Checking for existence of local file or directory

[djarnis73]

It would be nice to be able to check for existence of a file or directory as a type constraint check.

I was thinking something in the line of:

class Container {
  dir: String(isDirectory)
  file: String(exist(dir, this))
}

My use case is that I try to build a bunch of deployment config files (mix of kubernetes/drone) where some values point to files/directories where it would be nice to tell the user if file/dir could not be found.

[StefMa]

You probably can make use of read() and read?()?!
https://pkl-lang.org/main/current/language-reference/index.html#resources

exist() is kind already implemented with read(), as it throws if it doesn't exist.
Alternatively, in case you want to throw another exception or using a fallback, you can use read?() ?? throw("File does not exist")

isDirectory could maybe somehow faked with read*() 🤔

class Container {
    dir: String(read*(this).keys.length > 0)
    file: String(read?(dir + "/" + this) != null)
}

container: Container = new {
    dir = "../workflows"
    file = "x.pkl"
}

[holzensp]

I agree with @StefMa; you can already implement exists in terms of read?;

fileExists = (it) -> read?(it) != null

There is no real isDirectory or equivalent. That said, when you read a directory, the text in the resulting Resource (which doesn't have keys, btw) is the listing of the directory's contents. So, you could...

class Container {
  function fileExists(it: String) = read?(it) != null
  dir: String(fileExists(this))
  local dirListing = read(dir).text.split("\n")
  file: String(dirListing.contains(this), fileExists(dir + "/" + this))
}

^^ There's redundancy there.

[djarnis73]

Thanks for the pointers. I experimented a bit. I could not get the "directory exist" feature to work (I did not try very hard so it is probably possible), but the following typealias works nice with files:

typealias LocalFile = String((it) -> (read?("file:" + it) ?? throw("File '\(this)' does not exist")) is Any)

I can use it like:

class Container {
  dir: String = "defaultDir"
  dockerfile: String = "Dockerfile"
  fixed dockerfileWithPath: LocalFile = dir + "/" + dockerfile
}

myContainer: Container

And it will fail with:

–– Pkl Error ––
File 'defaultDir/Dockerfile' does not exist

4 | typealias LocalFile = String((it) -> (read?("file:" + it) ?? throw("File '\(this)' does not exist")) is Any)
                                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
at FileExists#LocalFile.<function#1> (file:.../FileExists.pkl, line 4)

10 | fixed fullDockerFile: LocalFile = dir + "/" + dockerfile
                                       ^^^^^^^^^^^^^^^^^^^^^^
at FileExists#Container.fullDockerFile (file:///.../FileExists.pkl, line 10)

106 | text = renderer.renderDocument(value)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
at pkl.base#Module.output.text (https://github.com/apple/pkl/blob/0.27.0/stdlib/base.pkl#L106)

If the file does not exist locally. This is good enough for my current needs.

One tiny annoyance is that the intellij plugin is clever enough to determine that the expression read?("file:" + it) ?? throw("File '\(this)' does not exist")) is Any is always true, so it highlights it as a warning, not sure if there is a way around that?