Add support for curly underline and separate underline color

Add support for a third color in face definition that controls
the underline and a 'c' attribute for curly underline (that takes
precedence over 'u' if both are specified)

Allow empty colors to mean default, so that `,,red+u` means the
same as `default,default,red+u`

Fixes #4138

5 files changed, 56 insertions, 24 deletions

diff --git a/src/commands.cc b/src/commands.cc
index e6fe6c92..1f5dcf7e 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -2384,8 +2384,8 @@ const CommandDesc set_face_cmd = {
     "facespec format is <fg color>[,<bg color>][+<attributes>][@<base>]\n"
     "colors are either a color name, rgb:######, or rgba:######## values.\n"
     "attributes is a combination of:\n"
-    "    u: underline, i: italic, b: bold, r: reverse,\n"
-    "    s: strikethrough, B: blink, d: dim,\n"
+    "    u: underline, c: curly underline, i: italic, b: bold,\n"
+    "    r: reverse, s: strikethrough, B: blink, d: dim,\n"
     "    f: final foreground, g: final background,\n"
     "    a: final attributes, F: same as +fga\n"
     "facespec can as well just be the name of another face.\n"
diff --git a/src/face.hh b/src/face.hh
index 798cd3f3..ce544116 100644
--- a/src/face.hh
+++ b/src/face.hh
@@ -9,18 +9,19 @@ namespace Kakoune
 
 enum class Attribute : int
 {
-    Normal        = 0,
-    Underline     = 1 << 1,
-    Reverse       = 1 << 2,
-    Blink         = 1 << 3,
-    Bold          = 1 << 4,
-    Dim           = 1 << 5,
-    Italic        = 1 << 6,
-    Strikethrough = 1 << 7,
-    FinalFg       = 1 << 8,
-    FinalBg       = 1 << 9,
-    FinalAttr     = 1 << 10,
-    Final         = FinalFg | FinalBg | FinalAttr
+    Normal         = 0,
+    Underline      = 1 << 1,
+    CurlyUnderline = 1 << 2,
+    Reverse        = 1 << 3,
+    Blink          = 1 << 4,
+    Bold           = 1 << 5,
+    Dim            = 1 << 6,
+    Italic         = 1 << 7,
+    Strikethrough  = 1 << 8,
+    FinalFg        = 1 << 9,
+    FinalBg        = 1 << 10,
+    FinalAttr      = 1 << 11,
+    Final          = FinalFg | FinalBg | FinalAttr
 };
 
 constexpr bool with_bit_ops(Meta::Type<Attribute>) { return true; }
@@ -30,11 +31,13 @@ struct Face
     Color fg = Color::Default;
     Color bg = Color::Default;
     Attribute attributes = Attribute::Normal;
+    Color underline = Color::Default;
 
     friend constexpr bool operator==(const Face& lhs, const Face& rhs)
     {
         return lhs.fg == rhs.fg and
                lhs.bg == rhs.bg and
+               lhs.underline == rhs.underline and
                lhs.attributes == rhs.attributes;
     }
 
@@ -45,7 +48,7 @@ struct Face
 
     friend constexpr size_t hash_value(const Face& val)
     {
-        return hash_values(val.fg, val.bg, val.attributes);
+        return hash_values(val.fg, val.bg, val.underline, val.attributes);
     }
 };
 
@@ -77,7 +80,8 @@ inline Face merge_faces(const Face& base, const Face& face)
                  choose(&Face::bg, Attribute::FinalBg),
                  face.attributes & Attribute::FinalAttr ? face.attributes :
                  base.attributes & Attribute::FinalAttr ? base.attributes :
-                 face.attributes | base.attributes };
+                 face.attributes | base.attributes,
+                 choose(&Face::underline, Attribute{0}) };
 }
 
 }
diff --git a/src/face_registry.cc b/src/face_registry.cc
index 638059ac..87d638e7 100644
--- a/src/face_registry.cc
+++ b/src/face_registry.cc
@@ -9,11 +9,12 @@ namespace Kakoune
 
 static FaceRegistry::FaceSpec parse_face(StringView facedesc)
 {
-    constexpr StringView invalid_face_error = "invalid face description, expected [<fg>][,<bg>][+<attr>][@base] or just [base]";
+    constexpr StringView invalid_face_error = "invalid face description, expected [<fg>][,<bg>[,<underline>]][+<attr>][@base] or just [base]";
     if (all_of(facedesc, [](char c){ return is_word(c); }) and not is_color_name(facedesc))
         return {Face{}, facedesc.str()};
 
     auto bg_it = find(facedesc, ',');
+    auto underline_it = bg_it == facedesc.end() ? bg_it : std::find(bg_it+1, facedesc.end(), ',');
     auto attr_it = find(facedesc, '+');
     auto base_it = find(facedesc, '@');
     if (bg_it != facedesc.end()
@@ -25,12 +26,19 @@ static FaceRegistry::FaceSpec parse_face(StringView facedesc)
 
     auto colors_end = std::min(attr_it, base_it);
 
