feat: add newline filter

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
+```

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'
+}

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')
+    })
+  })
 })