Allow the use of build.name for naming provisioners and post-processors

[nywilken]

This changes makes the builder variable build.name avialable at parsing so that it can be used to name provisioners and post-processors.

source "null" "pizza" {
    communicator = "none"
}

build {
    name = "pineapple"
    sources = [
        "sources.null.pizza",
    ]

    provisioner "shell-local" {
        name = "${build.name}"
        inline = [
            "echo '' > ${build.name}.txt"
        ]
    }
    post-processor "shell-local" {
        name = "${build.name}"
        inline = [
            "echo '' > ${build.name}-pps.txt"
        ]
    }
}

Closes #11411

[sylviamoss]

You could have also passed the extra variables as argument here, like:

Suggested change

	ectx := cfg.EvalContext(BuildContext, nil)
	ectx.Variables[buildAccessor] = cty.ObjectVal(map[string]cty.Value{
	"name": cty.StringVal(b.Name),
	})
	variables := map[string]cty.Value{
	buildAccessor: cty.ObjectVal(map[string]cty.Value{
	"name": cty.StringVal(b.Name),
	}),
	}
	ectx := cfg.EvalContext(BuildContext, variables)

It looks bigger, just another possibility. Don't feel pressured to accept the changes. Yours looks great!

[sylviamoss]

LGTM 👍🏼

[azr]

LGTM, good catch !

[github-actions]

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