terraform: Diff.DeepCopy

terraform/context.go

@@ -37,6 +37,11 @@ var (
 	// contextFailOnShadowError will cause Context operations to return
 	// errors when shadow operations fail. This is only used for testing.
 	contextFailOnShadowError = false
+
+	// contextTestDeepCopyOnPlan will perform a Diff DeepCopy on every
+	// Plan operation, effectively testing the Diff DeepCopy whenever
+	// a Plan occurs. This is enabled for tests.
+	contextTestDeepCopyOnPlan = false
 )
 
 // ContextOpts are the user-configurable options to create a context with
@@ -437,6 +442,17 @@ func (c *Context) Plan() (*Plan, error) {
 	}
 	p.Diff = c.diff
 
+	// If this is true, it means we're running unit tests. In this case,
+	// we perform a deep copy just to ensure that all context tests also
+	// test that a diff is copy-able. This will panic if it fails. This
+	// is enabled during unit tests.
+	//
+	// This should never be true during production usage, but even if it is,
+	// it can't do any real harm.
+	if contextTestDeepCopyOnPlan {
+		p.Diff.DeepCopy()
+	}
+
 	// Now that we have a diff, we can build the exact graph that Apply will use
 	// and catch any possible cycles during the Plan phase.
 	if _, err := c.Graph(&ContextGraphOpts{Validate: true}); err != nil {

terraform/diff.go

@@ -9,6 +9,8 @@ import (
 	"sort"
 	"strings"
 	"sync"
+
+	"github.com/mitchellh/copystructure"
 )
 
 // DiffChangeType is an enum with the kind of changes a diff has planned.
@@ -79,6 +81,17 @@ func (d *Diff) Empty() bool {
 	return true
 }
 
+// DeepCopy performs a deep copy of all parts of the Diff, making the
+// resulting Diff safe to use without modifying this one.
+func (d *Diff) DeepCopy() *Diff {
+	copy, err := copystructure.Config{Lock: true}.Copy(d)
+	if err != nil {
+		panic(err)
+	}
+
+	return copy.(*Diff)
+}
+
 func (d *Diff) String() string {
 	var buf bytes.Buffer
 

terraform/terraform_test.go

@@ -35,6 +35,9 @@ func TestMain(m *testing.M) {
 	// Make sure shadow operations fail our real tests
 	contextFailOnShadowError = true
 
+	// Always DeepCopy the Diff on every Plan during a test
+	contextTestDeepCopyOnPlan = true
+
 	os.Exit(m.Run())
 }