Pass-through single string arg for simpler and faster output

Author: jxai

README.md

@@ -62,9 +62,10 @@ log messages on stderr.
 
 #### log.tostr
 
-A custom function that takes a single value and returns its string
-representation, useful when you need richer or domain-specific output. `nil`
-by default, falling back to the plain `tostring`.
+A custom function for converting a value to its string representation, useful
+when you need richer or domain-specific output. Replaces the default behavior
+(number rounding + `tostring`). `nil` by default. A single string argument
+(the most common case) is always passed through as-is, bypassing `tostr`.
 
 An example using [inspect.lua](https://github.com/kikito/inspect.lua):
 

log.lua

@@ -42,7 +42,11 @@ end
 
 local make_msg = function(tostr, ...)
   local t = {}
-  for i = 1, select('#', ...) do
+  local argc = select('#', ...)
+  if argc == 1 and type(select(1, ...)) == "string" then
+    return select(1, ...)
+  end
+  for i = 1, argc do
     local x = select(i, ...)
     if tostr then
       t[#t + 1] = tostr(x)
@@ -68,9 +72,9 @@ local noop = function() end
 local function attach_log_methods(instance, extra_mt)
   local current_level = instance.level
   local current_name  = instance.name
+  local impls         = {}
 
   -- Build real implementations upfront, closed over `instance`.
-  local impls = {}
   for i, x in ipairs(modes) do
     local nameupper = x.name:upper()
     impls[i] = function(...)
@@ -114,12 +118,12 @@ local function attach_log_methods(instance, extra_mt)
 
   -- Remove level and name from the raw table so __newindex always fires for them.
   rawset(instance, "level", nil)
-  rawset(instance, "name",  nil)
+  rawset(instance, "name", nil)
 
   local mt = extra_mt or {}
   mt.__index = function(_, k)
     if k == "level" then return current_level end
-    if k == "name"  then return current_name  end
+    if k == "name" then return current_name end
   end
   mt.__newindex = function(t, k, v)
     if k == "level" then

test.lua

@@ -56,6 +56,11 @@ local function strip_ansi(s)
   return s:gsub("\27%[%d+m", "")
 end
 
+-- Check that a log line ends with the expected message
+local function ends_with_msg(s, msg)
+  return strip_ansi(s):sub(- #msg - 1) == msg .. "\n"
+end
+
 
 -- ── Suite: level filtering ────────────────────────────────────────────────────
 
@@ -486,7 +491,7 @@ do
 end
 
 do
-  -- custom tostr is called for each argument
+  -- custom tostr is called for each argument in multi-arg calls
   reset_log()
   log.usecolor = false
   local calls = {}
@@ -502,6 +507,40 @@ do
   assert_true("custom tostr return value appears in output", captured[1]:find("x x"))
 end
 
+do
+  -- single non-string arg goes through tostr
+  reset_log()
+  log.usecolor = false
+  local received
+  log.tostr = function(v)
+    received = v; return "<" .. tostring(v) .. ">"
+  end
+
+  capture_start()
+  log.info(42)
+  capture_stop()
+
+  assert_eq("tostr receives the non-string value", received, 42)
+  assert_true("single non-string arg formatted by tostr", ends_with_msg(captured[1], "<42>"))
+end
+
+do
+  -- single string arg bypasses tostr and equals the message exactly
+  reset_log()
+  log.usecolor = false
+  local called = false
+  log.tostr = function(v)
+    called = true; return tostring(v)
+  end
+
+  capture_start()
+  log.info("plain string")
+  capture_stop()
+
+  assert_false("tostr not called for single string arg", called)
+  assert_true("single string arg equals message exactly", ends_with_msg(captured[1], "plain string"))
+end
+
 do
   -- custom tostr bypasses number rounding
   log.tostr = function(v) return tostring(v) end
@@ -520,12 +559,12 @@ do
   local inst = log { tostr = function(v) return "T:" .. tostring(v) end, usecolor = false }
 
   capture_start()
-  inst.info("hello")
+  inst.info("hello", "world")
   capture_stop()
   assert_true("instance tostr wraps value", captured[1]:find("T:hello"))
 
   capture_start()
-  log.info("hello")
+  log.info("hello", "world")
   capture_stop()
   assert_false("global logger unaffected by instance tostr", captured[1]:find("T:hello"))
 end
@@ -538,7 +577,7 @@ do
   log.usecolor = false
 
   capture_start()
-  inst.info("hello")
+  inst.info("hello", "world")
   capture_stop()
 
   assert_true("instance inherits tostr from global logger", captured[1]:find("G:hello"))
@@ -551,7 +590,7 @@ do
   local inst = log { tostr = function(v) return "I:" .. tostring(v) end, usecolor = false }
 
   capture_start()
-  inst.info("hello")
+  inst.info("hello", "world")
   capture_stop()
   assert_true("instance tostr overrides global tostr", captured[1]:find("I:hello"))
   assert_false("global tostr not used when instance tostr set", captured[1]:find("G:hello"))