+    auto parse_color = [](StringView spec) {
+        return spec.empty() ? Color::Default : str_to_color(spec);
+    };
+
     FaceRegistry::FaceSpec spec;
     auto& face = spec.face;
-    face.fg = colors_end != facedesc.begin() ?
-        str_to_color({facedesc.begin(), std::min(bg_it, colors_end)}) : Color::Default;
+    face.fg = parse_color({facedesc.begin(), std::min(bg_it, colors_end)});
     if (bg_it != facedesc.end())
-        face.bg = bg_it+1 != attr_it ? str_to_color({bg_it+1, colors_end}) : Color::Default;
+    {
+        face.bg = parse_color({bg_it+1, std::min(underline_it, colors_end)});
+        if (underline_it != facedesc.end())
+            face.underline = parse_color({underline_it+1, colors_end});
+    }
     if (attr_it != facedesc.end())
     {
         for (++attr_it; attr_it != base_it; ++attr_it)
@@ -38,6 +46,7 @@ static FaceRegistry::FaceSpec parse_face(StringView facedesc)
             switch (*attr_it)
             {
                 case 'u': face.attributes |= Attribute::Underline; break;
+                case 'c': face.attributes |= Attribute::CurlyUnderline; break;
                 case 'r': face.attributes |= Attribute::Reverse; break;
                 case 'b': face.attributes |= Attribute::Bold; break;
                 case 'B': face.attributes |= Attribute::Blink; break;
@@ -65,6 +74,7 @@ String to_string(Attribute attributes)
     struct Attr { Attribute attr; StringView name; }
     attrs[] {
         { Attribute::Underline, "u" },
+        { Attribute::CurlyUnderline, "c" },
         { Attribute::Reverse, "r" },
         { Attribute::Blink, "B" },
         { Attribute::Bold, "b" },
@@ -90,7 +100,7 @@ String to_string(Attribute attributes)
 
 String to_string(Face face)
 {
-    return format("{},{}{}", face.fg, face.bg, face.attributes);
+    return format("{},{},{}{}", face.fg, face.bg, face.underline, face.attributes);
 }
 
 Face FaceRegistry::operator[](StringView facedesc) const
diff --git a/src/json_ui.cc b/src/json_ui.cc
index 36c547ef..f5ae1f1f 100644
--- a/src/json_ui.cc
+++ b/src/json_ui.cc
@@ -57,8 +57,8 @@ String to_json(Attribute attributes)
 
 String to_json(Face face)
 {
-    return format(R"(\{ "fg": {}, "bg": {}, "attributes": {} })",
-                  to_json(face.fg), to_json(face.bg), to_json(face.attributes));
+    return format(R"(\{ "fg": {}, "bg": {}, "underline": {}, "attributes": {} })",
+                  to_json(face.fg), to_json(face.bg), to_json(face.underline), to_json(face.attributes));
 }
 
 String to_json(const DisplayAtom& atom)
diff --git a/src/terminal_ui.cc b/src/terminal_ui.cc
index 58d786c9..67b21e7f 100644
--- a/src/terminal_ui.cc
+++ b/src/terminal_ui.cc
@@ -223,7 +223,8 @@ void TerminalUI::Screen::set_face(const Face& face, Writer& writer)
 {
     static constexpr int fg_table[]{ 39, 30, 31, 32, 33, 34, 35, 36, 37, 90, 91, 92, 93, 94, 95, 96, 97 };
     static constexpr int bg_table[]{ 49, 40, 41, 42, 43, 44, 45, 46, 47, 100, 101, 102, 103, 104, 105, 106, 107 };
-    static constexpr int attr_table[]{ 0, 4, 7, 5, 1, 2, 3, 9 };
+    static constexpr int ul_table[]{ 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 };
+    static constexpr const char* attr_table[]{ "0", "4", "4:3", "7", "5", "1", "2", "3", "9" };
 
     auto set_color = [&](bool fg, const Color& color, bool join) {
         if (join)
@@ -255,7 +256,24 @@ void TerminalUI::Screen::set_face(const Face& face, Writer& writer)
         join = true;
     }
     if (m_active_face.bg != face.bg)
+    {
         set_color(false, face.bg, join);
+        join = true;
+    }
+    if (m_active_face.underline != face.underline)
+    {
+        if (join)
+            writer.write(";");
+        if (face.underline != Color::Default)
+        {
+            if (face.underline.isRGB())
+                format_with(writer, "58:2::{}:{}:{}", face.underline.r, face.underline.g, face.underline.b);
+            else
+                format_with(writer, "58:5:{}", ul_table[(int)(char)face.underline.color]);
+        }
+        else
+            format_with(writer, "59");
+    }
     writer.write("m");
 
     m_active_face = face;