Issues with parsing `time.String()` in Go 1.19

[Erez Rokah]

Hello!

I'm not sure if this is a bug or not. The following test will print both error messages:

```

func TestTimeStringParse(t *testing.T) {

  for i := 0; i < 100000; i++ {

    timeString := time.Now().Add(time.Duration(rand.Int63())).String()

    _, err := time.Parse(defaultStringFormat, timeString)

   if err == nil {

     t.Errorf("time.Parse(%q) should return error", timeString)

    } else {

      t.Errorf("time.Parse(%q) should not return error", timeString)

    }

  }

}

```

The failure stems from Go 1.19 adding the extra text `m=+<int>` for the monotonic clock.
This doesn't happen for every `time.String()` invocation, which is a bit confusing.
I understand one shouldn't try to parse `time.String()`, especially with the private format, however this does looks like something that worked before Go 1.19.

Would be glad to know what others think.
Cheers,
Erez

[Ian Lance Taylor]

What is defaultStringFormat?

Adding m=<int> is not new in Go 1.19.

Ian

[Erez Rokah]

The string format used is `"2006-01-02 15:04:05.999999999 -0700 MST"` which is `time.String()` internal format

[Ian Lance Taylor]

On Wed, Nov 9, 2022 at 9:00 AM Erez Rokah <er...@cloudquery.io> wrote:
>
> The string format used is `"2006-01-02 15:04:05.999999999 -0700 MST"` which is `time.String()` internal format

Thanks.

You originally asked whether this is a bug or not. I don't think this
is a bug. It's true that it's not easy to use time.Parse to parse a
string generated by time.String. That is perhaps unfortunate, but
it's a consequence of how the various functions work.

As I noted earlier the -m= has been around for a long time. I don't
know what changed in Go 1.19. When I run your test with Go 1.18, it
fails for me.

Ian

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[Erez Rokah]

Thanks for the response, I somehow thought that was added in Go 1.19. Sorry for the confusion and thanks again for the help