MBS as default shell

1 files changed, 88 insertions, 0 deletions

diff --git a/.mbs/lib/stack_trace.lua b/.mbs/lib/stack_trace.lua
new file mode 100644
index 0000000..7674813
--- /dev/null
+++ b/.mbs/lib/stack_trace.lua
@@ -0,0 +1,88 @@
+local type = type
+local debug_traceback = type(debug) == "table" and type(debug.traceback) == "function" and debug.traceback
+
+local function traceback(x)
+  -- Attempt to detect error() and error("xyz", 0).
+  -- This probably means they're erroring the program intentionally and so we
+  -- shouldn't display anything.
+  if x == nil or (type(x) == "string" and not x:find(":%d+:")) then
+    return x
+  end
+
+  if debug_traceback then
+    -- The parens are important, as they prevent a tail call occuring, meaning
+    -- the stack level is preserved. This ensures the code behaves identically
+    -- on LuaJ and PUC Lua.
+    return (debug_traceback(tostring(x), 2))
+  else
+    local level = 3
+    local out = { tostring(x), "stack traceback:" }
+    while true do
+      local _, msg = pcall(error, "", level)
+      if msg == "" then break end
+
+      out[#out + 1] = "  " .. msg
+      level = level + 1
+    end
+
+    return table.concat(out, "\n")
+  end
+end
+
+local function trim_traceback(target, marker)
+  local ttarget, tmarker = {}, {}
+  for line in target:gmatch("([^\n]*)\n?") do ttarget[#ttarget + 1] = line end
+  for line in marker:gmatch("([^\n]*)\n?") do tmarker[#tmarker + 1] = line end
+
+  -- Trim identical suffixes
+  local t_len, m_len = #ttarget, #tmarker
+  while t_len >= 3 and ttarget[t_len] == tmarker[m_len] do
+    table.remove(ttarget, t_len)
+    t_len, m_len = t_len - 1, m_len - 1
+  end
+
+  -- Trim elements from this file and xpcall invocations
+  while t_len >= 1 and ttarget[t_len]:find("^\tstack_trace%.lua:%d+:") or
+        ttarget[t_len] == "\t[C]: in function 'xpcall'" or ttarget[t_len] == "  xpcall: " do
+    table.remove(ttarget, t_len)
+    t_len = t_len - 1
+  end
+
+  return ttarget
+end
+
+--- Run a function with
+local function xpcall_with(fn)
+  -- So this is rather grim: we need to get the full traceback and current one and remove
+  -- the common prefix
+  local trace
+  local res = table.pack(xpcall(fn, traceback)) if not res[1] then trace = traceback("trace.lua:1:") end
+  local ok, err = res[1], res[2]
+
+  if not ok and err ~= nil then
+    trace = trim_traceback(err, trace)
+
+    -- Find the position where the stack traceback actually starts
+    local trace_starts
+    for i = #trace, 1, -1 do
+      if trace[i] == "stack traceback:" then trace_starts = i; break end
+    end
+
+    -- If this traceback is more than 15 elements long, keep the first 9, last 5
+    -- and put an ellipsis between the rest
+    local max = 15
+    if trace_starts and #trace - trace_starts > max then
+      local keep_starts = trace_starts + 10
+      for i = #trace - trace_starts - max, 0, -1 do table.remove(trace, keep_starts + i) end
+      table.insert(trace, keep_starts, "  ...")
+    end
+
+    return false, table.concat(trace, "\n")
+  end
+
+  return table.unpack(res, 1, res.n)
+end
+
+_ENV.traceback = traceback
+_ENV.trim_traceback = trim_traceback
+_ENV.xpcall_with = xpcall_with
\ No newline at end of file