Test: use infer_return_type for @inferred instead of return_types (#54752)

The implementation can be slightly more simply.

Author: aviatesk

stdlib/Test/src/Test.jl

@@ -1900,7 +1900,7 @@ function get_testset_depth()
     return length(testsets)
 end
 
-_args_and_call(args...; kwargs...) = (args[1:end-1], kwargs, args[end](args[1:end-1]...; kwargs...))
+_args_and_call((args..., f)...; kwargs...) = (args, kwargs, f(args...; kwargs...))
 _materialize_broadcasted(f, args...) = Broadcast.materialize(Broadcast.broadcasted(f, args...))
 
 """
@@ -1982,25 +1982,24 @@ function _inferred(ex, mod, allow = :(Union{}))
         quote
             let allow = $(esc(allow))
                 allow isa Type || throw(ArgumentError("@inferred requires a type as second argument"))
-                $(if any(a->(Meta.isexpr(a, :kw) || Meta.isexpr(a, :parameters)), ex.args)
+                $(if any(@nospecialize(a)->(Meta.isexpr(a, :kw) || Meta.isexpr(a, :parameters)), ex.args)
                     # Has keywords
                     args = gensym()
                     kwargs = gensym()
                     quote
                         $(esc(args)), $(esc(kwargs)), result = $(esc(Expr(:call, _args_and_call, ex.args[2:end]..., ex.args[1])))
-                        inftypes = $(gen_call_with_extracted_types(mod, Base.return_types, :($(ex.args[1])($(args)...; $(kwargs)...))))
+                        inftype = $(gen_call_with_extracted_types(mod, Base.infer_return_type, :($(ex.args[1])($(args)...; $(kwargs)...))))
                     end
                 else
                     # No keywords
                     quote
                         args = ($([esc(ex.args[i]) for i = 2:length(ex.args)]...),)
                         result = $(esc(ex.args[1]))(args...)
-                        inftypes = Base.return_types($(esc(ex.args[1])), Base.typesof(args...))
+                        inftype = Base.infer_return_type($(esc(ex.args[1])), Base.typesof(args...))
                     end
                 end)
-                @assert length(inftypes) == 1
                 rettype = result isa Type ? Type{result} : typeof(result)
-                rettype <: allow || rettype == typesplit(inftypes[1], allow) || error("return type $rettype does not match inferred return type $(inftypes[1])")
+                rettype <: allow || rettype == typesplit(inftype, allow) || error("return type $rettype does not match inferred return type $inftype")
                 result
             end
         end