Allow specifying a StringSlice destination for StringSliceFlag

[davidsbond]

What type of PR is this?

• bug
• cleanup
• documentation
• feature

What this PR does / why we need it:

Adds a Destination field to the StringSliceFlag of type StringSlice so that we can use a variable to access the value rather than calling c.StringSlice. This adds some additional type safety and can help to avoid scenarios where you have typos calling the c.StringSlice("name") method.

Which issue(s) this PR fixes:

Fixes #1075

Testing

By running the code I've seen that the Destination gets set, I've also added in some tests for setting the destination value from env and from flags

Release Notes

Adds destination field to StringSliceFlag

[codecov]

Codecov Report

Merging #1078 into master will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1078      +/-   ##
==========================================
+ Coverage   72.83%   72.91%   +0.07%     
==========================================
  Files          33       33              
  Lines        2474     2481       +7     
==========================================
+ Hits         1802     1809       +7     
  Misses        565      565              
  Partials      107      107              

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[davidsbond]

I've found a bug in this code so far. The problem is that when you provide both environment variables and flags, you end up appending to the array instead of replacing one with the other. For example:

Environment: [a, b, c]
Flags: [1, 2, 3]
Result: [a,b,c,1,2,3]

[davidsbond]

I think I've solved it, but I'm going to do some more testing.

[davidsbond]

Based on my local testing this now works as expected, flags will override the slice set by env vars entirely.

[davidsbond]

package main

import (
	"fmt"
	"github.com/davidsbond/cli"
	"log"
	"os"
)

var (
	dest = &cli.StringSlice{}
)

func main() {
	os.Setenv("TEST_THIS_THING", "1,2,3")

	app := cli.NewApp()
	app.Action = run
	app.Flags = []cli.Flag{
		&cli.StringSliceFlag{
			Name:        "test",
			Destination: dest,
			EnvVars:     []string{"TEST_THIS_THING"},
		},
	}

	if err := app.Run(os.Args); err != nil {
		log.Fatal(err)
	}
}

func run(c *cli.Context) error {
	fmt.Println(dest.Value())
	return nil
}

go run main.go --test=a,b,c
[a,b,c]
go run main.go  
[1 2 3]

[coilysiren]

I don't have any particular opinions about the env var handling, but everything else LGTM! 🚢