Add simple markup support to generate display lines from strings

The syntax is simply {face} to enable the given face, use \{ to
escape a {, and \\ to escape a \.

src/commands.cc

@@ -891,6 +891,7 @@ const CommandDesc echo_cmd = {
     "echo <params>...: display given parameters in the status line",
     ParameterDesc{
         { { "color", { true,  "set message color" } },
+          { "markup", { false, "parse markup" } },
           { "debug", { false, "write to debug buffer instead of status line" } } },
         ParameterDesc::Flags::SwitchesOnlyAtStart
     },
@@ -902,6 +903,8 @@ const CommandDesc echo_cmd = {
         String message = join(parser, ' ', false);
         if (parser.get_switch("debug"))
             write_to_debug_buffer(message);
+        else if (parser.get_switch("markup"))
+            context.print_status(parse_display_line(message, get_face("StatusLine")));
         else
         {
             auto face = get_face(parser.get_switch("color").value_or("StatusLine").str());

src/display_buffer.cc

@@ -4,6 +4,8 @@
 #include "buffer.hh"
 #include "utf8.hh"
 
+#include "face_registry.hh"
+
 namespace Kakoune
 {
 
@@ -250,4 +252,55 @@ void DisplayBuffer::optimize()
     for (auto& line : m_lines)
         line.optimize();
 }
+
+DisplayLine parse_display_line(StringView line, Face default_face)
+{
+    DisplayLine res;
+    bool was_antislash = false;
+    auto pos = line.begin();
+    String content;
+    Face face = default_face;
+    for (auto it = line.begin(), end = line.end(); it != end; ++it)
+    {
+        const char c = *it;
+        if (c == '{')
+        {
+            if (was_antislash)
+            {
+                content += StringView{pos, it};
+                content.back() = '{';
+                pos = it + 1;
+            }
+            else
+            {
+                content += StringView{pos, it};
+                res.push_back({std::move(content), face});
+                content.clear();
+                auto closing = std::find(it+1, end, '}');
+                if (closing == end)
+                    throw runtime_error("unclosed face definition");
+                face = merge_faces(default_face, get_face({it+1, closing}));
+                it = closing;
+                pos = closing + 1;
+            }
+            was_antislash = false;
+        }
+        if (c == '\\')
+        {
+            if (was_antislash)
+            {
+                content += StringView{pos, it};
+                pos = it + 1;
+                was_antislash = false;
+            }
+            else
+                was_antislash = true;
+        }
+    }
+    content += StringView{pos, line.end()};
+    if (not content.empty())
+        res.push_back({std::move(content), face});
+    return res;
+}
+
 }

src/display_buffer.hh

@@ -140,6 +140,8 @@ private:
     AtomList  m_atoms;
 };
 
+DisplayLine parse_display_line(StringView line, Face default_face);
+
 class DisplayBuffer : public UseMemoryDomain<MemoryDomain::Display>
 {
 public:

src/string.hh

@@ -118,6 +118,8 @@ public:
     [[gnu::always_inline]]
     void append(const char* data, ByteCount count) { m_data.append(data, (size_t)(int)count); }
 
+    void clear() { m_data.clear(); }
+
     void push_back(char c) { m_data.push_back(c); }
     void resize(ByteCount size) { m_data.resize((size_t)(int)size); }
     void reserve(ByteCount size) { m_data.reserve((size_t)(int)size); }