Allow no expression in return

common/init.lua

@@ -52,7 +52,7 @@ local common = {
 	operator_priority = {
 		[";_"] = 1,
 		["$_"] = 1,
-		["@_"] = 2,
+		["@_"] = 1,
 		["_,_"] = 2,
 		["_=_"] = 3,
 		["_!_"] = 12,

parser/expression/primary/function_definition.lua

@@ -42,7 +42,6 @@ local function_parameter_maybe_parenthesis = function_parameter_no_default {
 	end
 }
 
-
 -- signature type 1: unary prefix
 -- :$-parameter exp
 -- returns symbol, parameter_tuple, rem if success
@@ -195,7 +194,7 @@ return primary {
 			-- parse expression
 			local right
 			s, right, rem = pcall(expression_to_ast, source, rem, limit_pattern, operator_priority["$_"])
-			if not s then error(("invalid expression after unop %q: %s"):format(self.operator, right), 0) end
+			if not s then error(("invalid expression in function definition: %s"):format(right), 0) end
 
 			-- return function
 			local fn = Function:new(parameters, right):set_source(source_start)

parser/expression/primary/init.lua

@@ -21,7 +21,6 @@ local primaries = {
 	-- 1
 	r("prefix.semicolon"),
 	r("prefix.function"),
-	-- 2
 	r("prefix.return"),
 	-- 3.5
 	r("prefix.else"),

parser/expression/primary/prefix/prefix_maybe_nil_right.lua

@@ -0,0 +1,21 @@
+local prefix = require("parser.expression.primary.prefix.prefix")
+local escape = require("common").escape
+local expression_to_ast = require("parser.expression.to_ast")
+
+local ast = require("ast")
+local Nil = ast.Nil
+
+return prefix {
+	parse = function(self, source, str, limit_pattern)
+		local source_start = source:clone()
+		local escaped = escape(self.operator)
+
+		local sright = source:consume(str:match("^("..escaped..")(.*)$"))
+		local s, right, rem = pcall(expression_to_ast, source, sright, limit_pattern, self.priority)
+		if not s then
+			return self:build_ast(Nil:new()):set_source(source_start), sright
+		else
+			return self:build_ast(right):set_source(source_start), rem
+		end
+	end,
+}

parser/expression/primary/prefix/return.lua

@@ -1,11 +1,11 @@
-local prefix = require("parser.expression.primary.prefix.prefix")
+local prefix_maybe_nil_right = require("parser.expression.primary.prefix.prefix_maybe_nil_right")
 
 local ast = require("ast")
 local Return = ast.Return
 
 local operator_priority = require("common").operator_priority
 
-return prefix {
+return prefix_maybe_nil_right {
 	operator = "@",
 	priority = operator_priority["@_"],