Add ability to define templateAttributes within a target

[tomquist]

This allows parameterizing templates. One specific problem I wanted to solve with this issue is that I have a multi-framework project where framework-targets are specified by a target template. Each framework consists of the framework itself and a corresponding test target. The framework template is specified like this:

targetTemplates:
  Module:
    platform: iOS
    type: framework
    sources: [modules/$target_name/Sources]

Now I'd like to create a template for the test target where the test-files are placed in modules/<ModuleName>/Tests. I have no way of defining a common template for this.

When this PR is merged, I'm able to define the following template:

targetTemplates:
  ModuleTests:
    platform: iOS
    type: bundle.unit-test
    sources: [modules/$targetUnderTest/Tests]
    dependencies:
      target: $targetUnderTest

and use it like this:

targets:
  MyFramework:
    templates: [Module]
  MyFrameworkTests:
    templates: [ModuleTests]
    templateAttributes:
      targetUnderTest: MyFramework

[AlexisQapa]

What about going even further and define associated templates for tests into the tested target template ? This would give us the ability to define only targets of interest.

targetTemplates:
Module:
platform: iOS
type: app
sources: [modules/sources]
tests:
template: ModuleTest

use
targets:
MyFramework:
templates: [Module]

I don't know if people use more than a unit (and for app a ui) test targets

[tomquist]

I think my solution solves the issue in a more general way and would also be useful for many other use cases. I agree that it would also be a good idea to have some way to automatically generate an associated test target for a framework target but this can still be done separately.

[AlexisQapa]

That's what I thoughts I'll give this a try when I can and give you feedbacks

[yonaskolb]

Awesome, thank you @tomquist, this is fantastic addition!

I wonder if now that the replacement strings can be anything if the syntax should be a bit more verbose so as not to cause any clashes. For example ${framework_name} instead of $framework_name.
Before we could get away with just the $ as the names of the replacements were known and deemed "safe", now I'm not so sure. If we did use a newer syntax, it might be worth updating to ${target_name} and ${platform} as well, while keeping backwards compatibility. What do you think?

[tomquist]

Regarding your suggestion to use ${attributeName} instead of $attributeName: I totally agree but didn't want to make the change without discussing first. I'll try to implement that. Ideally xcodegen would show a warning when $target_name or $platform is used to migrate to ${target_name} and ${platform}
Is there anything I can reuse to generate such warnings?

[yonaskolb]

That would be great. Warnings would come from a linter which is not yet implemented and tracked here #214

[tomquist]

I did the necessary change and also added warnings for old usage of $target_name and $platform. @yonaskolb Could you please have a look at this? I hope my solution is fine for now until it is replaced by the more sophisticated linter solution.

[yonaskolb]

Looks good! It does the job for now. Left a couple of small comments

[tomquist]

I'll rebase the branch on master and add additional tests that combine nested templates with targetAttributes.

[tomquist]

I adjusted the parses complex nested target templates spec to also include templateAttributes.

[yonaskolb]

Great work!