Fix array with external size

sszgen/generator/generator.go

@@ -1043,6 +1043,18 @@ func (e *env) parseASTFieldType(name, tags string, expr ast.Expr) (*Value, error
 					return nil, fmt.Errorf("alias ref not found: %s", obj.Name)
 				}
 				astSize = &num
+			case *ast.SelectorExpr:
+				// TODO: this does not take into account the package name.
+				// If there are two exported const with the same name it is going to collide.
+				sel := obj.Sel.Name
+
+				num, ok := e.resolveAlias(sel)
+				if !ok {
+					return nil, fmt.Errorf("alias ref not found: %s", sel)
+				}
+				astSize = &num
+			default:
+				return nil, fmt.Errorf("unsupported array length type %T", obj)
 			}
 		}
 		if astSize != nil {

sszgen/testcases/issue_164.go

@@ -0,0 +1,10 @@
+package testcases
+
+import "github.com/ferranbt/fastssz/sszgen/testcases/other2"
+
+//go:generate go run ../main.go --path issue_164.go --include ./other2
+
+type Issue64 struct {
+	// Encoding generated will be for slice and not array
+	FeeRecipientAddress [other2.Size]byte
+}

sszgen/testcases/other2/case4.go

@@ -1,3 +1,5 @@
 package other2
 
 type Case4Slot uint64
+
+const Size = 120