[ruby/irb] Handle long inspect and control character in prompt

string
(https://github.com/ruby/irb/pull/528)

* Handle long inspect and control characters in prompt string

* Add constants for prompt truncate length, omission and replace pattern

* Simply compare string instead of regexp in prompt truncation test

lib/irb.rb

@@ -463,6 +463,10 @@ module IRB
     # be parsed as :assign and echo will be suppressed, but the latter is
     # parsed as a :method_add_arg and the output won't be suppressed
 
+    PROMPT_MAIN_TRUNCATE_LENGTH = 32
+    PROMPT_MAIN_TRUNCATE_OMISSION = '...'.freeze
+    CONTROL_CHARACTERS_PATTERN = "\x00-\x1F".freeze
+
     # Creates a new irb session
     def initialize(workspace = nil, input_method = nil)
       @context = Context.new(self, workspace, input_method)
@@ -775,6 +779,15 @@ module IRB
       end
     end
 
+    def truncate_prompt_main(str) # :nodoc:
+      str = str.tr(CONTROL_CHARACTERS_PATTERN, ' ')
+      if str.size <= PROMPT_MAIN_TRUNCATE_LENGTH
+        str
+      else
+        str[0, PROMPT_MAIN_TRUNCATE_LENGTH - PROMPT_MAIN_TRUNCATE_OMISSION.size] + PROMPT_MAIN_TRUNCATE_OMISSION
+      end
+    end
+
     def prompt(prompt, ltype, indent, line_no) # :nodoc:
       p = prompt.dup
       p.gsub!(/%([0-9]+)?([a-zA-Z])/) do
@@ -782,9 +795,9 @@ module IRB
         when "N"
           @context.irb_name
         when "m"
-          @context.main.to_s
+          truncate_prompt_main(@context.main.to_s)
         when "M"
-          @context.main.inspect
+          truncate_prompt_main(@context.main.inspect)
         when "l"
           ltype
         when "i"

test/irb/test_context.rb

@@ -656,6 +656,23 @@ module TestIRB
       $VERBOSE = verbose
     end
 
+    def test_prompt_main_escape
+      irb = IRB::Irb.new(IRB::WorkSpace.new("main\a\t\r\n"))
+      assert_equal("irb(main    )>", irb.prompt('irb(%m)>', nil, 1, 1))
+    end
+
+    def test_prompt_main_inspect_escape
+      main = Struct.new(:inspect).new("main\\n\nmain")
+      irb = IRB::Irb.new(IRB::WorkSpace.new(main))
+      assert_equal("irb(main\\n main)>", irb.prompt('irb(%M)>', nil, 1, 1))
+    end
+
+    def test_prompt_main_truncate
+      irb = IRB::Irb.new(IRB::WorkSpace.new("a" * 100))
+      assert_equal('irb(aaaaaaaaaaaaaaaaaaaaaaaaaaaaa...)>', irb.prompt('irb(%m)>', nil, 1, 1))
+      assert_equal('irb("aaaaaaaaaaaaaaaaaaaaaaaaaaaa...)>', irb.prompt('irb(%M)>', nil, 1, 1))
+    end
+
     def test_lineno
       input = TestInputMethod.new([
         "\n",