Add HierachicalHighlighter class

HierachicalHighlighter contains a map of names to HighlighterGroup
and can wrap any highlighter that wants to access user settable
sub groups.

src/highlighter_group.cc

@@ -28,14 +28,21 @@ HighlighterGroup& HighlighterGroup::get_group(StringView path, Codepoint path_se
     auto it = m_highlighters.find(id);
     if (it == m_highlighters.end())
         throw group_not_found("no such id: "_str + id);
-    HighlighterGroup* group = it->second.template target<HighlighterGroup>();
+    if (auto* group = it->second.target<HighlighterGroup>())
-    if (not group)
+    {
-        throw group_not_found("not a group: "_str + id);
         if (sep_it != path.end())
-        return group->get_group(StringView(sep_it+1, path.end()), path_separator);
+            return group->get_group({sep_it+1, path.end()}, path_separator);
-    else
         return *group;
     }
+    else if (auto* hier_group = it->second.target<HierachicalHighlighter>())
+    {
+        if (sep_it == path.end())
+            throw group_not_found("not a leaf group: "_str + id);
+        return hier_group->get_group({sep_it+1, path.end()}, path_separator);
+    }
+    else
+        throw group_not_found("not a group: "_str + id);
+}
 
 CandidateList HighlighterGroup::complete_id(StringView prefix, ByteCount cursor_pos) const
 {
@@ -50,4 +57,17 @@ CandidateList HighlighterGroup::complete_group_id(StringView prefix, ByteCount c
         });
 }
 
+HighlighterGroup& HierachicalHighlighter::get_group(StringView path, Codepoint path_separator)
+{
+    auto sep_it = std::find(path.begin(), path.end(), path_separator);
+    StringView id(path.begin(), sep_it);
+    auto it = m_groups.find(id);
+    if (it == m_groups.end())
+        throw group_not_found("no such id: "_str + id);
+    if (sep_it != path.end())
+        return it->second.get_group(StringView(sep_it+1, path.end()), path_separator);
+    else
+        return it->second;
+}
+
 }

src/highlighter_group.hh

@@ -17,7 +17,9 @@ struct group_not_found : public runtime_error
 class HighlighterGroup
 {
 public:
-    void operator()(const Context& context, HighlightFlags flags, DisplayBuffer& display_buffer);
+    void operator()(const Context& context,
+                    HighlightFlags flags,
+                    DisplayBuffer& display_buffer);
 
     void append(HighlighterAndId&& hl);
     void remove(StringView id);
@@ -31,6 +33,32 @@ private:
     id_map<HighlighterFunc> m_highlighters;
 };
 
+class HierachicalHighlighter
+{
+public:
+    using GroupMap = id_map<HighlighterGroup>;
+    using Callback = std::function<void (GroupMap& groups,
+                                         const Context& context,
+                                         HighlightFlags flags,
+                                         DisplayBuffer& display_buffer)>;
+
+    HierachicalHighlighter(Callback callback, GroupMap groups)
+        : m_callback(std::move(callback)), m_groups(std::move(groups)) {}
+
+    void operator()(const Context& context,
+                    HighlightFlags flags,
+                    DisplayBuffer& display_buffer)
+    {
+        m_callback(m_groups, context, flags, display_buffer);
+    }
+
+    HighlighterGroup& get_group(StringView path, Codepoint path_separator = 0);
+
+protected:
+    Callback m_callback;
+    GroupMap m_groups;
+};
+
 struct DefinedHighlighters : public HighlighterGroup,
                              public Singleton<DefinedHighlighters>
 {