hclsyntax: return cty.DynamicVal when encountering (...) and unknown

vals

hclsyntax/expression.go

@@ -260,6 +260,8 @@ func (e *FunctionCallExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnosti
 		}
 
 		switch {
+		case expandVal.Type().Equals(cty.DynamicPseudoType):
+			return cty.DynamicVal, diags
 		case expandVal.Type().IsTupleType() || expandVal.Type().IsListType() || expandVal.Type().IsSetType():
 			if expandVal.IsNull() {
 				diags = append(diags, &hcl.Diagnostic{

hclsyntax/expression_test.go

@@ -322,6 +322,21 @@ upper(
 			cty.DynamicVal,
 			1, // argument cannot be null
 		},
+		{
+			`concat(var.unknownlist...)`,
+			&hcl.EvalContext{
+				Functions: map[string]function.Function{
+					"concat": stdlib.ConcatFunc,
+				},
+				Variables: map[string]cty.Value{
+					"var": cty.ObjectVal(map[string]cty.Value{
+						"unknownlist": cty.UnknownVal(cty.DynamicPseudoType),
+					}),
+				},
+			},
+			cty.DynamicVal,
+			0,
+		},
 		{
 			`[]`,
 			nil,