Add functionality for passing previous-image flag to analyzer

[importhuman]

Description

#1198 added the previous-image flag to creator. According to #897, it needs to be added to analyzer as well.

Additional context

• This feature should be documented somewhere

[importhuman]

I'm a bit stuck on what exactly the parameter for analyzer should be. For instance, in creator in #1198, we appended -previous-image <prev-image> to the flags. As per #897, analyzer needs this in the form of analyzer <prev-image>. What is this parameter exactly that is being passed? LifecycleImage?
cc: @jromero

[aemengo]

@importhuman I'm having trouble following the question as written. In #1198, you implemented the functionality with the following line of code here:

...
   flags = append(flags, "-previous-image", l.opts.PreviousImage)
...

The analyzer would thus require the same parameter: l.opts.PreviousImage. Does this help?

[importhuman]

@aemengo yeah it does, I was initially thinking that creator already takes image as argument, so if analyzer also takes an argument, do I modify that or can I pass an extra parameter. I'll try appending the previous-image to args and make an initial PR.

[aemengo]

@importhuman Oh I understand now. Thank you for your patience with me, It's a good question.

As @natalieparellano explained to us in this slack.buildpacks.io thread: analyzer already takes an argument so:

analyzer <image>

should become

analyzer <prev-image>

And it makes sense because the analyzer phase is in fact looking for optimizations from the previous build of your application image.

[importhuman]

@aemengo so is the parameter to be changed l.opts.Image or l.opts.LifecycleImage? 😅

[aemengo]

@importhuman Ah. Well, I'm not quite so sure myself. There's an opportunity to learn here that I don't want to steal from you. 🙂

[importhuman]

@aemengo that's fair I suppose 😂 looking at tests in internal/build/lifecycle_execution_test.go, analyzer runs the phase with lifecycle image whether publish is true or false, so based on that I reckon tinkering with it is not the correct approach, rather the image should be modified. I'll work on some tests in lifecycle_execution_test.go before the next commit.