added

vendor/github.com/zclconf/go-cty/cty/walk.go

@@ -0,0 +1,238 @@
+package cty
+
+// Walk visits all of the values in a possibly-complex structure, calling
+// a given function for each value.
+//
+// For example, given a list of strings the callback would first be called
+// with the whole list and then called once for each element of the list.
+//
+// The callback function may prevent recursive visits to child values by
+// returning false. The callback function my halt the walk altogether by
+// returning a non-nil error. If the returned error is about the element
+// currently being visited, it is recommended to use the provided path
+// value to produce a PathError describing that context.
+//
+// The path passed to the given function may not be used after that function
+// returns, since its backing array is re-used for other calls.
+func Walk(val Value, cb func(Path, Value) (bool, error)) error {
+	var path Path
+	return walk(path, val, cb)
+}
+
+func walk(path Path, val Value, cb func(Path, Value) (bool, error)) error {
+	deeper, err := cb(path, val)
+	if err != nil {
+		return err
+	}
+	if !deeper {
+		return nil
+	}
+
+	if val.IsNull() || !val.IsKnown() {
+		// Can't recurse into null or unknown values, regardless of type
+		return nil
+	}
+
+	// The callback already got a chance to see the mark in our
+	// call above, so can safely strip it off here in order to
+	// visit the child elements, which might still have their own marks.
+	rawVal, _ := val.Unmark()
+
+	ty := val.Type()
+	switch {
+	case ty.IsObjectType():
+		for it := rawVal.ElementIterator(); it.Next(); {
+			nameVal, av := it.Element()
+			path := append(path, GetAttrStep{
+				Name: nameVal.AsString(),
+			})
+			err := walk(path, av, cb)
+			if err != nil {
+				return err
+			}
+		}
+	case rawVal.CanIterateElements():
+		for it := rawVal.ElementIterator(); it.Next(); {
+			kv, ev := it.Element()
+			path := append(path, IndexStep{
+				Key: kv,
+			})
+			err := walk(path, ev, cb)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// Transformer is the interface used to optionally transform values in a
+// possibly-complex structure. The Enter method is called before traversing
+// through a given path, and the Exit method is called when traversal of a
+// path is complete.
+//
+// Use Enter when you want to transform a complex value before traversal
+// (preorder), and Exit when you want to transform a value after traversal
+// (postorder).
+//
+// The path passed to the given function may not be used after that function
+// returns, since its backing array is re-used for other calls.
+type Transformer interface {
+	Enter(Path, Value) (Value, error)
+	Exit(Path, Value) (Value, error)
+}
+
+type postorderTransformer struct {
+	callback func(Path, Value) (Value, error)
+}
+
+func (t *postorderTransformer) Enter(p Path, v Value) (Value, error) {
+	return v, nil
+}
+
+func (t *postorderTransformer) Exit(p Path, v Value) (Value, error) {
+	return t.callback(p, v)
+}
+
+// Transform visits all of the values in a possibly-complex structure,
+// calling a given function for each value which has an opportunity to
+// replace that value.
+//
+// Unlike Walk, Transform visits child nodes first, so for a list of strings
+// it would first visit the strings and then the _new_ list constructed
+// from the transformed values of the list items.
+//
+// This is useful for creating the effect of being able to make deep mutations
+// to a value even though values are immutable. However, it's the responsibility
+// of the given function to preserve expected invariants, such as homogenity of
+// element types in collections; this function can panic if such invariants
+// are violated, just as if new values were constructed directly using the
+// value constructor functions. An easy way to preserve invariants is to
+// ensure that the transform function never changes the value type.
+//
+// The callback function may halt the walk altogether by
+// returning a non-nil error. If the returned error is about the element
+// currently being visited, it is recommended to use the provided path
+// value to produce a PathError describing that context.
+//
+// The path passed to the given function may not be used after that function
+// returns, since its backing array is re-used for other calls.
+func Transform(val Value, cb func(Path, Value) (Value, error)) (Value, error) {
+	var path Path
+	return transform(path, val, &postorderTransformer{cb})
+}
+
+// TransformWithTransformer allows the caller to more closely control the
+// traversal used for transformation. See the documentation for Transformer for
+// more details.
+func TransformWithTransformer(val Value, t Transformer) (Value, error) {
+	var path Path
+	return transform(path, val, t)
+}
+
+func transform(path Path, val Value, t Transformer) (Value, error) {
+	val, err := t.Enter(path, val)
+	if err != nil {
+		return DynamicVal, err
+	}
+
+	ty := val.Type()
+	var newVal Value
+
+	// We need to peel off any marks here so that we can dig around
+	// inside any collection values. We'll reapply these to any
+	// new collections we construct, but the transformer's Exit
+	// method gets the final say on what to do with those.
+	rawVal, marks := val.Unmark()
+
+	switch {
+
+	case val.IsNull() || !val.IsKnown():
+		// Can't recurse into null or unknown values, regardless of type
+		newVal = val
+
+	case ty.IsListType() || ty.IsSetType() || ty.IsTupleType():
+		l := rawVal.LengthInt()
+		switch l {
+		case 0:
+			// No deep transform for an empty sequence
+			newVal = val
+		default:
+			elems := make([]Value, 0, l)
+			for it := rawVal.ElementIterator(); it.Next(); {
+				kv, ev := it.Element()
+				path := append(path, IndexStep{
+					Key: kv,
+				})
+				newEv, err := transform(path, ev, t)
+				if err != nil {
+					return DynamicVal, err
+				}
+				elems = append(elems, newEv)
+			}
+			switch {
+			case ty.IsListType():
+				newVal = ListVal(elems).WithMarks(marks)
+			case ty.IsSetType():
+				newVal = SetVal(elems).WithMarks(marks)
+			case ty.IsTupleType():
+				newVal = TupleVal(elems).WithMarks(marks)
+			default:
+				panic("unknown sequence type") // should never happen because of the case we are in
+			}
+		}
+
+	case ty.IsMapType():
+		l := rawVal.LengthInt()
+		switch l {
+		case 0:
+			// No deep transform for an empty map
+			newVal = val
+		default:
+			elems := make(map[string]Value)
+			for it := rawVal.ElementIterator(); it.Next(); {
+				kv, ev := it.Element()
+				path := append(path, IndexStep{
+					Key: kv,
+				})
+				newEv, err := transform(path, ev, t)
+				if err != nil {
+					return DynamicVal, err
+				}
+				elems[kv.AsString()] = newEv
+			}
+			newVal = MapVal(elems).WithMarks(marks)
+		}
+
+	case ty.IsObjectType():
+		switch {
+		case ty.Equals(EmptyObject):
+			// No deep transform for an empty object
+			newVal = val
+		default:
+			atys := ty.AttributeTypes()
+			newAVs := make(map[string]Value)
+			for name := range atys {
+				av := val.GetAttr(name)
+				path := append(path, GetAttrStep{
+					Name: name,
+				})
+				newAV, err := transform(path, av, t)
+				if err != nil {
+					return DynamicVal, err
+				}
+				newAVs[name] = newAV
+			}
+			newVal = ObjectVal(newAVs).WithMarks(marks)
+		}
+
+	default:
+		newVal = val
+	}
+
+	newVal, err = t.Exit(path, newVal)
+	if err != nil {
+		return DynamicVal, err
+	}
+	return newVal, err
+}