From 7b11acde6c2826af5c51ca67802f20ad3592ad1d Mon Sep 17 00:00:00 2001
From: Sarath Francis <sarathfrancis90@gmail.com>
Date: Mon, 1 Jun 2026 22:38:21 -0400
Subject: [PATCH] Fix Node#rangeBy() ignoring index 0

When calling Node#rangeBy() (and therefore Node#error() and
Node#warn()) with index 0, the resulting range covered the whole node
instead of a single character at offset 0.

The end-of-range branch used a truthy check on opts.index, so an index
of 0 fell through and left the end position at the node's end. This is
the same off-by-zero issue that was previously fixed for endIndex; the
index branches were missed. Switch both index checks to a numeric type
check, matching the existing endIndex handling.

index 0 now produces a single-character range, consistent with every
other index value.
---
 lib/node.js          |  4 ++--
 test/node.test.ts    | 10 ++++++++++
 test/warning.test.ts |  9 +++++++++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/lib/node.js b/lib/node.js
index b403b7136..cfddbbefa 100644
--- a/lib/node.js
+++ b/lib/node.js
@@ -298,7 +298,7 @@ class Node {
           line: opts.start.line,
           offset: sourceOffset(inputString, opts.start)
         }
-      } else if (opts.index) {
+      } else if (typeof opts.index === 'number') {
         start = this.positionInside(opts.index)
       }
 
@@ -310,7 +310,7 @@ class Node {
         }
       } else if (typeof opts.endIndex === 'number') {
         end = this.positionInside(opts.endIndex)
-      } else if (opts.index) {
+      } else if (typeof opts.index === 'number') {
         end = this.positionInside(opts.index + 1)
       }
     }
diff --git a/test/node.test.ts b/test/node.test.ts
index 41b0ac7b7..1a2f33655 100755
--- a/test/node.test.ts
+++ b/test/node.test.ts
@@ -849,6 +849,16 @@ test('rangeBy() returns range for index and endIndex', () => {
   })
 })
 
+test('rangeBy() returns range for index 0', () => {
+  let css = parse('a {  one: X  }')
+  let a = css.first as Rule
+  let one = a.first as Declaration
+  equal(one.rangeBy({ index: 0 }), {
+    end: { column: 7, line: 1, offset: 6 },
+    start: { column: 6, line: 1, offset: 5 }
+  })
+})
+
 test('rangeBy() returns range for index and endIndex when offsets are missing', () => {
   let css = parse('a {  one: X  }')
   let a = css.first as Rule
diff --git a/test/warning.test.ts b/test/warning.test.ts
index 609b056aa..4075f8a7a 100644
--- a/test/warning.test.ts
+++ b/test/warning.test.ts
@@ -121,6 +121,15 @@ test('gets range from index', () => {
   is(warning.endColumn, 4)
 })
 
+test('gets range from index 0', () => {
+  let root = parse('a b{}')
+  let warning = new Warning('text', { index: 0, node: root.first })
+  is(warning.line, 1)
+  is(warning.column, 1)
+  is(warning.endLine, 1)
+  is(warning.endColumn, 2)
+})
+
 test('gets range from index and endIndex', () => {
   let root = parse('a b{}')
   let warning = new Warning('text', { endIndex: 3, index: 2, node: root.first })