Special-case Vararg handling when contained in an NTuple.

Author: maleadt

src/jltypes.c

@@ -2248,7 +2248,26 @@ static jl_value_t *inst_tuple_w_(jl_value_t *t, jl_typeenv_t *env, jl_typestack_
     int i;
     for (i = 0; i < ntp; i++) {
         jl_value_t *elt = jl_svecref(tp, i);
-        jl_value_t *pi = inst_type_w_(elt, env, stack, check);
+        jl_value_t *pi = NULL;
+        if (jl_is_vararg(elt)) {
+            // special-case Vararg when contained in Tuple: normally we disallow non-type T,
+            // but NTuple{2,N} should work for StaticArrays.jl (see JuliaLang/julia#51244).
+            jl_vararg_t *va = (jl_vararg_t*)elt;
+            jl_value_t *T = NULL;
+            if (va->T) {
+                T = inst_type_w_(va->T, env, stack, check);
+                if (!jl_is_type(T) && !jl_is_typevar(T)) {
+                    // temporarily swap out Vararg{T} for Vararg{Any}
+                    va->T = (jl_value_t*) jl_any_type;
+                } else
+                    T = NULL;
+            }
+            pi = inst_type_w_(elt, env, stack, check);
+            if (T)
+                ((jl_vararg_t*)pi)->T = T;
+        } else {
+            pi = inst_type_w_(elt, env, stack, check);
+        }
         iparams[i] = pi;
         if (ip_heap)
             jl_gc_wb(ip_heap, pi);

test/core.jl

@@ -8097,3 +8097,13 @@ end
 let lin = Core.LineInfoNode(Base, first(methods(convert)), :foo, Int32(5), Int32(0))
     @test convert(LineNumberNode, lin) == LineNumberNode(5, :foo)
 end
+
+# JuliaLang/julia#51228: bad Varargs should be disallowed
+let
+    @test_throws TypeError Vararg{2,2}
+    # ... but should still be allowed inside of a Tuple
+    @test_broken Tuple{Vararg{2,2}} === Tuple{2,2}
+    # ... because it's used for the NTuple definition
+    @test NTuple{2,2} === Tuple{2,2}
+    # ... which is used by e.g. StaticArrays.jl
+end