Improve error messages for static errors on polymorphic functions

nelua/analyzer.lua

@@ -1056,7 +1056,7 @@ local function visitor_Call(context, node, argnodes, calleetype, calleesym, call
         calleetype = nil
         calleesym = nil
         if knownallargs then
-          local polyeval = polycalleetype:eval_poly(polyargs)
+          local polyeval = polycalleetype:eval_poly(polyargs, node)
           if polyeval and polyeval.node and polyeval.node.attr.type then
             calleesym = polyeval.node.attr
             calleetype = polyeval.node.attr.type
@@ -2232,7 +2232,13 @@ function visitors.FuncDef(context, node, polysymbol)
           end
         end
       end
+      -- pop node and then push again to fix error message traceback
+      context:pop_node()
+      -- used to generate error messages
+      context:push_state().polysrcnode = polyeval.srcnode
       context:traverse_node(polynode, symbol)
+      context:pop_state()
+      context:push_node(node)
       assert(traits.is_symbol(polynode.attr))
     end
   end

nelua/analyzercontext.lua

@@ -123,6 +123,10 @@ end
 function AnalyzerContext:traceback()
   local nodes = self.visiting_nodes
   local ss = sstream()
+  local polysrcnode = self.state.polysrcnode
+  if polysrcnode then
+    ss:add(polysrcnode:format_message('from', 'polymorphic function instantiation'))
+  end
   for i=1,#nodes-1 do
     local node = nodes[i]
     if node._astnode and node.tag ~= 'Block' then

nelua/types.lua

@@ -1651,10 +1651,10 @@ function PolyFunctionType:get_poly_eval(args)
   end
 end
 
-function PolyFunctionType:eval_poly(args)
+function PolyFunctionType:eval_poly(args, srcnode)
   local polyeval = self:get_poly_eval(args)
   if not polyeval then
-    polyeval = { args = args }
+    polyeval = { args = args, srcnode = srcnode}
     table.insert(self.evals, polyeval)
   end
   return polyeval
@@ -2115,7 +2115,8 @@ end
 
 -- Checks if an attr can match a concept.
 function ConceptType:get_convertible_from_attr(attr, _, argattrs)
-  local type, err = self.func(attr, argattrs)
+  local concept_eval_func = self.func -- alias to have better error messages
+  local type, err = concept_eval_func(attr, argattrs)
   if type == true then -- concept returned true, use the incoming type
     assert(attr.type)
     type = attr.type
@@ -2222,7 +2223,8 @@ end
 
 -- Evaluate a generic to a type by calling it's function defined in the preprocessor.
 function GenericType:eval_type(params)
-  local ok, ret = except.trycall(self.func, table.unpack(params))
+  local generic_eval_func = self.func -- alias to have better error messages
+  local ok, ret = except.trycall(generic_eval_func, table.unpack(params))
   if not ok then
     -- the generic creation failed due to a lua error in preprocessor function
     return nil, ret

nelua/utils/errorer.lua

@@ -44,10 +44,10 @@ local function get_pretty_source_pos_errmsg(src, lineno, colno, errmsg, errname,
   local errtraceback = ''
 
   -- extract traceback from message, to move it to the end of the message
-  local tracebackpos = errmsg:find('stack traceback:', 1, true)
+  local tracebackpos = errmsg:find('%s*stack traceback%:')
   if tracebackpos then
-    errtraceback = '\n' .. errmsg:sub(tracebackpos)
-    errmsg = errmsg:sub(1, tracebackpos)
+    errtraceback = errmsg:sub(tracebackpos)
+    errmsg = errmsg:sub(1, tracebackpos-1)
   end
 
   -- choose the color for the message

nelua/visitorcontext.lua

@@ -74,6 +74,16 @@ function VisitorContext:set_visitors(visitors)
   self.default_visitor = visitors.default_visitor or traverser_default_visitor
 end
 
+function VisitorContext:push_node(node)
+  local nodes = self.visiting_nodes
+  nodes[#nodes + 1] = node
+end
+
+function VisitorContext:pop_node()
+  local nodes = self.visiting_nodes
+  nodes[#nodes] = nil
+end
+
 function VisitorContext:get_parent_node()
   local nodes = self.visiting_nodes
   return nodes[#nodes - 1]

spec/08-runner_spec.lua

@@ -164,4 +164,13 @@ mylib - terminate]])
   os.remove('mylib_test')
 end)
 
+it("error tracebacks", function()
+  assert.run_error({'--eval',[[
+    local function f(x: auto)
+      ## static_error('fail')
+    end
+    f(1)
+  ]]}, "polymorphic function instantiation")
+end)
+
 end)