krprint: support pretty-printing functions

diff --git a/daemon/lua/krprint.lua b/daemon/lua/krprint.lua
index 5f2db3356d3c3b2d7f70c3f68782c1f65ea0afd3..11c8c76aded66d36acad5eaab23b1a993ef0e52e 100644 (file)
--- a/daemon/lua/krprint.lua
+++ b/daemon/lua/krprint.lua
@@ -13,6 +13,7 @@ function base_class.new(class, on_unrepresentable)
        local inst = {}
        inst.on_unrepresentable = on_unrepresentable
        inst.done = {}
+       inst.tab_key_path = {}
        setmetatable(inst, class.__inst_mt)
        return inst
 end
@@ -134,6 +135,9 @@ function base_class.table(self, tab)
        for idx, val in ordered_iter(tab) do
                local errors, valok, valexpr, valnote, idxok, idxexpr, idxnote
                errors = {}
+               -- push current index onto key path stack to make it available to sub-printers
+               table.insert(self.tab_key_path, idx)
+
                valok, valexpr, valnote = pcall(self.val2expr, self, val)
                if not valok then
                        table.insert(errors, string.format('value: %s', valexpr))
@@ -180,12 +184,14 @@ function base_class.table(self, tab)
                        end
                end
                table.insert(items, item)
+               table.remove(self.tab_key_path) -- pop current index from key path stack
        end  -- one key+value
        self:indent_dec()
        table.insert(items, self:indent_head() .. '}')
        return table.concat(items, self.item_sep), string.format('%s follows', tab)
 end
 
+-- machine readable variant, cannot represent all types and repeated references to a table
 local serializer_class = {
        indent_step = 0,
        item_sep = ' ',
@@ -203,6 +209,7 @@ local function static_serializer(val, on_unrepresentable)
        return string.format('%s%s', inst:format_note(note, nil, inst.item_sep), expr)
        end
 
+-- human friendly variant, not stable and not intended for machine consumption
 local pprinter_class = {
        indent_step = 4,
        item_sep = '\n',
@@ -211,6 +218,52 @@ local pprinter_class = {
        format_note = function() return '' end,
 }
 
+-- "function" is a Lua keyword so assignment below is workaround to create
+-- function pprinter_class.function(self, f)
+pprinter_class['function'] = function(self, f)
+-- thanks to AnandA777 from StackOverflow! Function funcsign is adapted version of
+-- https://stackoverflow.com/questions/51095022/inspect-function-signature-in-lua-5-1
+       assert(type(f) == 'function', "bad argument #1 to 'funcsign' (function expected)")
+       local debuginfo = debug.getinfo(f)
+       local func_args = {}
+       local args_str
+       if debuginfo.what == 'C' then  -- names N/A
+               args_str = '(?)'
+               goto add_name
+       end
+
+       pcall(function()
+               local oldhook
+               local delay = 2
+               local function hook()
+                       delay = delay - 1
+                       if delay == 0 then  -- call this only for the introspected function
+                               -- stack depth 2 is the introspected function
+                               for i = 1, debuginfo.nparams do
+                                       local k = debug.getlocal(2, i)
+                                       table.insert(func_args, k)
+                               end
+                               if debuginfo.isvararg then
+                                       table.insert(func_args, "...")
+                               end
+                               debug.sethook(oldhook)
+                               error('aborting the call to introspected function')
+                       end
+               end
+               oldhook = debug.sethook(hook, "c")  -- invoke hook() on function call
+               f(unpack({}))  -- huh?
+       end)
+       args_str = "(" .. table.concat(func_args, ", ") .. ")"
+       ::add_name::
+       local name
+       if #self.tab_key_path > 0 then
+               name = string.format('function %s', self.tab_key_path[#self.tab_key_path])
+       else
+               name = 'function '
+       end
+       return string.format('%s%s: %s', name, args_str, string.sub(tostring(f), 11))
+end
+
 -- default tostring method is better suited for human-intended output
 function pprinter_class.number(_, number)
        return tostring(number)