hclwrite: Allow updating block type and labels

Fixes #338

Add methods to update block type and labels to enable us to refactor HCL
configurations such as renaming Terraform resources.

- `*Block.SetType(typeName string)`
- `*Block.SetLabels(labels []string)`

Some additional notes about SetLabels:

Since we cannot assume that old and new labels are equal in length,
remove old labels and insert new ones before TokenOBrace.

To implement this, I also added the following methods.

- `*nodes.Insert(pos *node, c nodeContent) *node`
- `*nodes.InsertNode(pos *node, n *node) *node`

They are similar to the existing Append / AppendNode,
but insert a node before a given position.

hclwrite/ast_block.go

@@ -79,6 +79,13 @@ func (b *Block) Type() string {
 	return string(typeNameObj.token.Bytes)
 }
 
+// SetType updates the type name of the block to a given name.
+func (b *Block) SetType(typeName string) {
+	nameTok := newIdentToken(typeName)
+	nameObj := newIdentifier(nameTok)
+	b.typeName.ReplaceWith(nameObj)
+}
+
 // Labels returns the labels of the block.
 func (b *Block) Labels() []string {
 	labelNames := make([]string, 0, len(b.labels))
@@ -116,3 +123,25 @@ func (b *Block) Labels() []string {
 
 	return labelNames
 }
+
+// SetLabels updates the labels of the block to given labels.
+// Since we cannot assume that old and new labels are equal in length,
+// remove old labels and insert new ones before TokenOBrace.
+func (b *Block) SetLabels(labels []string) {
+	// Remove old labels
+	for oldLabel := range b.labels {
+		oldLabel.Detach()
+		b.labels.Remove(oldLabel)
+	}
+
+	// Insert new labels before TokenOBrace.
+	for _, label := range labels {
+		labelToks := TokensForValue(cty.StringVal(label))
+		// Force a new label to use the quoted form even if the old one is unquoted.
+		// The unquoted form is supported in HCL 2 only for compatibility with some
+		// historical use in HCL 1.
+		labelObj := newQuoted(labelToks)
+		labelNode := b.children.Insert(b.open, labelObj)
+		b.labels.Add(labelNode)
+	}
+}

hclwrite/ast_block_test.go

@@ -6,7 +6,10 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/davecgh/go-spew/spew"
+	"github.com/google/go-cmp/cmp"
 	"github.com/hashicorp/hcl/v2"
+	"github.com/hashicorp/hcl/v2/hclsyntax"
 )
 
