Add resource sums to terraform plan

[radeksimko]

Closes #2355

Test plan

sample.tf

provider "aws" {
  access_key = ""
  secret_key = ""
  region = "${var.aws_region}"
}

resource "aws_vpc" "main" {
  cidr_block = "10.0.1.0/16"
}

resource "aws_instance" "web" {
    ami = "ami-1234"
    instance_type = "m1.small"
}

$ terraform plan # 2 to add, 0 to change, 0 to destroy

$ terraform plan -target=aws_vpc.main # 1 to add, 0 to change, 0 to destroy

$ terraform plan -destroy # 0 to add, 0 to change, 0 to destroy

$ terraform apply
$ # change aws_vpc.main.cidr_block
$ terraform plan # 0 to add, 1 to change, 0 to destroy

$ terraform plan -destroy # 0 to add, 0 to change, 2 to destroy

$ terraform plan -destroy -target=aws_instance.web # 0 to add, 0 to change, 1 to destroy

[phinze]

You can avoid the local vars by initializing the PlanSums struct empty here and incrementing its fields in the loop below, since they'll each start at zero.

[radeksimko]

Ah, good point! 👍 Thanks! I will change that.

[radeksimko]

Fixed.

[phinze]

Ah yes I've been meaning to do this!

@mitchellh is there an alternative strategy for counting these fields using hooks - or is the loop over modules easiest here?

[radeksimko]

@phinze I was first looking at hooks actually.

I thought the reason for using hooks was because both apply, destroy, refresh etc. are expensive operations and there's no such easy way of counting real resources unless we'd buffer the output somewhere - i.e. we have to wait for provider's API response and then decide what to do on per-resource-basis.

Although I can imagine that a solution using hooks might look slightly cleaner.

[phinze]

These fields default to their zero values, but the extra clarity doesn't hurt. 👍

[phinze]

LGTM! Merge at will.

[mitchellh]

I think it'd definitely be cleaner to do this with hooks. You can hook into PostDiff and do almost the same logic as is shown here, but in there.

I'd prefer that, but don't mind if this is merged as a stop-gap until then.

[radeksimko]

@mitchellh Agreed, to be honest, I just struggled to find the right hook.

It's now reworked & using PostDiff hook and it feels so much cleaner 🚿 + it will be easier to use this for potential sanity check in the future (i.e. expected to change x, but changed y in reality) since these things now share the namespace.

Will anyone of you two give a final 👍 / 👎 , please? :)

[phinze]

Ooo much nicer. LGTM

[mitchellh]

Much cleaner :)

[ghost]

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