Fix JuliaLang#10502 (properly cache vararg stagedfunctions)

Previously, we only checked if the first method in the method table was staged in order to determine whether or not to newly cache a vararg type.  This patch changes the `cache_method` function to get an extra argument - `isstaged` for the specific method it is caching.

src/gf.c

@@ -479,7 +479,7 @@ static jl_value_t *ml_matches(jl_methlist_t *ml, jl_value_t *type,
 
 static jl_function_t *cache_method(jl_methtable_t *mt, jl_tuple_t *type,
  jl_function_t *method, jl_tuple_t *decl,
- jl_tuple_t *sparams)
+ jl_tuple_t *sparams, int8_t isstaged)
 {
  size_t i;
  int need_guard_entries = 0;
@@ -738,7 +738,7 @@ static jl_function_t *cache_method(jl_methtable_t *mt, jl_tuple_t *type,
  // in general, here we want to find the biggest type that's not a
  // supertype of any other method signatures. so far we are conservative
  // and the types we find should be bigger.
- if (!mt->defs->isstaged && jl_tuple_len(type) > mt->max_args &&
+ if (!isstaged && jl_tuple_len(type) > mt->max_args &&
  jl_is_vararg_type(jl_tupleref(decl,jl_tuple_len(decl)-1))) {
  size_t nspec = mt->max_args + 2;
  limited = jl_alloc_tuple(nspec);
@@ -1066,7 +1066,7 @@ static jl_function_t *jl_mt_assoc_by_type(jl_methtable_t *mt, jl_tuple_t *tt, in
  JL_GC_POP();
  if (!cache)
  return func;
- return cache_method(mt, tt, func, (jl_tuple_t*)m->sig, jl_null);
+ return cache_method(mt, tt, func, (jl_tuple_t*)m->sig, jl_null, m->isstaged);
  }
  JL_GC_POP();
  return jl_bottom_func;
@@ -1096,7 +1096,7 @@ static jl_function_t *jl_mt_assoc_by_type(jl_methtable_t *mt, jl_tuple_t *tt, in
  if (!cache)
  nf = func;
  else
- nf = cache_method(mt, tt, func, newsig, env);
+ nf = cache_method(mt, tt, func, newsig, env, m->isstaged);
  JL_GC_POP();
  return nf;
 }
@@ -1811,7 +1811,7 @@ jl_value_t *jl_gf_invoke(jl_function_t *gf, jl_tuple_t *types,
  jl_tuple_len(tpenv)/2);
  }
  }
- mfunc = cache_method(m->invokes, tt, m->func, newsig, tpenv);
+ mfunc = cache_method(m->invokes, tt, m->func, newsig, tpenv, m->isstaged);
  JL_GC_POP();
  }
 

test/staged.jl

@@ -112,3 +112,12 @@ stagedfunction f9088(x, a=5)
  :(x+a)
 end
 @test f9088(7) == 12
+
+# issue #10502
+stagedfunction f10502(x...)
+ :($x)
+end
+f10502() = ()
+@test f10502(1) == (Int,)
+@test f10502(1,2) == (Int,Int)
+@test f10502(1,2,3) == (Int,Int,Int)