 func TestBlockType(t *testing.T) {
@@ -103,3 +106,310 @@ escape "\u0041" {
 		})
 	}
 }
+
+func TestBlockSetType(t *testing.T) {
+	tests := []struct {
+		src         string
+		oldTypeName string
+		newTypeName string
+		labels      []string
+		want        Tokens
+	}{
+		{
+			"foo {}",
+			"foo",
+			"bar",
+			nil,
+			Tokens{
+				{
+					Type:         hclsyntax.TokenIdent,
+					Bytes:        []byte(`bar`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOBrace,
+					Bytes:        []byte{'{'},
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenCBrace,
+					Bytes:        []byte{'}'},
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenEOF,
+					Bytes:        []byte{},
+					SpacesBefore: 0,
+				},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("%s %s %s in %s", test.oldTypeName, test.newTypeName, test.labels, test.src), func(t *testing.T) {
+			f, diags := ParseConfig([]byte(test.src), "", hcl.Pos{Line: 1, Column: 1})
+			if len(diags) != 0 {
+				for _, diag := range diags {
+					t.Logf("- %s", diag.Error())
+				}
+				t.Fatalf("unexpected diagnostics")
+			}
+
+			b := f.Body().FirstMatchingBlock(test.oldTypeName, test.labels)
+			b.SetType(test.newTypeName)
+			got := f.BuildTokens(nil)
+			format(got)
+			if !reflect.DeepEqual(got, test.want) {
+				diff := cmp.Diff(test.want, got)
+				t.Errorf("wrong result\ngot:  %s\nwant: %s\ndiff:\n%s", spew.Sdump(got), spew.Sdump(test.want), diff)
+			}
+		})
+	}
+}
+
+func TestBlockSetLabels(t *testing.T) {
+	tests := []struct {
+		src       string
+		typeName  string
+		oldLabels []string
+		newLabels []string
+		want      Tokens
+	}{
+		{
+			`foo "hoge" {}`,
+			"foo",
+			[]string{"hoge"},
+			[]string{"fuga"}, // update first label
+			Tokens{
+				{
+					Type:         hclsyntax.TokenIdent,
+					Bytes:        []byte(`foo`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOQuote,
+					Bytes:        []byte(`"`),
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenQuotedLit,
+					Bytes:        []byte(`fuga`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenCQuote,
+					Bytes:        []byte(`"`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOBrace,
+					Bytes:        []byte{'{'},
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenCBrace,
+					Bytes:        []byte{'}'},
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenEOF,
+					Bytes:        []byte{},
+					SpacesBefore: 0,
+				},
+			},
+		},
+		{
+			`foo "hoge" "fuga" {}`,
+			"foo",
+			[]string{"hoge", "fuga"},
+			[]string{"hoge", "piyo"}, // update second label
+			Tokens{
+				{
+					Type:         hclsyntax.TokenIdent,
+					Bytes:        []byte(`foo`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOQuote,
+					Bytes:        []byte(`"`),
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenQuotedLit,
+					Bytes:        []byte(`hoge`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenCQuote,
+					Bytes:        []byte(`"`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOQuote,
+					Bytes:        []byte(`"`),
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenQuotedLit,
+					Bytes:        []byte(`piyo`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenCQuote,
+					Bytes:        []byte(`"`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOBrace,
+					Bytes:        []byte{'{'},
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenCBrace,
+					Bytes:        []byte{'}'},
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenEOF,
+					Bytes:        []byte{},
+					SpacesBefore: 0,
+				},
+			},
+		},
+		{
+			`foo {}`,
+			"foo",
+			[]string{},
+			[]string{"fuga"}, // insert a new label to empty list
+			Tokens{
+				{
+					Type:         hclsyntax.TokenIdent,
+					Bytes:        []byte(`foo`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOQuote,
+					Bytes:        []byte(`"`),
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenQuotedLit,
+					Bytes:        []byte(`fuga`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenCQuote,
+					Bytes:        []byte(`"`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOBrace,
+					Bytes:        []byte{'{'},
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenCBrace,
+					Bytes:        []byte{'}'},
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenEOF,
+					Bytes:        []byte{},
+					SpacesBefore: 0,
+				},
+			},
+		},
+		{
+			`foo "hoge" {}`,
+			"foo",
+			[]string{"hoge"},
+			[]string{}, // remove all labels
+			Tokens{
+				{
+					Type:         hclsyntax.TokenIdent,
+					Bytes:        []byte(`foo`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOBrace,
+					Bytes:        []byte{'{'},
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenCBrace,
+					Bytes:        []byte{'}'},
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenEOF,
+					Bytes:        []byte{},
+					SpacesBefore: 0,
+				},
+			},
+		},
+		{
+			`foo hoge {}`,
+			"foo",
+			[]string{"hoge"},
+			[]string{"fuga"}, // force quoted form even if the old one is unquoted.
+			Tokens{
+				{
+					Type:         hclsyntax.TokenIdent,
+					Bytes:        []byte(`foo`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOQuote,
+					Bytes:        []byte(`"`),
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenQuotedLit,
+					Bytes:        []byte(`fuga`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenCQuote,
+					Bytes:        []byte(`"`),
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenOBrace,
+					Bytes:        []byte{'{'},
+					SpacesBefore: 1,
+				},
+				{
+					Type:         hclsyntax.TokenCBrace,
+					Bytes:        []byte{'}'},
+					SpacesBefore: 0,
+				},
+				{
+					Type:         hclsyntax.TokenEOF,
+					Bytes:        []byte{},
+					SpacesBefore: 0,
+				},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("%s %s %s in %s", test.typeName, test.oldLabels, test.newLabels, test.src), func(t *testing.T) {
+			f, diags := ParseConfig([]byte(test.src), "", hcl.Pos{Line: 1, Column: 1})
+			if len(diags) != 0 {
+				for _, diag := range diags {
+					t.Logf("- %s", diag.Error())
+				}
+				t.Fatalf("unexpected diagnostics")
+			}
+
+			b := f.Body().FirstMatchingBlock(test.typeName, test.oldLabels)
+			b.SetLabels(test.newLabels)
+			got := f.BuildTokens(nil)
+			format(got)
+			if !reflect.DeepEqual(got, test.want) {
+				diff := cmp.Diff(test.want, got)
+				t.Errorf("wrong result\ngot:  %s\nwant: %s\ndiff:\n%s", spew.Sdump(got), spew.Sdump(test.want), diff)
+			}
+		})
+	}
+}

hclwrite/node.go

@@ -130,6 +130,36 @@ func (ns *nodes) AppendNode(n *node) {
 	}
 }
 
+// Insert inserts a nodeContent at a given position.
+// This is just a wrapper for InsertNode. See InsertNode for details.
+func (ns *nodes) Insert(pos *node, c nodeContent) *node {
+	n := &node{
+		content: c,
+	}
+	ns.InsertNode(pos, n)
+	n.list = ns
+	return n
+}
+
+// InsertNode inserts a node at a given position.
+// The first argument is a node reference before which to insert.
+// To insert it to an empty list, set position to nil.
+func (ns *nodes) InsertNode(pos *node, n *node) {
+	if pos == nil {
+		// inserts n to empty list.
+		ns.first = n
+		ns.last = n
+	} else {
+		// inserts n before pos.
+		pos.before.after = n
+		n.before = pos.before
+		pos.before = n
+		n.after = pos
+	}
+
+	n.list = ns
+}
+
 func (ns *nodes) AppendUnstructuredTokens(tokens Tokens) *node {
 	if len(tokens) == 0 {
 		return nil