a simple hack to make caller apparent

Teliva isn't yet smart enough to know the caller of an indirect function
where the function being called goes through a local variable.

I'd expected fixing this to be a long death march. However, there's a
shockingly easy fix: just make every indirect call go through an
additional direct function call.

My policy for zet.tlv was that function 'main' could open any file. This
stopped working since I introduced spawn_main. But with this commit it's
working again.

I can also drop all my special-casing of 'main' since it's now a regular
Lua call.

We still can't rely on the caller of an indirect call. That affects
start_reading and start_writing, which really need to be part of the
framework.

src/task.lua

@@ -382,7 +382,7 @@ _M.NOP       = NOP
 
 -- Specific to Teliva
 function spawn_main()
-  task.spawn(main)
+  task.spawn(call_main)
   task.scheduler()
   assert(false, "Teliva's scheduler ran out of work; this shouldn't happen.\n"..
                 "Either a channel is blocked forever or you're reading past\n"..
@@ -391,6 +391,12 @@ function spawn_main()
   curses.getch()
 end
 
+-- This function exists only to make the call to 'main' visible to Teliva.
+-- Teliva can't yet recognize the caller of indirect calls.
+function call_main()
+  main()
+end
+
 ----------------------------------------------------------------------------
 ----------------------------------------------------------------------------
 -- Tests

src/teliva.c

@@ -322,7 +322,6 @@ void save_caller(lua_State* L, const char* name, int call_graph_depth) {
   lua_getstack(L, 1, &ar);
   lua_getinfo(L, "n", &ar);
   if (ar.name) save_caller_as(L, name, ar.name);
-  else if (call_graph_depth == 2) save_caller_as(L, name, "main");  // the way Teliva calls `main` messes with debug info
 }
 
 char* caller(lua_State* L) {
@@ -396,9 +395,6 @@ restart:
   clear();
   luaL_newmetatable(L, "__teliva_call_graph_depth");
   int cgt = lua_gettop(L);
-  // special-case: we don't instrument the call to main, but it's always at depth 1
-  lua_pushinteger(L, 1);
-  lua_setfield(L, cgt, "main");
   // segment definitions by depth
   lua_getglobal(L, "teliva_program");
   int history_array = lua_gettop(L);
@@ -514,7 +510,7 @@ restart:
   y += 2;
   mvprintw(y, 0, "functions: ");
   y++;
-  for (int depth = 1; ; ++depth) {
+  for (int depth = /*ignore call_main*/2; ; ++depth) {
     mvaddstr(y, 0, "                ");
     bool drew_anything = false;
     index_within_level = 0;