Ensure stable ordering of overload candidates (#816) (#818)

Author: TristonianJones

cel/cel_test.go

@@ -1944,7 +1944,8 @@ func TestDynamicDispatch(t *testing.T) {
 		),
 	)
 	out, err := interpret(t, env, `
-		[1, 2].first() == 1
+		[].first() == 0
+		&& [1, 2].first() == 1
 		&& [1.0, 2.0].first() == 1.0
 		&& ["hello", "world"].first() == "hello"
 		&& [["hello"], ["world", "!"]].first().first() == "hello"

common/decls/decls.go

@@ -243,7 +243,8 @@ func (f *FunctionDecl) Bindings() ([]*functions.Overload, error) {
 	// performs dynamic dispatch to the proper overload based on the argument types.
 	bindings := append([]*functions.Overload{}, overloads...)
 	funcDispatch := func(args ...ref.Val) ref.Val {
-		for _, o := range f.overloads {
+		for _, oID := range f.overloadOrdinals {
+			o := f.overloads[oID]
 			// During dynamic dispatch over multiple functions, signature agreement checks
 			// are preserved in order to assist with the function resolution step.
 			switch len(args) {