Disable check for missing predicate during parseing

As we may not have env/fn override for disabled builtin just yet. For example, during expr.Run, or compile without expr.Env.

Author: antonmedv

test/issues/924/issue_test.go

@@ -0,0 +1,23 @@
+package issue_test
+
+import (
+	"testing"
+
+	"github.com/expr-lang/expr"
+	"github.com/expr-lang/expr/internal/testify/require"
+)
+
+func TestIssue924_allow_disabling_builtins_and_providing_fn_at_runtime(t *testing.T) {
+	// We disable the builtin "upper", but do not env information,
+	// but we can provide a function at runtime.
+	program, err := expr.Compile(`upper(1)`, expr.DisableBuiltin("upper"))
+	require.NoError(t, err)
+
+	env := map[string]any{
+		"upper": func(a int) int { return a },
+	}
+
+	out, err := expr.Run(program, env)
+	require.NoError(t, err)
+	require.Equal(t, 1, out)
+}