The error comes from WithContext doesn't take into consideration that we can inject function through the Compile options with expr.Function

[antonmedv]

The error comes from WithContext doesn't take into consideration that we can inject function through the Compile options with expr.Function
with the change https://github.com/expr-lang/expr/pull/504/files we loose track of what the arguments should be with the function and the patcher can only see the function as having the arguments []any instead of the arguments we want the function to have.

Here is a test that is in the same style as TestWithContext but using expr.Function instead of applying the function to the env

func TestWithContextWithFunction(t *testing.T) {
	env := map[string]any{
		"ctx": context.TODO(),
	}

	withFunction := expr.Function("fn",
		func(params ...any) (any, error) {
			ctx := params[0].(context.Context)
			a := params[1].(int)

			return ctx.Value("value").(int) + a, nil
		},
		new(func(context.Context, int) int),
	)

	withContext := patcher.WithContext{Name: "ctx"}

	program, err := expr.Compile(
		`fn(40)`,
		expr.Env(env),
		expr.Patch(withContext),
		withFunction,
	)
	require.NoError(t, err)

	ctx := context.WithValue(context.Background(), "value", 2)
	env["ctx"] = ctx

	output, err := expr.Run(program, env)
	require.NoError(t, err)
	require.Equal(t, 42, output)
}

Originally posted by @tw1nk in #514 (reply in thread)