From 64c3a8f55091f52fc2eb043fb5fca39ac1f43557 Mon Sep 17 00:00:00 2001
From: James Bardin <j.bardin@gmail.com>
Date: Fri, 2 Oct 2020 11:25:21 -0400
Subject: [PATCH] lang.Scope.EvalSelfBlock

In order to properly evaluate a destroy provisioner, we cannot rely on
the usual evaluation context, because the resource has already been
removed from the state.

EvalSelfBlock evaluates an hcl.Body in the limited scope of a single
object as "self", with the added values of "count.index" and "each.key".
---
 lang/eval.go | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/lang/eval.go b/lang/eval.go
index db5a15a24..381ec4288 100644
--- a/lang/eval.go
+++ b/lang/eval.go
@@ -8,6 +8,7 @@ import (
 	"github.com/hashicorp/hcl/v2/hcldec"
 	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/configs/configschema"
+	"github.com/hashicorp/terraform/instances"
 	"github.com/hashicorp/terraform/lang/blocktoattr"
 	"github.com/hashicorp/terraform/tfdiags"
 	"github.com/zclconf/go-cty/cty"
@@ -69,6 +70,35 @@ func (s *Scope) EvalBlock(body hcl.Body, schema *configschema.Block) (cty.Value,
 	return val, diags
 }
 
+// EvalSelfBlock evaluates the given body only within the scope of the provided
+// object and instance key data. References to the object must use self, and the
+// key data will only contain count.index or each.key.
+func (s *Scope) EvalSelfBlock(body hcl.Body, self cty.Value, schema *configschema.Block, keyData instances.RepetitionData) (cty.Value, tfdiags.Diagnostics) {
+	vals := make(map[string]cty.Value)
+	vals["self"] = self
+
+	if !keyData.CountIndex.IsNull() {
+		vals["count"] = cty.ObjectVal(map[string]cty.Value{
+			"index": keyData.CountIndex,
+		})
+	}
+	if !keyData.EachKey.IsNull() {
+		vals["each"] = cty.ObjectVal(map[string]cty.Value{
+			"key": keyData.EachKey,
+		})
+	}
+
+	ctx := &hcl.EvalContext{
+		Variables: vals,
+		Functions: s.Functions(),
+	}
+
+	var diags tfdiags.Diagnostics
+	val, decDiags := hcldec.Decode(body, schema.DecoderSpec(), ctx)
+	diags = diags.Append(decDiags)
+	return val, diags
+}
+
 // EvalExpr evaluates a single expression in the receiving context and returns
 // the resulting value. The value will be converted to the given type before
 // it is returned if possible, or else an error diagnostic will be produced