time: Time.Format does not provide space padding for numbers other than days

[hallazzang]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.9.2 darwin/amd64

Does this issue reproduce with the latest release?

I'm not sure I'm running the latest release of Go, but I just ran brew upgrade go on my macOS laptop and it says go 1.9.2 already installed.

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOOS="darwin"

What did you do?

I was trying to make a library that gives programmers who wanted to use Python-like strftime method on time.Time a nice Strftime function. While writing test code to test if paddings are working, I found that there is no space(literal ) padding for 'month' and 'hour' but only 'day' haves it.

To explain what happens, here's Go playground's link: https://play.golang.org/p/cAgWgVD5Tu

As you can see underscore(_) layout string doesn't work for month, hour, minute and second.

What did you expect to see?

In the above playground, I expected 9 4 for month and day.

What did you see instead?

But I've got _9 4 instead. Same for month, hour, minute and second.

I would like to patch the time package and I'd like to know whether this issue has already issued or not. Thanks.

[bradfitz]

Well, this is documented at least:

Within the format string, an underscore _ represents a space that may be replaced by a digit if the following number (a day) has two digits; for compatibility with fixed-width Unix time formats.

Up to @robpike to decide whether to extend it to support other things.

[hallazzang]

Yes, and I've found another thing that 24-hour based hour cannot represented without padding since 15(already has two digits) is proper placeholder for it. Would it be solved, too?

[robpike]

It does seem inconsistent but is it a common enough case to worry about? No one has noticed the issue before and it's easy to fix by post-processing.

What do others think?

[hallazzang]

Well I was surprised that no one has noticed this issue but me, I think the reason is that the zero padding fits well for almost every usecases. But in my opinion a consistency for standard packages matters a lot, would it be good to patch it by myself and send a pull request to this repository? I've never contributed to this large repository before, though.

[robpike]

This repository does not accept pull requests directly. Please see https://golang.org/doc/contribute.html

[hallazzang]

Thank you. I'll read it and get on my work soon!

[hallazzang]

By the way, how do you think about the 24-based hour's no-padding(7 instead of ^7 for minute, ^ represents blank space) representation? Currently it seems impossible to correctly support consistent padding rule for 24-based hour since it already has 2 digits(15). How could one workaround this?

[gopherbot]

Change https://golang.org/cl/78735 mentions this issue: time: add space padding layout strings(using underscore) for not only day but others

[rsc]

Rob will review.