From c5bc9cdb01fcea518e6a9ac6bed6b7d74b1f4c46 Mon Sep 17 00:00:00 2001
From: Edward Gibbs <edwardgibbs123@btinternet.com>
Date: Fri, 6 Mar 2026 16:41:00 +0000
Subject: [PATCH] feat: add newline filter

---
 docs/source/filters/newline.md          | 17 +++++++++++++++++
 src/filters/string.ts                   | 15 +++++++++++++++
 test/integration/filters/string.spec.ts | 14 ++++++++++++++
 3 files changed, 46 insertions(+)
 create mode 100644 docs/source/filters/newline.md

diff --git a/docs/source/filters/newline.md b/docs/source/filters/newline.md
new file mode 100644
index 0000000000..0d991ce035
--- /dev/null
+++ b/docs/source/filters/newline.md
@@ -0,0 +1,17 @@
+# newline
+
+Appends a newline (`\n`) to the input string if it does not already end with one.
+
+This is useful for scenarios where multi-line string inputs are prevented and we rely on a single line definition for the liquid template.
+
+## Example
+
+```liquid
+{{ "Hello" | newline }}World
+```
+
+Output:
+
+```
+Hello\nWorld
+```
diff --git a/src/filters/string.ts b/src/filters/string.ts
index ec163d717f..f2c0d16e88 100644
--- a/src/filters/string.ts
+++ b/src/filters/string.ts
@@ -199,3 +199,18 @@ export function array_to_sentence_string (this: FilterImpl, array: unknown[], co
       return `${array.slice(0, -1).join(', ')}, ${connector} ${array[array.length - 1]}`
   }
 }
+
+export function newline (this: FilterImpl, v: unknown) {
+  let str = stringify(v)
+
+  // Normalize windows newline
+  if (str.endsWith('\r\n')) {
+    str = str.slice(0, -2) + '\n'
+  }
+
+  this.context.memoryLimit.use(str.length + 1)
+
+  // Handle the case where newline is already added
+  if (str.endsWith('\n')) return str
+  return str + '\n'
+}
diff --git a/test/integration/filters/string.spec.ts b/test/integration/filters/string.spec.ts
index 9ea5bd0888..8a0820eeee 100644
--- a/test/integration/filters/string.spec.ts
+++ b/test/integration/filters/string.spec.ts
@@ -347,4 +347,18 @@ describe('filters/string', function () {
       expect(html).toEqual('foo, bar, and baz')
     })
   })
+  describe('newline', function () {
+    it('should add newline character', async () => {
+      const result = await liquid.parseAndRender('{{"Hello" | newline}}World')
+      expect(result).toEqual('Hello\nWorld')
+    })
+    it('should ignore existing newline characters', async () => {
+      const result = await liquid.parseAndRender('{{"Hello\n" | newline}}World')
+      expect(result).toEqual('Hello\nWorld')
+    })
+    it('should ignore windows newline characters', async () => {
+      const result = await liquid.parseAndRender('{{"Hello\r\n" | newline}}World')
+      expect(result).toEqual('Hello\nWorld')
+    })
+  })
 })