Pry: don't strip newlines from multi-line exprs

Fix issue #704 (newlines are stripped from inside pasted strings)

Also, make sure that other literals (system calls, regexps) also comply
this rule.

Reviewed-by: Conrad Irwin <conrad.irwin@gmail.com>

lib/pry/pry_instance.rb

@@ -297,7 +297,7 @@ class Pry
     inject_sticky_locals!
     begin
       if !process_command_safely(line.lstrip)
-        @eval_string << "#{line.chomp}\n" unless line.empty?
+        @eval_string << "#{line.chomp}\n" if !line.empty? || !@eval_string.empty?
       end
     rescue RescuableException => e
       self.last_exception = e

spec/pry_spec.rb

@@ -109,10 +109,6 @@ describe Pry do
         pry_eval(o, "self").should == o
       end
 
-      it 'should work with multi-line input' do
-        mock_pry("x = ", "1 + 4").should =~ /5/
-      end
-
       it 'should define a nested class under Hello and not on top-level or Pry' do
         mock_pry(Pry.binding_for(Hello), "class Nested", "end")
         Hello.const_defined?(:Nested).should == true
@@ -126,10 +122,6 @@ describe Pry do
         mock_pry("x = 5;").should == ""
       end
 
-      it 'should suppress output if input ends in a ";" (multi-line)' do
-        mock_pry("def self.blah", ":test", "end;").should == ""
-      end
-
       it 'should be able to evaluate exceptions normally' do
         was_called = false
         mock_pry("RuntimeError.new", :exception_handler => proc{ was_called = true })
@@ -147,6 +139,53 @@ describe Pry do
         # SIGTERM
         lambda { mock_pry("raise SignalException.new(15)") }.should.raise SignalException
       end
+
+      describe "multi-line input" do
+        it "works" do
+          mock_pry('x = ', '1 + 4').should =~ /5/
+        end
+
+        it 'should suppress output if input ends in a ";" (multi-line)' do
+          mock_pry('def self.blah', ':test', 'end;').should == ''
+        end
+
+        describe "newline stripping from an empty string" do
+          it "with double quotes" do
+            mock_pry('"', '"').should =~ %r|"\\n"|
+            mock_pry('"', "\n", "\n", "\n", '"').should =~ %r|"\\n\\n\\n\\n"|
+          end
+
+          it "with single quotes" do
+            mock_pry("'", "'").should =~ %r|"\\n"|
+            mock_pry("'", "\n", "\n", "\n", "'").should =~ %r|"\\n\\n\\n\\n"|
+          end
+
+          it "with fancy delimiters" do
+            mock_pry('%(', ')').should =~ %r|"\\n"|
+            mock_pry('%|', "\n", "\n", '|').should =~ %r|"\\n\\n\\n"|
+            mock_pry('%q[', "\n", "\n", ']').should =~ %r|"\\n\\n\\n"|
+          end
+        end
+
+        describe "newline stripping from an empty regexp" do
+          it "with regular regexp delimiters" do
+            mock_pry('/', '/').should =~ %r{/\n/}
+          end
+
+          it "with fancy delimiters" do
+            mock_pry('%r{', "\n", "\n", '}').should =~ %r{/\n\n\n/}
+            mock_pry('%r<', "\n", '>').should =~ %r{/\n\n/}
+          end
+        end
+
+        describe "newline from an empty heredoc" do
+          it "works" do
+            mock_pry('<<HERE', 'HERE').should =~ %r|""|
+            mock_pry("<<'HERE'", "\n", 'HERE').should =~ %r|"\\n"|
+            mock_pry("<<-'HERE'", "\n", "\n", 'HERE').should =~ %r|"\\n\\n"|
+          end
+        end
+      end
     end
 
     describe "repl" do