Add buildpack create command to generate new buildpack scaffolding

[jkutner]

Summary

Generates the basic files needed for a buildpack written in Bash:

• buildpack.toml
• bin/build
• bin/detect

Output

Before

N/A

After

$ pack buildpack new foobar
    create buildpack.toml
    create bin/build
    create bin/detect
Successfully created foobar

Documentation

• Should this change be documented?
  • Yes, see #___
  • No

Related

Resolves #82 (finally! 😄 )
buildpacks/rfcs#136

[ekcasey]

@jkutner I assume this is scaffolding for a Bash buildpack? I worry somewhat that he existence of this command will encourage folks to write complex buildpacks in Bash, which may not be a pleasant experience in the long run.

[jkutner]

@ekcasey no, there's a --language option, which can support Golang. I've been looking at golang buildpacks to try and figure out what an opinionated scaffold would look like, but I'd love to get some help from people who actually right buildpacks in Go.

Sidenote: I disagree about bash "not be a pleasant experience in the long run". Many buildpacks v2 are written in bash and have been successful and well maintained for years.

[codecov]

Codecov Report

Merging #1025 (c638eb8) into main (658dec2) will decrease coverage by 0.18%.
The diff coverage is 68.87%.

@@            Coverage Diff             @@
##             main    #1025      +/-   ##
==========================================
- Coverage   80.56%   80.39%   -0.17%     
==========================================
  Files         131      133       +2     
  Lines        8050     8156     +106     
==========================================
+ Hits         6485     6556      +71     
- Misses       1147     1171      +24     
- Partials      418      429      +11     

Flag	Coverage Δ
os_linux	?
os_macos	77.34% <71.96%> (-0.07%)	⬇️
os_windows	80.33% <68.87%> (-0.15%)	⬇️
unit	77.34% <71.96%> (-2.62%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[dfreilich]

nit: if we don't need the rest of the client, does it make more sense to just pass the logger?

[dfreilich]

Should this be flag.Path? Otherwise, assuming they're passing in a string, I don't see how this if block can be reached.

[jkutner]

Fixed in 9e20ac0

[jromero]

@jkutner found a few oddities when trying to use this command. Would you mind addressing them?

⚠️ Acceptance

⚠️ pack help buildpacks new

For the --api flag, it states "Platform API" when it should be "Buildpack API"

pack-dev help buildpack new
buildpack new generates the basic scaffolding of a buildpack repository. It creates a new directory `name` in the current directory (or at `path`, if passed as a flag), and initializes a buildpack.toml, and two executable bash scripts, `bin/detect` and `bin/build`.

Usage:
  pack buildpack new <id> [flags]

Examples:
pack buildpack new sample/my-buildpack

Flags:
  -a, --api string       Platform API compatibility of the generated buildpack (default "0.4")
  -h, --help             Help for 'new'
  -p, --path string      Path to generate the buildpack
  -s, --stacks strings   Stack(s) this buildpack will be compatible with
                         Repeat for each stack in order, or supply once by comma-separated list (default [io.buildpacks.stacks.bionic])
  -V, --version string   Version of the generated buildpack (default "1.0.0")

Global Flags:
      --no-color     Disable color output
  -q, --quiet        Show less output
      --timestamps   Enable timestamps in output
  -v, --verbose      Show more output

⚠️ pack buildpacks new -p ...

I would have expected the path flag (--path) to allow me to rename the final directory. This doesn't seem to be the case.

In the example below I expected the buildpack to be created at my-bp-folder not my-bp-folder/my-bp

❯ ls -1

/tmp on ☁️ rjavier@vmware.com
❯ pack-dev buildpack new my-bp -p my-bp-folder
    create  buildpack.toml
    create  bin/build
    create  bin/detect
Successfully created my-bp

/tmp on ☁️ rjavier@vmware.com
❯ ls -1
my-bp-folder/

/tmp on ☁️ rjavier@vmware.com
❯ ls -1 my-bp-folder/
my-bp/

/tmp on ☁️ rjavier@vmware.com
❯ ls -1 my-bp-folder/my-bp/
bin/
buildpack.toml

⚠️ pack buildpacks new (to existing directory)

When an directory is present that collides with the name of the buildpack nothing is created and no message is provided.

Expected:

• If directory is empty, for the buildpack to be created.
• If directory has files, for it to output an error message.

/tmp/test-1026 on ☁️ rjavier@vmware.com
❯ mkdir my-bp

/tmp/test-1026 on ☁️ rjavier@vmware.com
❯ pack-dev buildpack new my-bp

/tmp/test-1026 on ☁️ rjavier@vmware.com
❯ ls -1
my-bp/

/tmp/test-1026 on ☁️ rjavier@vmware.com
❯ ls -1 my-bp/

[jkutner]

@jromero fixed all three issues

[jromero]

@jkutner, verified issues above were resolved. Left a single nitpick but feel free to merge.

absentee