outputs should not be checked during destroy

Module output may need to be evaluated during destroy in order to
possibly be used by providers. The final state however is that all
objects are destroyed, so preconditions should not be evaluated.

internal/terraform/node_output.go

@@ -20,11 +20,12 @@ import (
 // nodeExpandOutput is the placeholder for a non-root module output that has
 // not yet had its module path expanded.
 type nodeExpandOutput struct {
-	Addr        addrs.OutputValue
-	Module      addrs.Module
-	Config      *configs.Output
-	Destroy     bool
-	RefreshOnly bool
+	Addr         addrs.OutputValue
+	Module       addrs.Module
+	Config       *configs.Output
+	DestroyPlan  bool
+	DestroyApply bool
+	RefreshOnly  bool
 
 	// Planning is set to true when this node is in a graph that was produced
 	// by the plan graph builder, as opposed to the apply graph builder.
@@ -52,7 +53,7 @@ func (n *nodeExpandOutput) temporaryValue() bool {
 }
 
 func (n *nodeExpandOutput) DynamicExpand(ctx EvalContext) (*Graph, error) {
-	if n.Destroy {
+	if n.DestroyPlan {
 		// if we're planning a destroy, we only need to handle the root outputs.
 		// The destroy plan doesn't evaluate any other config, so we can skip
 		// the rest of the outputs.
@@ -105,10 +106,11 @@ func (n *nodeExpandOutput) DynamicExpand(ctx EvalContext) (*Graph, error) {
 		}
 
 		o := &NodeApplyableOutput{
-			Addr:        absAddr,
-			Config:      n.Config,
-			Change:      change,
-			RefreshOnly: n.RefreshOnly,
+			Addr:         absAddr,
+			Config:       n.Config,
+			Change:       change,
+			RefreshOnly:  n.RefreshOnly,
+			DestroyApply: n.DestroyApply,
 		}
 		log.Printf("[TRACE] Expanding output: adding %s as %T", o.Addr.String(), o)
 		g.Add(o)
@@ -192,8 +194,11 @@ func (n *nodeExpandOutput) ReferenceOutside() (selfPath, referencePath addrs.Mod
 
 // GraphNodeReferencer
 func (n *nodeExpandOutput) References() []*addrs.Reference {
-	// root outputs might be destroyable, and may not reference anything in
-	// that case
+	// DestroyNodes do not reference anything.
+	if n.Module.IsRoot() && n.DestroyApply {
+		return nil
+	}
+
 	return referencesForOutput(n.Config)
 }
 
@@ -208,6 +213,10 @@ type NodeApplyableOutput struct {
 	// Refresh-only mode means that any failing output preconditions are
 	// reported as warnings rather than errors
 	RefreshOnly bool
+
+	// DestroyApply indicates that we are applying a destroy plan, and do not
+	// need to account for conditional blocks.
+	DestroyApply bool
 }
 
 var (
@@ -321,19 +330,23 @@ func (n *NodeApplyableOutput) Execute(ctx EvalContext, op walkOperation) (diags
 		}
 	}
 
-	checkRuleSeverity := tfdiags.Error
-	if n.RefreshOnly {
-		checkRuleSeverity = tfdiags.Warning
-	}
-	checkDiags := evalCheckRules(
-		addrs.OutputPrecondition,
-		n.Config.Preconditions,
-		ctx, n.Addr, EvalDataForNoInstanceKey,
-		checkRuleSeverity,
-	)
-	diags = diags.Append(checkDiags)
-	if diags.HasErrors() {
-		return diags // failed preconditions prevent further evaluation
+	// Checks are not evaluated during a destroy. The checks may fail, may not
+	// be valid, or may not have been registered at all.
+	if !n.DestroyApply {
+		checkRuleSeverity := tfdiags.Error
+		if n.RefreshOnly {
+			checkRuleSeverity = tfdiags.Warning
+		}
+		checkDiags := evalCheckRules(
+			addrs.OutputPrecondition,
+			n.Config.Preconditions,
+			ctx, n.Addr, EvalDataForNoInstanceKey,
+			checkRuleSeverity,
+		)
+		diags = diags.Append(checkDiags)
+		if diags.HasErrors() {
+			return diags // failed preconditions prevent further evaluation
+		}
 	}
 
 	// If there was no change recorded, or the recorded change was not wholly

internal/terraform/transform_output.go

@@ -92,12 +92,13 @@ func (t *OutputTransformer) transform(g *Graph, c *configs.Config) error {
 
 		default:
 			node = &nodeExpandOutput{
-				Addr:        addr,
-				Module:      c.Path,
-				Config:      o,
-				Destroy:     t.removeRootOutputs,
-				RefreshOnly: t.RefreshOnly,
-				Planning:    t.Planning,
+				Addr:         addr,
+				Module:       c.Path,
+				Config:       o,
+				DestroyPlan:  t.removeRootOutputs,
+				DestroyApply: t.destroyApply,
+				RefreshOnly:  t.RefreshOnly,
+				Planning:     t.Planning,
 			}
 		}