chapter-07.srt

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Chapter 07.
Specifying dependencies.

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JC: OK so we just committed the working target class.

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It can't do an awful lot just
yet, it can just run the commands.

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So if we go back to...

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What did we have in here. My test file.

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When I was sketching this out earlier,
down here I told each of the targets to build.

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They're all just isolated.

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A better user interface would be to do that.

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And have everything needed to
produce the final result just happen.

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For that sort of thing you're going to need to
know for example, that bundle.js will depend on...

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hello_js and complimenter_js

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Whereas these won't depend on anything.

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They are their own things.

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Although they do arguably depend on their source code.

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In order for the build system to be lazy
and work out if any more work needs doing,

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it will need to know about that relationship.

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So it's probably advisable if we say...

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Here we have these target
objects to represent these things.

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but for these source files,
we could say that they are...

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For example, hello_coffee is a
Target.new('example/src/hello.coffee',

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which actually depends on nothing because the
source code you wrote is not derived from anything.

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And it has no build instructions because
you wrote it so it doesn't need generating.

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And then this could take that as a dependency.

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And you can do the same for
complimenter, and what have you.

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I'm on the fence about whether to pass
these things around as values or by name.

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Because, to pass this by saying
`example/src/hello.coffee`...

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TS: What's the trade off there?
Why would you want to do it one way or the other?

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JC: Good question, if you do them by
name you can write your target in any order.

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This can be beneficial. This is
supposed to be a declarative system.

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It can also mean that you make
dependencies on things that don't exist yet.

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So for example complimentor.js
won't exist when you start the build.

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The target represents something that will exist
in the future so you don't need the file to exist.

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But having the pass by name means that you
can do something for example, by having patterns.

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Like if you want to say *.js depends on *.coffee,

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we don't want to have to write all these
targets out by hand once the project gets large.

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So you may want to have some general
rule for how you get from one to the other.

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TS: It sounds like that may
be more complicated though.

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JC: Yeah, erh... We can
probably start by passing by value

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and if it becomes a problem we can pass by name,

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and then have those names be looked up
in something else but turned into the values.

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That should be a fairly minor change to make later.

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So let's do the pass by value thing.

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So if we go back to our spec.

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I already had this open
because it was in another shell.

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Yes, so... This is all talking
about running instructions.

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We also want to talk about having dependencies.

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So we've decided that the target is going to
have a new argument, which is its dependencies.

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[Silence]

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That ought to run but it doesn't... Why not?

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[James is thinking]

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Oh yes, OK so in the tests we need...

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I need to write that properly...
Dependencies is some list.

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And I like things that line up.

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So that ought to be fine.

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So these tests are now testing
a thing that has no dependencies.

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Ultimately we would like to have
a target that will depend on something else,

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and if you build your target it
will also build the other thing.

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Maybe this is where we get
into an integration test scenario.

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Because I'm going to have two target objects
maybe writing unit tests against those is...

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I could write a test to say when you call
build on this call build on this other thing,

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but maybe that's specifying
the implementation too much.

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So I'm going to try and write...

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spec/features is where I'm
going to put my integration test.

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dependent_targets_spec.rb

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[Silence]

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No that's not how you write specs is it?

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describe 'dependent targets' do

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[James thinks]

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Say when one target depends on another.

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As something simple, I'm going to say that if you have...

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what's something simple we can
do with files, just like cat-ing them.

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So if you have file c that is...

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I'll write it in code, that might be a bit clearer.

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So if we say...

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Not quite sure how to phrase this yet but...

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let's say that we have...

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There exists a file called a.txt that
just contains an A with a new line in it.

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And likewise there are some files called
b and c that have their letters in them.

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[Silence]

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So if there are those files,
then you have your first target.

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And let's put these somewhere... Like in spec/tmp.

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[Silence]

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So if the first target is spec/tmp/one.txt.

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And that's new with that.

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And it has no dependencies, or rather
it does have dependencies which are...

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Sorry I got a bit side tracked.

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So file_a.

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TS: So we need targets to represent these files
even though there not going to be built in any way.

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There will be some nicer user
interface around this at some point.

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But it makes this a bit more
complicated to pass in those values,

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because you have to make values
for things that are just primitive files.

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TS: Whereas if you identified things by name,

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the assumption would have been if I've named
something by name it isn't a target it's just a file.

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JC: Yes.

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So these have no dependencies in them,
no build instructions, so they can be done like that.

