Handle very long lines

lib/error_highlight/formatter.rb

@@ -1,15 +1,66 @@
 module ErrorHighlight
   class DefaultFormatter
+    MIN_SNIPPET_WIDTH = 20
+
     def self.message_for(spot)
       # currently only a one-line code snippet is supported
-      if spot[:first_lineno] == spot[:last_lineno]
-        indent = spot[:snippet][0...spot[:first_column]].gsub(/[^\t]/, " ")
-        marker = indent + "^" * (spot[:last_column] - spot[:first_column])
+      return "" unless spot[:first_lineno] == spot[:last_lineno]
+
+      snippet      = spot[:snippet]
+      first_column = spot[:first_column]
+      last_column  = spot[:last_column]
+      ellipsis     = "..."
+
+      # truncate snippet to fit in the viewport
+      if snippet_max_width && snippet.size > snippet_max_width
+        available_width = snippet_max_width - ellipsis.size
+        center          = first_column - snippet_max_width / 2
+
+        visible_start  = last_column < available_width ? 0 : [center, 0].max
+        visible_end    = visible_start + snippet_max_width
+        visible_start  = snippet.size - snippet_max_width if visible_end > snippet.size
+
+        prefix = visible_start.positive?    ? ellipsis : ""
+        suffix = visible_end < snippet.size ? ellipsis : ""
 
-        "\n\n#{ spot[:snippet] }#{ marker }"
-      else
-        ""
+        snippet = prefix + snippet[(visible_start + prefix.size)...(visible_end - suffix.size)] + suffix
+        snippet << "\n" unless snippet.end_with?("\n")
+
+        first_column -= visible_start
+        last_column  = [last_column - visible_start, snippet.size - 1].min
       end
+
+      indent = snippet[0...first_column].gsub(/[^\t]/, " ")
+      marker = indent + "^" * (last_column - first_column)
+
+      "\n\n#{ snippet }#{ marker }"
+    end
+
+    def self.snippet_max_width
+      return if Ractor.current[:__error_highlight_max_snippet_width__] == :disabled
+
+      Ractor.current[:__error_highlight_max_snippet_width__] ||= terminal_width
+    end
+
+    def self.snippet_max_width=(width)
+      return Ractor.current[:__error_highlight_max_snippet_width__] = :disabled if width.nil?
+
+      width = width.to_i
+
+      if width < MIN_SNIPPET_WIDTH
+        warn "'snippet_max_width' adjusted to minimum value of #{MIN_SNIPPET_WIDTH}."
+        width = MIN_SNIPPET_WIDTH
+      end
+
+      Ractor.current[:__error_highlight_max_snippet_width__] = width
+    end
+
+    def self.terminal_width
+      # lazy load io/console, so it's not loaded when snippet_max_width is set
+      require "io/console"
+      STDERR.winsize[1] if STDERR.tty?
+    rescue LoadError, NoMethodError, SystemCallError
+      # do not truncate when window size is not available
     end
   end
 

test/test_error_highlight.rb

@@ -5,6 +5,8 @@
 require "tempfile"
 
 class ErrorHighlightTest < Test::Unit::TestCase
+  ErrorHighlight::DefaultFormatter.snippet_max_width = 80
+
   class DummyFormatter
     def self.message_for(corrections)
       ""
@@ -1285,6 +1287,136 @@ def test_no_final_newline
     end
   end
 
