Show-source should not raise error even if line_no is wrong (#1145)

Fix SourceFinder to handle wrong line_no case, such as:
- line_no passed to eval is wrong
- File edited after load

Author: tompng

lib/irb/source_finder.rb

@@ -29,10 +29,13 @@ def file_content
 
       def colorized_content
         if !binary_file? && file_exist?
-          end_line = find_end
           # To correctly colorize, we need to colorize full content and extract the relevant lines.
-          colored = IRB::Color.colorize_code(file_content)
-          colored.lines[@line - 1...end_line].join
+          colored_lines = IRB::Color.colorize_code(file_content).lines
+
+          # Handle wrong line number case: line_no passed to eval is wrong, file is edited after load, etc
+          return if colored_lines.size < @line
+
+          colored_lines[@line - 1...find_end].join
         elsif @ast_source
           IRB::Color.colorize_code(@ast_source)
         end

test/irb/command/test_show_source.rb

@@ -376,7 +376,7 @@ def test_show_source_shows_binary_source
       assert_match(%r[Defined in binary file:.+io/console], out)
     end
 
-    def test_show_source_method_overrided
+    def test_show_source_method_overridden
       write_ruby <<~RUBY
         class Request
           def method; 'POST'; end
@@ -393,6 +393,23 @@ def path; '/'; end
       assert_match(%r[#{@ruby_file.to_path}:3\s+def path; '/'; end], out)
     end
 
+    def test_show_source_with_wrong_line
+      write_ruby <<~RUBY.chomp
+        eval 'def foo; end', binding, __FILE__, 4 # Line 4 doesn't exist
+        binding.irb if
+        def bar; end # Line 3
+      RUBY
+
+      out = run_ruby_file do
+        type "show_source foo"
+        type "show_source bar"
+        type "exit"
+      end
+
+      assert_match(%r[#{@ruby_file.to_path}:4\s+Source not available], out)
+      assert_match(%r[#{@ruby_file.to_path}:3\s+def bar; end], out)
+    end
+
     def test_show_source_with_constant_lookup
       write_ruby <<~RUBY
         X = 1