Proposal for the addition of fs/touch

[jdjohnston]

The idea is to provide a basic touch function in the babashka.fs namespace. The
function would provide an easy way to create files (e.g., for testing) or an easy way to ensure a file has a certain timestamp (can be useful in a build process), perhaps to "dirty" the file without actually changing it. Google for something like "linux use cases for touch(1)" for more ideas.

The intent is not to "clone" touch(1). As part of a Babashka library it can be used in ways that would be difficult to duplicate with touch(1) in the shell. OTOH, for some of the more esoteric options that won't be implemented, one can always invoke a subprocess if needed.

fs/touch
[fil] [fil tim]

• If fil doesn't exist, create it
• If not specified, tim defaults to the time the function is called
  • If tim is specified it should be suitable for fs/set-last-modified-time
• Set the file last-modified time for fil to tim

(It might seem inelegant to set a freshly created file to the current time, but I suspect that's the most direct code path & not a efficency concern for typical use.)

If fil refers to a symbolic link, the default behavior is to follow the link and set the
time of the target. This matches the default for Gnu touch(1). To specify other
behavior, pass an option map {:nofollow-links true}, matching the behavior of most fs functions. (At least once #231 is taken care of)

[lread]

This seems like a good idea to me.

In #231 I did discover that JDK 11 for both macOS and Linux and JDK 21 for Linux will throw when attempting to set last modified time on a link. But we can just add touch to the section where I talked about that in the README.

If you like this idea @borkdude, I am happy to do up a PR with appropriate tests.

[borkdude]

ok!

[lread]

I'm thinking about the fn arglists.

Instead of proposed [path],[path time], maybe instead [path], [path opts].
Where recognized opts are :nofollow-links and :time.

The advantage of moving time to an option is that if I want to use :nofollow-links without specifying a time, I don't have this awkwardness:

(touch "some-file" nil {:nofollow-links true})

We instead just have:
(touch "some-file" {:nofollow-links true})

[jdjohnston]

@lread Or, check to see if the 2nd argument is a map. I suspect choosing a timestamp will be more wanted than not following a symlink, especially as it's not even possible to touch symlinks on some systems.

BTW, not being allowed to modify a symlink may be more of a system design & not a JVM bug. Gnu touch(1) has a --no-dereference option, but notes that it's only useful on systems that can change the timestamp of a symlink.

[lread]

Thanks @jdjohnston, we'll let @borkdude decide.

touch arglists

Option 1: [path], [path time], [path time opts]

Cons:

• requires specification of time if only interested in opts: (touch "file" nil {:nofollow-links true})

Option 2: [path], [path time-or-opts], [path time opts]

Pros:

• could be considered more natural for common usage case (touch "file" my-time-here)

Cons:

• a bit more complicated to implement and describe

Option 3: [path], [path opts]

Pros:

• simple

Cons:

• common use case might be considered a little more awkward? (touch "file" {:time my-time-here})

Proposal

I think I still like option 3, but will go with whatever you like.

[lread]

@jdjohnston, re:

BTW, not being allowed to modify a symlink may be more of a system design & not a JVM bug. Gnu touch(1) has a --no-dereference option, but notes that it's only useful on systems that can change the timestamp of a symlink.

Thanks, I noticed this too, but if you look at my check:

fs/test/babashka/fs_test.clj

Lines 26 to 29 in 686de26

	(def cant-set-last-modified-time-on-sym-link?
	"Some os jdk combos have bugs in that they do not allow setting last modfieid time on a symbolic link"
	(or (and (= :unix (util/os)) (= 11 (util/jdk-major)))
	(and (= :mac (util/os)) (#{11 21} (util/jdk-major)))))

You'll notice that, for at least the OSes and file systems we test on, seems like JDK bugs.

[borkdude]

Definitely [path opts].