fix: count string-level appends and prepends in isEmpty

src/MagicString.ts

@@ -1043,6 +1043,9 @@ export default class MagicString {
    * Returns true if the resulting source is empty (disregarding white space).
    */
   isEmpty(): boolean {
+    // mirrors toString(): the string-level intro and outro bookend the chunks
+    if (this.intro.length && this.intro.trim())
+      return false
     let chunk: Chunk | null = this.firstChunk
     while (chunk) {
       if (
@@ -1054,6 +1057,8 @@ export default class MagicString {
       }
       chunk = chunk.next
     }
+    if (this.outro.length && this.outro.trim())
+      return false
     return true
   }
 

test/MagicString.test.ts

@@ -1882,6 +1882,22 @@ describe('magicString', () => {
 
       assert.equal(s.isEmpty(), true)
     })
+
+    it('should count content appended or prepended to the string', () => {
+      assert.equal(new MagicString('').append('X').isEmpty(), false)
+      assert.equal(new MagicString('').prepend('Y').isEmpty(), false)
+
+      const s = new MagicString('abc')
+      s.remove(0, 3)
+      s.append('!')
+      assert.equal(s.toString(), '!')
+      assert.equal(s.isEmpty(), false)
+    })
+
+    it('should still disregard whitespace appended or prepended to the string', () => {
+      const s = new MagicString('').prepend('  ').append('   ')
+      assert.equal(s.isEmpty(), true)
+    })
   })
 
   describe('length', () => {