stack trace in logging toml

internal/engine.cm

@@ -324,7 +324,7 @@ var log_config = null
 var channel_sinks = {}
 var wildcard_sinks = []
 var warned_channels = {}
-var log_stack_enabled = false
+var stack_channels = {}
 
 function log(name, args) {
   var msg = args[0]
@@ -438,6 +438,7 @@ function ensure_log_dir(path) {
 function build_sink_routing() {
   channel_sinks = {}
   wildcard_sinks = []
+  stack_channels = {}
   var names = array(log_config.sink)
   arrfor(names, function(name) {
     var sink = log_config.sink[name]
@@ -445,7 +446,12 @@ function build_sink_routing() {
     if (!is_array(sink.channels)) sink.channels = []
     if (is_text(sink.exclude)) sink.exclude = [sink.exclude]
     if (!is_array(sink.exclude)) sink.exclude = []
+    if (is_text(sink.stack)) sink.stack = [sink.stack]
+    if (!is_array(sink.stack)) sink.stack = []
     if (sink.type == "file" && sink.path) ensure_log_dir(sink.path)
+    arrfor(sink.stack, function(ch) {
+      stack_channels[ch] = true
+    })
     arrfor(sink.channels, function(ch) {
       if (ch == "*") {
         wildcard_sinks[] = sink
@@ -471,13 +477,13 @@ function load_log_config() {
         terminal: {
           type: "console",
           format: "pretty",
-          channels: ["console", "error", "system"]
+          channels: ["console", "error", "system"],
+          stack: ["error"]
         }
       }
     }
   }
   build_sink_routing()
-  log_stack_enabled = log_config.stack == true
 }
 
 function pretty_format(rec) {
@@ -503,7 +509,16 @@ function pretty_format(rec) {
 function bare_format(rec) {
   var aid = text(rec.actor_id, 0, 5)
   var ev = is_text(rec.event) ? rec.event : json.encode(rec.event, false)
-  return `[${aid}] ${ev}\n`
+  var out = `[${aid}] ${ev}\n`
+  var i = 0
+  var fr = null
+  if (rec.stack && length(rec.stack) > 0) {
+    for (i = 0; i < length(rec.stack); i = i + 1) {
+      fr = rec.stack[i]
+      out = out + `    at ${fr.fn} (${fr.file}:${text(fr.line)}:${text(fr.col)})\n`
+    }
+  }
+  return out
 }
 
 function sink_excluded(sink, channel) {
@@ -549,7 +564,7 @@ log = function(name, args) {
   }
 
   caller = caller_info(2)
-  if (log_stack_enabled) stack = os.stack(1)
+  if (stack_channels[name]) stack = os.stack(1)
   rec = {
     actor_id: _cell.id,
     timestamp: time.number(),