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That's b that's c.

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So if this depends on file_a and file_b,

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And works by cat-ing spec/temp/a.txt
spec/temp/b.txt into spec/temp/one.txt.

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And the second target is called second.

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And that works by depending
on first_target and file_c.

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Then that is going to work by taking one.txt
and c.txt and putting that into the second.

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I suppose this could be our before block.

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[Silence]

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TS: So you haven't actually built anything yet?

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JC: No.

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If we just build the second target then we expect
File.read(spec/tmp/second.txt) to equal...

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A newline, B newline, C newline.

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Because everything has
been concatenated together.

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[Silence]

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I'm going to  make some helper functions here.

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So I've made this file helper
here, I just need to define that.

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I've made this helper because I want everything
to be cleaned up automatically afterwards.

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This helper is going to make the file
with that content and keep track of it.

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And then use an `after` hook to remove all of them.

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TS: OK.

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JC: So file utils has a `mkdir_p` function.

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We can make that, and then we can `File.open`,
the path name and write content into that.

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[Silence]

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Then we can store the path name in there.

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[Silence]

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And then as an `after` hook, we can say...

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spec_files.each do path name.

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Is it `File.unlink` to delete things?

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So then we ought not to be left
with loads of files that exist between tests.

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and cause subsequent tests
to not do the right thing.

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So does this say what we actually want?

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We have 3 files and they have content.

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And we've made targets for them and
the first target depends on a and b

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and if you cat those two
files together you get one.txt.

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The second target depends on
the first target and file c

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and if you can cat those two
to make the second file, that works.

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The way things are at the moment,
if we just run second_target.build,

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it might end up throwing because
this one.txt file won't exist.

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So cat in that situation, I can't remember...
If it fails silently and returns zero or not.

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We'll find out, but either way.. It should throw
or it shouldn't have the right content in it.

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A and B will be missing.

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So let's have a go at running those spec features.

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No variable `second_target` on where... 38.

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Ah yes.

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[Silence]

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That's a local variable that split apart.

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Just run that.

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We've got a failed command from line
38 where we tried to build that thing.

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I assume because cat is failing.

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It would be nice if that error told us what
command had failed. That would be really helpful.

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So let's make it do that, so
we know, lib/fakemake/target.

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Raise fake command.

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Unless system(instruction)
message equals "command failed" with the instruction.

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TS: Right.

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[Silence]

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JC: Raise that.

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[Silence]

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Command failed: cat spec/tmp/one. So that is expected.

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I hope those files are not hanging around in tmp.

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So this knows how to clean up the files we created
with `file` but it doesn't know how to clean up.

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TS: How you going to fix that?

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JC: We could poke those things into
the array so it knows about them,

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but it still feels a little unclean.

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I accidentally made a new shell there.

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We could just nuke the tmp directory.

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I think that's maybe why I put them in a directory in
the first place, so you can just wipe the slate clean.

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So let's do that and then we
don't need this tracking stuff.

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I have put this `spec/tmp` all over the test,
maybe that's something I should clean up.

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I maybe wanted to say...

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What I originally wanted to do was say file
a.text and then have that created spec/tmp.

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But to make these commands work I would
have had to change process directory into there.

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Which we could do, I think I'm happier with that.

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Lets remove those.

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[Silence]

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Because they're really just
crufting everything up.

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If we do that... `in_tmp_dir`.

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[Silence]

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FileUtils has another nice helper function
where you can FileUtils.cd to somewhere.

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[Silence]

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Just pass the block through, (it takes a block).

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It changes working directory
into somewhere, runs the block,

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and then comes back out again to
wherever you were before, which is kind of nice.

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TS: So you're not having to do
any clean up of the current stuff,

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it just goes back to what it was when you started.

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JC: Exactly.

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So creating those files...

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We don't do anything, these just make target objects,
they don't run system calls or write any files.

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So file would have to make that temp directory.

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And then put that in here.

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So if we make those files inside spec/tmp
and then run everything in that directory,

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and afterwards remove it again,
everything should be OK, I think.

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Let's see what it makes of that.

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"Wrong number of arguments (0 for 1) on line 10"

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Oh I didn't actually pass an argument
to that one when I used it did I?

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It's just to to hide where
we're storing things from the code.

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Command failed cat one with c didn't work

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And that temp directory has gone away, so that's nice.

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OK, I feel better about that.
TS: OK good.