Improvements in 'testes/cstack.lua'

- tests show progress in real time, so that we can see maximum
stack levels even if test crashes.
- new test for recursion continuing into message handler.

testes/cstack.lua

@@ -13,20 +13,40 @@ local function checkerror (msg, f, ...)
   assert(not s and string.find(err, msg))
 end
 
+local count
+local back = string.rep("\b", 8)
+local function progress ()
+  count = count + 1
+  local n = string.format("%-8d", count)
+  io.stderr:write(back, n)
+end
 
-do    -- simple recursion
-  local count = 0
+
+do    print("testing simple recursion:")
+  count = 0
   local function foo ()
-    count = count + 1
+    progress()
     foo()
   end
   checkerror("stack overflow", foo)
-  print("  maximum recursion: " .. count)
+  print("\tfinal count: ", count)
+end
+
+
+do  print("testing stack overflow in message handling")
+  count = 0
+  local function loop (x, y, z)
+    progress()
+    return 1 + loop(x, y, z)
+  end
+  local res, msg = xpcall(loop, loop)
+  assert(msg == "error in error handling")
+  print("\tfinal count: ", count)
 end
 
 
 -- bug since 2.5 (C-stack overflow in recursion inside pattern matching)
-do
+do  print("testing recursion inside pattern matching")
   local function f (size)
     local s = string.rep("a", size)
     local p = string.rep(".?", size)
@@ -38,25 +58,25 @@ do
 end
 
 
--- testing stack-overflow in recursive 'gsub'
-do
-  local count = 0
+do  print("testing stack-overflow in recursive 'gsub'")
+  count = 0
   local function foo ()
-    count = count + 1
+    progress()
     string.gsub("a", ".", foo)
   end
   checkerror("stack overflow", foo)
-  print("  maximum 'gsub' nest (calls): " .. count)
+  print("\tfinal count: ", count)
 
-  -- can be done with metamethods, too
+  print("testing stack-overflow in recursive 'gsub' with metatables")
   count = 0
   local t = setmetatable({}, {__index = foo})
   foo = function ()
     count = count + 1
+    progress(count)
     string.gsub("a", ".", t)
   end
   checkerror("stack overflow", foo)
-  print("  maximum 'gsub' nest (metamethods): " .. count)
+  print("\tfinal count: ", count)
 end
 
 print'OK'