feat(toolkit): add '--reuse-asset' option

[rix0rrr]

Reusing assets avoids rebuilding an asset and just reuses the currently
deployed one. Especially helpful for Docker containers that take a long
time to build.

Fixes #1916

---

Pull Request Checklist

• Testing
  • Unit test added (prefer not to modify an existing test, otherwise, it's probably a breaking change)
  • CLI change?: coordinate update of integration tests with team
  • cdk-init template change?: coordinated update of integration tests with team
• Docs
  • jsdocs: All public APIs documented
  • README: README and/or documentation topic updated
• Title and Description
  • Change type: title prefixed with fix, feat will appear in changelog
  • Title: use lower-case and doesn't end with a period
  • Breaking?: last paragraph: "BREAKING CHANGE: <describe what changed + link for details>"
  • Issues: Indicate issues fixed via: "Fixes #xxx" or "Closes #xxx"
• Sensitive Modules (requires 2 PR approvers)
  • IAM Policy Document (in @aws-cdk/aws-iam)
  • EC2 Security Groups and ACLs (in @aws-cdk/aws-ec2)
  • Grant APIs (only if not based on official documentation with a reference)

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license.

[eladb]

Maybe this should just be --no-build. @sam-goodwin is planning to add a distinct "build" command to the toolkit, so I envision deploy --no-build to have the effect you want with less ugliness...

[rix0rrr]

I actually had --no-build, but yargs forces interpretation of the --no- prefix to make the thing boolean. So I had to change the name.

And ultimately, I prefer the name to be positive, so you don't have the problem with double negatives.

[eladb]

you just specify build as a boolean option with a default true. it is also common to indicate in the description to use --no-build to disable.

--build and --no-build feel much more forward looking and less a hack than the current approach.

[rix0rrr]

So you propose to either build all assets or no assets?

Wouldn't have helped me in my case though, where I did want to update a Lambda but did not want to rebuild the Docker image.

I explicitly chose for selective control over which asset gets reused.

[rix0rrr]

And I agree with the "hack" terminology insofar as that the id is unpredictable. What I actually wanted was to reuse/not reuse by construct path, including glob support; but the metadata didn't have the construct path and I wanted to get a fix to the pipeline out, so I opted for selecting by the identifier that was already there.

[eladb]

got it. So how about --build-exclude instead of reuse-assets? I really think the terminology should be around "build".