diff: mark diff properly with input/output

diff/diff_test.go

@@ -64,8 +64,14 @@ func testResourceDiffStr(rd *terraform.ResourceDiff) string {
 			newResource = " (forces new resource)"
 		}
 
+		inOut := "IN "
+		if attrDiff.Type == terraform.DiffAttrOutput {
+			inOut = "OUT"
+		}
+
 		buf.WriteString(fmt.Sprintf(
-			"  %s:%s %#v => %#v%s\n",
+			"  %s %s:%s %#v => %#v%s\n",
+			inOut,
 			attrK,
 			strings.Repeat(" ", keyLen-len(attrK)),
 			attrDiff.Old,

diff/resource_builder.go

@@ -56,6 +56,7 @@ func (b *ResourceBuilder) Diff(
 		// boolean.
 		if _, ok := requiresNewSet[k]; ok {
 			attrs[k].RequiresNew = true
+			attrs[k].Type = terraform.DiffAttrInput
 			requiresNew = true
 		}
 	}
@@ -67,6 +68,7 @@ func (b *ResourceBuilder) Diff(
 			Old:         s.ID,
 			NewComputed: true,
 			RequiresNew: true,
+			Type:        terraform.DiffAttrOutput,
 		}
 
 		for _, k := range b.CreateComputedAttrs {
@@ -74,6 +76,7 @@ func (b *ResourceBuilder) Diff(
 			attrs[k] = &terraform.ResourceAttrDiff{
 				Old:         old,
 				NewComputed: true,
+				Type:        terraform.DiffAttrOutput,
 			}
 		}
 	}

diff/resource_builder_test.go

@@ -145,23 +145,23 @@ func TestResourceBuilder_vars(t *testing.T) {
 }
 
 const testRBNewDiff = `CREATE
-  foo:        "" => "bar"
-  id:         "" => "<computed>" (forces new resource)
-  private_ip: "" => "<computed>"
+  IN  foo:        "" => "bar"
+  OUT id:         "" => "<computed>" (forces new resource)
+  OUT private_ip: "" => "<computed>"
 `
 
 const testRBRequiresNewDiff = `CREATE
-  ami:        "foo" => "bar" (forces new resource)
-  id:         "1" => "<computed>" (forces new resource)
-  private_ip: "127.0.0.1" => "<computed>"
+  IN  ami:        "foo" => "bar" (forces new resource)
+  OUT id:         "1" => "<computed>" (forces new resource)
+  OUT private_ip: "127.0.0.1" => "<computed>"
 `
 
 const testRBUnknownDiff = `CREATE
-  foo: "" => "${var.unknown}"
-  id:  "" => "<computed>" (forces new resource)
+  IN  foo: "" => "${var.unknown}"
+  OUT id:  "" => "<computed>" (forces new resource)
 `
 
 const testRBVarsDiff = `CREATE
-  foo: "" => "bar"
-  id:  "" => "<computed>" (forces new resource)
+  IN  foo: "" => "bar"
+  OUT id:  "" => "<computed>" (forces new resource)
 `

terraform/diff.go

@@ -155,8 +155,22 @@ type ResourceAttrDiff struct {
 	New         string // New Value
 	NewComputed bool   // True if new value is computed (unknown currently)
 	RequiresNew bool   // True if change requires new resource
+	Type        DiffAttrType
 }
 
+// DiffAttrType is an enum type that says whether a resource attribute
+// diff is an input attribute (comes from the configuration) or an
+// output attribute (comes as a result of applying the configuration). An
+// example input would be "ami" for AWS and an example output would be
+// "private_ip".
+type DiffAttrType byte
+
+const (
+	DiffAttrUnknown DiffAttrType = iota
+	DiffAttrInput
+	DiffAttrOutput
+)
+
 // Empty returns true if this diff encapsulates no changes.
 // TODO(mitchellh): test
 func (d *ResourceDiff) Empty() bool {