[ruby/reline] Fallback to 256color if COLORTERM != truecolor

(https://github.com/ruby/reline/pull/604)

* Fallback to 256color if COLORTERM != truecolor

* Add Reline::Face.force_truecolor to force truecolor without COLORTERM env

https://github.com/ruby/reline/commit/090e1e4df0

1 files changed, 42 insertions, 0 deletions

diff --git a/lib/reline/face.rb b/lib/reline/face.rb
index b78f3b1ca5..e18ec957e8 100644
--- a/lib/reline/face.rb
+++ b/lib/reline/face.rb
@@ -74,6 +74,13 @@ class Reline::Face
       @definition[name] = values
     end
 
+    def reconfigure
+      @definition.each_value do |values|
+        values.delete(:escape_sequence)
+        values[:escape_sequence] = format_to_sgr(values.to_a).freeze
+      end
+    end
+
     def [](name)
       @definition.dig(name, :escape_sequence) or raise ArgumentError, "unknown face: #{name}"
     end
@@ -82,6 +89,14 @@ class Reline::Face
 
     def sgr_rgb(key, value)
       return nil unless rgb_expression?(value)
+      if Reline::Face.truecolor?
+        sgr_rgb_truecolor(key, value)
+      else
+        sgr_rgb_256color(key, value)
+      end
+    end
+
+    def sgr_rgb_truecolor(key, value)
       case key
       when :foreground
         "38;2;"
@@ -90,6 +105,24 @@ class Reline::Face
       end + value[1, 6].scan(/../).map(&:hex).join(";")
     end
 
+    def sgr_rgb_256color(key, value)
+      # 256 colors are
+      # 0..15: standard colors, hight intensity colors
+      # 16..232: 216 colors (R, G, B each 6 steps)
+      # 233..255: grayscale colors (24 steps)
+      # This methods converts rgb_expression to 216 colors
+      rgb = value[1, 6].scan(/../).map(&:hex)
+      # Color steps are [0, 95, 135, 175, 215, 255]
+      r, g, b = rgb.map { |v| v <= 95 ? v / 48 : (v - 35) / 40 }
+      color = (16 + 36 * r + 6 * g + b)
+      case key
+      when :foreground
+        "38;5;#{color}"
+      when :background
+        "48;5;#{color}"
+      end
+    end
+
     def format_to_sgr(ordered_values)
       sgr = "\e[" + ordered_values.map do |key_value|
         key, value = key_value
@@ -124,6 +157,15 @@ class Reline::Face
 
   private_constant :SGR_PARAMETERS, :Config
 
+  def self.truecolor?
+    @force_truecolor || %w[truecolor 24bit].include?(ENV['COLORTERM'])
+  end
+
+  def self.force_truecolor
+    @force_truecolor = true
+    @configs&.each_value(&:reconfigure)
+  end
+
   def self.[](name)
     @configs[name]
   end