Remove premature lowering of return without arguments

`return` can have zero arguments - indicate this with empty children,
rather than with an invisible `K"nothing"` token.

Author: c42f

src/expr.jl

@@ -303,6 +303,8 @@ function _to_expr(node::SyntaxNode; iteration_spec=false, need_linenodes=true,
             args[1] = Expr(headsym, args[1].args...)
             headsym = :const
         end
+    elseif headsym == :return && isempty(args)
+        push!(args, nothing)
     end
     return Expr(headsym, args...)
 end

src/kinds.jl

@@ -83,7 +83,6 @@ const _kind_names =
         "CmdString"
         "true"
         "false"
-        "nothing"  # A literal `nothing`
     "END_LITERAL"
 
     "BEGIN_DELIMITERS"

src/parser.jl

@@ -1971,9 +1971,8 @@ function parse_resword(ps::ParseState)
         bump(ps, TRIVIA_FLAG)
         k = peek(ps)
         if k == K"NewlineWs" || is_closing_token(ps, k)
-            # return\nx   ==>  (return nothing)
-            # return)     ==>  (return nothing)
-            bump_invisible(ps, K"nothing")
+            # return\nx   ==>  (return)
+            # return)     ==>  (return)
         else
             # return x    ==>  (return x)
             # return x,y  ==>  (return (tuple x y))

src/syntax_tree.jl

@@ -107,8 +107,6 @@ function SyntaxNode(source::SourceFile, raw::GreenNode{SyntaxHead}, position::In
             isempty(val_range)  ?
                 Symbol(untokenize(k)) : # synthetic invisible tokens
                 Symbol(normalize_identifier(val_str))
-        elseif k == K"nothing"
-            nothing
         elseif k == K"error"
             ErrorVal()
         elseif k == K"MacroName"

test/expr.jl

@@ -302,4 +302,9 @@
         @test parse(Expr, "\n\"x\" f") ==
             Expr(:macrocall, GlobalRef(Core, Symbol("@doc")), LineNumberNode(2), "x", :f)
     end
+
+    @testset "return" begin
+        @test parse(Expr, "return x") == Expr(:return, :x)
+        @test parse(Expr, "return")  == Expr(:return, nothing)
+    end
 end

test/parser.jl

@@ -475,8 +475,8 @@ tests = [
         "struct A end"    =>  "(struct false A (block))"  => Expr(:struct, false, :A, Expr(:block))
         "struct try end"  =>  "(struct false (error (try)) (block))"
         # return
-        "return\nx"   =>  "(return nothing)"
-        "return)"     =>  "(return nothing)"
+        "return\nx"   =>  "(return)"
+        "return)"     =>  "(return)"
         "return x"    =>  "(return x)"
         "return x,y"  =>  "(return (tuple x y))"
         # break/continue