hclwrite: Allow removing attributes and blocks from bodies

Previously we allowed adding both attributes and blocks, and we allowed
updating attributes, but we had no mechanism to surgically remove
attributes and blocks altogether.

hclwrite/ast_body.go

@@ -84,15 +84,33 @@ func (b *Body) GetAttribute(name string) *Attribute {
  return nil
 }
 
+// getAttributeNode is like GetAttribute but it returns the node containing
+// the selected attribute (if one is found) rather than the attribute itself.
+func (b *Body) getAttributeNode(name string) *node {
+ for n := range b.items {
+ if attr, isAttr := n.content.(*Attribute); isAttr {
+ nameObj := attr.name.content.(*identifier)
+ if nameObj.hasName(name) {
+ // We've found it!
+ return n
+ }
+ }
+ }
+
+ return nil
+}
+
 // FirstMatchingBlock returns a first matching block from the body that has the
 // given name and labels or returns nil if there is currently no matching
 // block.
 func (b *Body) FirstMatchingBlock(typeName string, labels []string) *Block {
  for _, block := range b.Blocks() {
  if typeName == block.Type() {
  labelNames := block.Labels()
+ if len(labels) == 0 && len(labelNames) == 0 {
+ return block
+ }
  if reflect.DeepEqual(labels, labelNames) {
- // We've found it!
  return block
  }
  }
@@ -101,6 +119,21 @@ func (b *Body) FirstMatchingBlock(typeName string, labels []string) *Block {
  return nil
 }
 
+// RemoveBlock removes the given block from the body, if it's in that body.
+// If it isn't present, this is a no-op.
+//
+// Returns true if it removed something, or false otherwise.
+func (b *Body) RemoveBlock(block *Block) bool {
+ for n := range b.items {
+ if n.content == block {
+ n.Detach()
+ b.items.Remove(n)
+ return true
+ }
+ }
+ return false
+}
+
 // SetAttributeValue either replaces the expression of an existing attribute
 // of the given name or adds a new attribute definition to the end of the block.
 //
@@ -143,6 +176,20 @@ func (b *Body) SetAttributeTraversal(name string, traversal hcl.Traversal) *Attr
  return attr
 }
 
+// RemoveAttribute removes the attribute with the given name from the body.
+//
+// The return value is the attribute that was removed, or nil if there was
+// no such attribute (in which case the call was a no-op).
+func (b *Body) RemoveAttribute(name string) *Attribute {
+ node := b.getAttributeNode(name)
+ if node == nil {
+ return nil
+ }
+ node.Detach()
+ b.items.Remove(node)
+ return node.content.(*Attribute)
+}
+
 // AppendBlock appends an existing block (which must not be already attached
 // to a body) to the end of the receiving body.
 func (b *Body) AppendBlock(block *Block) *Block {