Ensure we have all references for output preconditions

internal/terraform/context_apply2_test.go

@@ -1784,3 +1784,51 @@ resource "test_object" "y" {
 	_, diags = ctx.Apply(plan, m)
 	assertNoErrors(t, diags)
 }
+
+// ensure all references from preconditions are tracked through plan and apply
+func TestContext2Apply_preconditionErrorMessageRef(t *testing.T) {
+	p := testProvider("test")
+	ctx := testContext2(t, &ContextOpts{
+		Providers: map[addrs.Provider]providers.Factory{
+			addrs.NewDefaultProvider("test"): testProviderFuncFixed(p),
+		},
+	})
+
+	m := testModuleInline(t, map[string]string{
+		"main.tf": `
+module "nested" {
+  source = "./mod"
+}
+
+output "nested_a" {
+  value = module.nested.a
+}
+`,
+
+		"mod/main.tf": `
+variable "boop" {
+  default = "boop"
+}
+
+variable "msg" {
+  default = "Incorrect boop."
+}
+
+output "a" {
+  value     = "x"
+
+  precondition {
+    condition     = var.boop == "boop"
+    error_message = var.msg
+  }
+}
+`,
+	})
+
+	plan, diags := ctx.Plan(m, states.NewState(), &PlanOpts{
+		Mode: plans.NormalMode,
+	})
+	assertNoErrors(t, diags)
+	_, diags = ctx.Apply(plan, m)
+	assertNoErrors(t, diags)
+}

internal/terraform/node_output.go

@@ -278,19 +278,21 @@ func (n *NodeApplyableOutput) ReferenceableAddrs() []addrs.Referenceable {
 }
 
 func referencesForOutput(c *configs.Output) []*addrs.Reference {
+	var refs []*addrs.Reference
+
 	impRefs, _ := lang.ReferencesInExpr(c.Expr)
 	expRefs, _ := lang.References(c.DependsOn)
-	l := len(impRefs) + len(expRefs)
-	if l == 0 {
-		return nil
-	}
-	refs := make([]*addrs.Reference, 0, l)
+
 	refs = append(refs, impRefs...)
 	refs = append(refs, expRefs...)
+
 	for _, check := range c.Preconditions {
-		checkRefs, _ := lang.ReferencesInExpr(check.Condition)
-		refs = append(refs, checkRefs...)
+		condRefs, _ := lang.ReferencesInExpr(check.Condition)
+		refs = append(refs, condRefs...)
+		errRefs, _ := lang.ReferencesInExpr(check.ErrorMessage)
+		refs = append(refs, errRefs...)
 	}
+
 	return refs
 }