Fix *flush-on-newline* behavior

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 ## UNRELEASED
 
+- Fix `*flush-on-newline*` behavior
+
+  If `*flush-on-newline` is set to `true` (the default), like clojure.pprint, pp now only flushes after pretty-printing the entire form, instead of flushing after every newline.
+
 - Add Maven (Clojars) release
 - Add ClojureScript support
 - Add explicit (unit tested) Babashka support

src/me/flowthing/pp.cljc

@@ -64,9 +64,7 @@
     "Write a newline into the underlying java.io.Writer.
 
     Resets the number of characters allotted to the current line to
-    zero.
-
-    If *flush-on-newline* is true, flushes the underlying writer."))
+    zero."))
 
 (defn ^:private write-into
   "Given a writer (java.io.Writer or cljs.core.IWriter) and a string,
@@ -103,10 +101,6 @@
         (- max-width @c))
       (nl [_]
         (write-into writer "\n")
-
-        (when *flush-on-newline*
-          #?(:clj (.flush ^java.io.Writer writer) :cljs (-flush writer)))
-
         (vreset! c 0)
         nil))))
 
@@ -584,7 +578,9 @@
             (do
               (print-dup x writer)
               (.write ^java.io.Writer writer "\n"))
-            (pp writer)))
+            (pp writer))
+
+          (when *flush-on-newline* (.flush ^java.io.Writer writer)))
 
         :cljs
         (if writer
@@ -598,4 +594,5 @@
           (let [sb (goog.string.StringBuffer.)
                 writer (StringBufferWriter. sb)]
             (pp writer)
-            (-> sb str string-print)))))))
+            (-> sb str string-print)
+            (when *flush-on-newline* (-flush writer))))))))

test/me/flowthing/pp_flush_test.clj

@@ -0,0 +1,32 @@
+(ns me.flowthing.pp-flush-test
+  (:require [clojure.test :refer [deftest is testing]]
+            [me.flowthing.pp :as sut])
+  (:import (java.io BufferedWriter StringWriter)))
+
+(defn ^:private flush-observing-writer
+  [writer]
+  (let [a (atom 0)]
+    [(proxy [BufferedWriter] [writer]
+       (flush []
+         (proxy-super flush)
+         (swap! a inc)))
+     a]))
+
+(deftest flush-on-newline
+  (testing "Does not flush after printing if *flush-on-newline* is nil"
+    (let [sw (StringWriter.)
+          [writer a] (flush-observing-writer sw)]
+      (binding [*flush-on-newline* nil]
+        (sut/pprint writer {:a 1 :b 2 :c 3 :d 4} {:max-width 10}))
+      (is (= [0 ""] [@a (str sw)]))))
+
+  (testing "Only flushes after printing the entire top-level form if *flush-on-newline* is true"
+    ;; So when pretty-printing, *flush-on-newline* doesn't actually flush on
+    ;; newline, only after printing the entire top-level form.
+    (let [sw (StringWriter.)
+          [writer a] (flush-observing-writer sw)]
+      (binding [*flush-on-newline* true]
+        (sut/pprint writer {:a 1 :b 2 :c 3 :d 4} {:max-width 10})
+        (sut/pprint writer {:a 1 :b 2 :c 3 :d 4} {:max-width 10}))
+      (is (= [2 "{:a 1,\n :b 2,\n :c 3,\n :d 4}\n{:a 1,\n :b 2,\n :c 3,\n :d 4}\n"]
+            [@a (str sw)])))))