lace.builtin.define: Record the definition in error words

This wraps the defined function to record the line and word offset that
the function was defined at.

Because we abuse the define command to define subexpressions,
we also have to undo that.

2 files changed, 34 insertions, 0 deletions

diff --git a/lib/lace/builtin.lua b/lib/lace/builtin.lua
index 99d5d11..2785389 100644
--- a/lib/lace/builtin.lua
+++ b/lib/lace/builtin.lua
@@ -250,7 +250,22 @@ local function _controlfn(ctx, name)
    return cfn
 end
 
+local function wrap_call_definition_location(rule, defn)
+   local fn = defn.fn
+   function defn.fn(...)
+      local res, msg = fn(...)
+      if res == nil then
+         msg = err.offset(msg, 2)
+         msg = err.augment(msg, rule.source, rule.linenr)
+         return nil, msg
+      end
+      return res, msg
+   end
+   return defn
+end
+
 local function _do_define(exec_context, rule, name, defn)
+   defn = wrap_call_definition_location(rule, defn)
    local res, msg = engine.define(exec_context, name, defn)
    if res == nil then
       msg = err.augment(msg, rule.source, rule.linenr)
diff --git a/lib/lace/compiler.lua b/lib/lace/compiler.lua
index ec680e6..1c3aa01 100644
--- a/lib/lace/compiler.lua
+++ b/lib/lace/compiler.lua
@@ -82,6 +82,25 @@ local function transfer_args(compcontext, content, rules)
 	    msg.words = {i}
 	    return definerule, msg
 	 end
+
+         -- Fix up error location offset
+         -- The error words are offset by 2 because the "define" token and name,
+         -- but we're abusing the define command for something without those,
+         -- we are responsible for offsetting the errors back.
+         local bindname = definerule.fn
+         function definerule.fn(exec_context, rule, name, defn)
+            local fn = defn.fn
+            function defn.fn(...)
+               local res, msg = fn(...)
+               if res == nil then
+                  msg = err.offset(msg, -2)
+                  return nil, msg
+               end
+               return res, msg
+            end
+            return bindname(exec_context, rule, name, defn)
+         end
+
 	 args[#args+1] = definename
 	 rules[#rules+1] = definerule
       else