# HG changeset patch
# User Matthew Wild <mwild1@gmail.com>
# Date 1546174558 0
# Node ID 848fd204708ccc3dd840ab253148ee3fb94129df
# Parent  0dbb285f903edca5e8db751578b4fecfb1808933
util.error: Add new util library for structured errors

diff -r 0dbb285f903e -r 848fd204708c util/error.lua
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/util/error.lua	Sun Dec 30 12:55:58 2018 +0000
@@ -0,0 +1,40 @@
+local error_mt = { __name = "error" };
+
+function error_mt:__tostring()
+	return ("error<%s:%s:%s>"):format(self.type, self.condition, self.text);
+end
+
+local function is_err(e)
+	return getmetatable(e) == error_mt;
+end
+
+local function new(e, context, registry)
+	local template = (registry and registry[e]) or e or {};
+	return setmetatable({
+		type = template.type or "cancel";
+		condition = template.condition or "undefined-condition";
+		text = template.text;
+
+		context = context or template.context or { _error_id = e };
+	}, error_mt);
+end
+
+local function coerce(ok, err, ...)
+	if ok or is_err(err) then
+		return ok, err, ...;
+	end
+
+	local new_err = setmetatable({
+		native = err;
+
+		type = "cancel";
+		condition = "undefined-condition";
+	}, error_mt);
+	return ok, new_err, ...;
+end
+
+return {
+	new = new;
+	coerce = coerce;
+	is_err = is_err;
+}