaces ~'m))
-           (getProtocols [_] (:protocols ~'m)))
          ~@(mapcat identity
                    (cons
                     ["clojure.lang.IFn"
-                     `(reify-ifn ~'m)]
+                     `(reify-ifn ~'m)
+                     "java.lang.Object"
+                     `(reify-object ~'m)]
                     (for [i interfaces]
                       (let [in (.getName ^Class i)]
                         [in

test/babashka/reify_test.clj

@@ -51,6 +51,11 @@
 ]")))))
 
 (deftest reify-object
+  (testing "empty methods"
+    (is (clojure.string/starts-with?
+         (bb nil "
+(str (reify Object))")
+         "babashka.impl.reify")))
   (testing "toString"
     (is (= ":foo"
            (bb nil "
@@ -114,3 +119,12 @@
                    iter (reify java.util.function.Consumer (accept [_ x] (vswap! res conj x))))
                   (= [true :a :b :c] @res))]
     (is (true? (bb nil prog)))))
+
+(deftest reify-multiple-interfaces-test
+  (testing "throws exception"
+    (is (thrown?
+         clojure.lang.ExceptionInfo
+         (bb nil "
+(reify
+  java.lang.Object (toString [_] \"foo\")
+  clojure.lang.Seqable (seq [_] '(1 2 3)))")))))