From db58b88c2d302773c44a2a7ebf8d3ea6e8b2edc7 Mon Sep 17 00:00:00 2001
From: Martin Atkins <mart@degeneration.co.uk>
Date: Mon, 15 Oct 2018 14:07:46 -0700
Subject: [PATCH] lang/funcs: short-circuit with unknown index and tuple
 collection

Since we need to know the index to know the result type for a tuple, we
need a special case here to deal with that situation and return
cty.DynamicVal; we can't predict the result type exactly until we know the
element type.
---
 lang/funcs/collection.go      |  6 ++++++
 lang/funcs/collection_test.go | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/lang/funcs/collection.go b/lang/funcs/collection.go
index e42ef0c4d..af8008c16 100644
--- a/lang/funcs/collection.go
+++ b/lang/funcs/collection.go
@@ -29,6 +29,12 @@ var ElementFunc = function.New(&function.Spec{
 		case listTy.IsListType():
 			return listTy.ElementType(), nil
 		case listTy.IsTupleType():
+			if !args[1].IsKnown() {
+				// If the index isn't known yet then we can't predict the
+				// result type since each tuple element can have its own type.
+				return cty.DynamicPseudoType, nil
+			}
+
 			etys := listTy.TupleElementTypes()
 			var index int
 			err := gocty.FromCtyValue(args[1], &index)
diff --git a/lang/funcs/collection_test.go b/lang/funcs/collection_test.go
index 7e2a49f87..42bcedf50 100644
--- a/lang/funcs/collection_test.go
+++ b/lang/funcs/collection_test.go
@@ -90,6 +90,24 @@ func TestElement(t *testing.T) {
 			cty.NumberIntVal(2),
 			cty.StringVal("hello"),
 		},
+		{
+			cty.TupleVal([]cty.Value{
+				cty.StringVal("hello"),
+				cty.StringVal("bonjour"),
+			}),
+			cty.UnknownVal(cty.Number),
+			cty.DynamicVal,
+		},
+		{
+			cty.UnknownVal(cty.Tuple([]cty.Type{cty.String, cty.Bool})),
+			cty.NumberIntVal(1),
+			cty.UnknownVal(cty.Bool),
+		},
+		{
+			cty.UnknownVal(cty.Tuple([]cty.Type{cty.String, cty.String})),
+			cty.UnknownVal(cty.Number),
+			cty.DynamicVal,
+		},
 	}
 
 	for _, test := range tests {