From 442737fd7ced9dbbcb15b9d1804b24fd3d0d7d4a Mon Sep 17 00:00:00 2001
From: txtpbfmt team <txtpbfmt-copybara-robot@google.com>
Date: Mon, 15 Jan 2024 04:13:37 -0800
Subject: [PATCH] Add a method for checking if a node is a blank line.

PiperOrigin-RevId: 598573944
---
 ast/ast.go      |  9 ++++++-
 ast/ast_test.go | 68 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+), 1 deletion(-)

diff --git a/ast/ast.go b/ast/ast.go
index 489e9b7..1759624 100644
--- a/ast/ast.go
+++ b/ast/ast.go
@@ -207,11 +207,18 @@ func (n *Node) getChildValue(field string) *Value {
 	return nil
 }
 
-// IsCommentOnly returns true if this is a comment-only node.
+// IsCommentOnly returns true if this is a comment-only node. Even a node that
+// only contains a blank line is considered a comment-only node in the sense
+// that it has no proto content.
 func (n *Node) IsCommentOnly() bool {
 	return n.Name == "" && n.Children == nil
 }
 
+// IsBlankLine returns true if this is a blank line node.
+func (n *Node) IsBlankLine() bool {
+	return n.IsCommentOnly() && len(n.PreComments) == 1 && n.PreComments[0] == ""
+}
+
 type fixData struct {
 	inline bool
 }
diff --git a/ast/ast_test.go b/ast/ast_test.go
index b3eb171..dd2babf 100644
--- a/ast/ast_test.go
+++ b/ast/ast_test.go
@@ -185,6 +185,12 @@ bar: 2
   foo: true  # bar
 }
 # trailing comment
+`,
+			want: []bool{false, true},
+		},
+		{
+			in: `foo: 1
+
 `,
 			want: []bool{false, true},
 		},
@@ -210,6 +216,68 @@ bar: 2
 	}
 }
 
+func TestIsBlankLine(t *testing.T) {
+	inputs := []struct {
+		in   string
+		want []bool
+	}{{
+		in: `foo: 1
+bar: 2`,
+		want: []bool{false, false},
+	},
+		{
+			in: `foo: 1
+bar: 2
+`,
+			want: []bool{false, false},
+		},
+		{
+			in: `foo: 1
+bar: 2
+# A trailing comment.
+`,
+			want: []bool{false, false, false},
+		},
+		{
+			in: `first {
+  foo: true  # bar
+}
+# trailing comment
+`,
+			want: []bool{false, false},
+		},
+		{
+			in: `foo: 1
+
+`,
+			want: []bool{false, true},
+		},
+		{
+			in: `# Header comment.
+
+foo: 1
+`,
+			// The blank line is part of the node of the `foo: 1` item.
+			want: []bool{false, false},
+		},
+	}
+	for _, input := range inputs {
+		nodes, err := parser.Parse([]byte(input.in))
+		if err != nil {
+			t.Errorf("Parse %v returned err %v", input.in, err)
+			continue
+		}
+		if len(nodes) != len(input.want) {
+			t.Errorf("For %v, expect %v nodes, got %v", input.in, len(input.want), len(nodes))
+		}
+		for i, n := range nodes {
+			if got := n.IsBlankLine(); got != input.want[i] {
+				t.Errorf("For %v, nodes[%v].IsBlankLine() = %v, want %v", input.in, i, got, input.want[i])
+			}
+		}
+	}
+}
+
 func TestFixInline(t *testing.T) {
 	content := `first { }`