Disallow returning multiple types from modules, fixes #227

lualib/nelua/analyzer.lua

@@ -1506,7 +1506,7 @@ local function visitor_Call(context, node, argnodes, calleetype, calleesym, call
       end
       attr.calleesym = calleesym
       if calleetype then
-        attr.type = calleetype:get_return_type(1)
+        attr.type, attr.value = calleetype:get_return_type_and_value(1)
         sideeffect = calleetype.sideeffect
         if calleetype.symbol then
           calleetype.symbol:add_use_by(context.state.funcscope.funcsym)
@@ -2299,14 +2299,8 @@ function visitors.VarDecl(context, node)
       if vartype.is_nolvalue then
         varnode:raisef("variable declaration cannot be of the type '%s'", vartype)
       end
-      if vartype.is_type and not valnode then
-        varnode:raisef("a type declaration must assign to a type")
-      end
     end
     assert(symbol.type == vartype)
-    if (varnode.attr.comptime or varnode.attr.const) and not varnode.attr.nodecl and not valnode then
-      varnode:raisef("const variables must have an initial value")
-    end
     if valnode then
       context:traverse_node(valnode, {symbol=symbol, desiredtype=vartype})
       valtype = valnode.attr.type
@@ -2339,6 +2333,16 @@ function visitors.VarDecl(context, node)
       elseif vartype == primtypes.type and valtype ~= primtypes.type then
         valnode:raisef("cannot assign a type to '%s'", valtype)
       end
+    else
+      if i > 1 and (valtype and valtype.is_type) then
+        varnode:raisef("a type declaration can only assign to the first assignment expression")
+      end
+      if vartype and vartype.is_type then
+        varnode:raisef("a type declaration must assign to a type")
+      end
+      if (varnode.attr.comptime or varnode.attr.const) and not varnode.attr.nodecl then
+        varnode:raisef("const variables must have an initial value")
+      end
     end
     if not inscope then
       symbol.scope:add_symbol(symbol)
@@ -2494,14 +2498,20 @@ function visitors.Return(context, node)
         end
       end
       if retnode then
+        if rettype and rettype.is_type then
+          funcscope:add_return_value(i, retnode.attr.value)
+        end
         done = done and retnode.done and true
       end
     end
     node.done = done
   else
     context:traverse_nodes(retnodes)
     for i,retnode,rettype in iargnodes(retnodes) do
-      funcscope:add_return_type(i, rettype, retnode and retnode.attr.value, retnode)
+      funcscope:add_return_type(i, rettype, retnode)
+      if rettype and retnode and rettype.is_type then
+        funcscope:add_return_value(i, retnode.attr.value)
+      end
     end
   end
 end
@@ -2534,7 +2544,11 @@ function visitors.In(context, node)
   else
     context:traverse_node(retnode)
     local retattr = retnode.attr
-    exprscope:add_return_type(1, retattr.type, retattr.value, retnode)
+    local rettype = retattr.type
+    exprscope:add_return_type(1, retattr.type, retnode)
+    if rettype and rettype.is_type then
+      exprscope:add_return_value(1, retattr.value)
+    end
   end
 end
 

lualib/nelua/scope.lua

@@ -358,7 +358,7 @@ function Scope:resolve_symbols()
   return count
 end
 
-function Scope:add_return_type(index, type, value, refnode)
+function Scope:add_return_type(index, type, refnode)
   if not type then
     -- ignore the unknown types in recursive functions
     if refnode then
@@ -386,9 +386,19 @@ function Scope:add_return_type(index, type, value, refnode)
   elseif type and not tabler.ifind(rettypes, type) then
     rettypes[#rettypes+1] = type
   end
-  if value then
-    self.retvalues = self.retvalues or {}
-    self.retvalues[index] = value
+end
+
+function Scope:add_return_value(index, value)
+  if not value then return end
+  local retvalues = self.retvalues
+  if not retvalues then
+    retvalues = {}
+    self.retvalues = retvalues
+  end
+  if retvalues[index] == nil then
+    retvalues[index] = value
+  elseif retvalues[index] ~= value then
+    self.node:raisef("function cannot return multiple distinct compile time types")
   end
 end
 

lualib/nelua/types.lua

@@ -1785,6 +1785,21 @@ function FunctionType:get_return_type(index)
   end
 end
 
+-- Get the return value in the specified index.
+function FunctionType:get_return_type_and_value(index)
+  local rettype = self:get_return_type(index)
+  if not rettype.is_comptime then return rettype end
+  local node = self.node
+  if not node then return rettype end
+  local scope = node.scope
+  if not scope then return rettype end
+  local retvalues = scope.retvalues
+  if not retvalues then return rettype end
+  local retvalue = retvalues[index]
+  if not retvalue then return rettype end
+  return rettype, retvalue
+end
+
 -- Get the desired type when converting this type from another type.
 function FunctionType:get_convertible_from_type(type, explicit, fromcall)
   if type.is_nilptr then

spec/analyzer_spec.lua

@@ -659,7 +659,13 @@ it("function definition", function()
   ]])
   expect.analyze_ast([[
     local function f(): type return @integer end
+    local int = f()
+    local a: int = 0
   ]])
+  expect.analyze_error([[
+    local function f() return @integer, @string end
+    local int, str = f()
+  ]], "a type declaration can only assign to the first assignment expression")
   expect.analyze_error([[
     do
       global function f() end