prompt: display context if one is present

The documentation for tasksh currently says that the tasksh prompt will
display the context if there is one.  This adds the context to the
prompt.

Fixes GH issue GothenburgBitFactory#37

src/prompt.cpp

@@ -28,6 +28,8 @@
 #include <vector>
 #include <string>
 #include <Color.h>
+#include <Lexer.h>
+#include <shared.h>
 
 static std::vector <std::string> contextColors = {
   "bold white on red",
@@ -93,11 +95,22 @@ std::string promptCompose ()
   // TODO - The accumulated context, as colored tokens.
   // TODO - sync status
   // TODO - time
+  std::string prompt = "tasksh";
   auto decoration = composeContexts (true);
   if (decoration.length ())
     return "task " + decoration + "> ";
 
-  return "tasksh> ";
+  // For now, display the context (if any).
+  std::string dummy;;
+  std::string output;
+  execute ("task", {"_get", "rc.context"}, dummy, output);
+  output = Lexer::trimRight (output, "\n");
+
+  if (output != "")
+    prompt += " (" + output + ")";
+  prompt += "> ";
+
+  return prompt;
 }
 
 ////////////////////////////////////////////////////////////////////////////////