[ruby/irb] Add doc about "echo on assignment"

https://github.com/ruby/irb/commit/5af637b3c1

doc/irb/irb.rd.ja

@@ -51,6 +51,12 @@ irbの使い方は, Rubyさえ知っていればいたって簡単です. 基本
 		    オブジェクトの作成方法を 0 から 3 のいずれかに設定する.
   --echo	    実行結果を表示する(デフォルト).
   --noecho	    実行結果を表示しない.
+  --echo-on-assignment
+                    代入時に実行結果を表示する.
+  --noecho-on-assignment
+                    代入時に実行結果を表示しない.
+  --truncate-echo-on-assignment
+                    代入時に省略された実行結果を表示する(デフォルト).
   --inspect	    結果出力にinspectを用いる.
   --noinspect	    結果出力にinspectを用いない.
   --singleline      シングルラインエディタを利用する.

lib/irb.rb

@@ -64,6 +64,12 @@ require_relative "irb/easter-egg"
 #                       when new workspace was created
 #     --echo            Show result (default)
 #     --noecho          Don't show result
+#     --echo-on-assignment
+#                       Show result on assignment
+#     --noecho-on-assignment
+#                       Don't show result on assignment
+#     --truncate-echo-on-assignment
+#                       Show truncated result on assignment (default)
 #     --inspect         Use `inspect' for output
 #     --noinspect       Don't use inspect for output
 #     --multiline       Use multiline editor module

lib/irb/context.rb

@@ -274,6 +274,18 @@ module IRB
     #     IRB.CurrentContext.echo_on_assignment = true
     #     a = "omg" * 10
     #     #=> omgomgomgomgomgomgomgomgomgomg
+    #
+    # To set the behaviour of showing on assignment in irb:
+    #
+    #     IRB.conf[:ECHO_ON_ASSIGNMENT] = :truncate or true or false
+    #
+    # or
+    #
+    #     irb_context.echo_on_assignment = :truncate or true or false
+    #
+    # or
+    #
+    #     IRB.CurrentContext.echo_on_assignment = :truncate or true or false
     attr_accessor :echo_on_assignment
     # Whether a newline is put before multiline output.
     #

lib/irb/lc/help-message

@@ -22,6 +22,12 @@ Usage:  irb.rb [options] [programfile] [arguments]
                     when new workspace was created
   --echo            Show result (default)
   --noecho          Don't show result
+  --echo-on-assignment
+                    Show result on assignment
+  --noecho-on-assignment
+                    Don't show result on assignment
+  --truncate-echo-on-assignment
+                    Show truncated result on assignment (default)
   --inspect         Use `inspect' for output
   --noinspect       Don't use inspect for output
   --multiline       Use multiline editor module

man/irb.1

@@ -112,6 +112,16 @@ Show result (default).
 Don't show result.
 .Pp
 .Pp
+.It Fl -echo-on-assignment
+Show result on assignment.
+.Pp
+.It Fl -noecho-on-assignment
+Don't show result on assignment.
+.Pp
+.It Fl -truncate-echo-on-assignment
+Show truncated result on assignment (default).
+.Pp
+.Pp
 .It Fl -colorize
 Use colorization.
 .Pp