+  def test_errors_on_small_terminal_window_at_the_end
+    assert_error_message(NoMethodError, <<~END) do
+undefined method `time' for #{ ONE_RECV_MESSAGE }
+
+...0000000000000000000000000000000000000000000000000000000000000000 + 1.time {}
+                                                                       ^^^^^
+    END
+
+    100000000000000000000000000000000000000000000000000000000000000000000000000000 + 1.time {}
+    end
+  end
+
+  def test_errors_on_small_terminal_window_at_the_beginning
+    assert_error_message(NoMethodError, <<~END) do
+undefined method `time' for #{ ONE_RECV_MESSAGE }
+
+      1.time { 10000000000000000000000000000000000000000000000000000000000000...
+       ^^^^^
+    END
+
+      1.time { 100000000000000000000000000000000000000000000000000000000000000000000000000000 }
+
+    end
+  end
+
+  def test_errors_on_small_terminal_window_at_the_middle_near_beginning
+    assert_error_message(NoMethodError, <<~END) do
+undefined method `time' for #{ ONE_RECV_MESSAGE }
+
+    100000000000000000000000000000000000000 + 1.time { 1000000000000000000000...
+                                               ^^^^^
+    END
+
+    100000000000000000000000000000000000000 + 1.time { 100000000000000000000000000000000000000 }
+    end
+  end
+
+  def test_errors_on_small_terminal_window_at_the_middle
+    assert_error_message(NoMethodError, <<~END) do
+undefined method `time' for #{ ONE_RECV_MESSAGE }
+
+...000000000000000000000000000000000 + 1.time { 10000000000000000000000000000...
+                                        ^^^^^
+    END
+
+    10000000000000000000000000000000000000000000000000000000000000000000000 + 1.time { 1000000000000000000000000000000 }
+    end
+  end
+
+  def test_errors_on_extremely_small_terminal_window
+    custom_max_width = 30
+    original_max_width = ErrorHighlight::DefaultFormatter.snippet_max_width
+
+    ErrorHighlight::DefaultFormatter.snippet_max_width = custom_max_width
+
+    assert_error_message(NoMethodError, <<~END) do
+undefined method `time' for #{ ONE_RECV_MESSAGE }
+
+...00000000 + 1.time { 1000...
+               ^^^^^
+    END
+
+      100000000000000 + 1.time { 100000000000000 }
+    end
+  ensure
+    ErrorHighlight::DefaultFormatter.snippet_max_width = original_max_width
+  end
+
+  def test_errors_on_terminal_window_smaller_than_min_width
+    custom_max_width = 5
+    original_max_width = ErrorHighlight::DefaultFormatter.snippet_max_width
+
+    ErrorHighlight::DefaultFormatter.snippet_max_width = custom_max_width
+
+    assert_error_message(NoMethodError, <<~END) do
+undefined method `time' for #{ ONE_RECV_MESSAGE }
+
+...000 + 1.time {...
+          ^^^^^
+    END
+
+    100000000000000 + 1.time { 100000000000000 }
+    end
+  ensure
+    ErrorHighlight::DefaultFormatter.snippet_max_width = original_max_width
+  end
+
+  def test_errors_on_terminal_window_when_truncation_is_disabled
+    custom_max_width = nil
+    original_max_width = ErrorHighlight::DefaultFormatter.snippet_max_width
+
+    ErrorHighlight::DefaultFormatter.snippet_max_width = custom_max_width
+
+    assert_error_message(NoMethodError, <<~END) do
+undefined method `time' for #{ ONE_RECV_MESSAGE }
+
+      10000000000000000000000000000000000000000000000000000000000000000000000 + 1.time { 1000000000000000000000000000000 }
+                                                                                 ^^^^^
+    END
+
+      10000000000000000000000000000000000000000000000000000000000000000000000 + 1.time { 1000000000000000000000000000000 }
+    end
+  ensure
+    ErrorHighlight::DefaultFormatter.snippet_max_width = original_max_width
+  end
+
+  def test_errors_on_small_terminal_window_when_larger_than_viewport
+    assert_error_message(NoMethodError, <<~END) do
+undefined method `timessssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss!' for #{ ONE_RECV_MESSAGE }
+
+      1.timesssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss...
+       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+    END
+
+      1.timessssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss!
+    end
+  end
+
+  def test_errors_on_small_terminal_window_when_exact_size_of_viewport
+    assert_error_message(NoMethodError, <<~END) do
+undefined method `timessssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss!' for #{ ONE_RECV_MESSAGE }
+
+      1.timessssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss!...
+       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+    END
+
+      1.timessssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss! * 1000
+    end
+  end
+
   def test_simulate_funcallv_from_embedded_ruby
     assert_error_message(NoMethodError, <<~END) do
 undefined method `foo' for #{ NIL_RECV_MESSAGE }