fix: trim replacements longer than the range they replace (#312)

Author: sarathfrancis90

src/Chunk.ts

@@ -164,11 +164,14 @@ export default class Chunk {
 
     if (trimmed.length) {
       if (trimmed !== this.content) {
-        this.split(this.start + trimmed.length).edit('', undefined, true)
         if (this.edited) {
-          // save the change, if it has been edited
+          // the content of an edited chunk no longer lines up with its range in the
+          // original string, so there is no index to split at - trim it in place
           this.edit(trimmed, this.storeName, true)
         }
+        else {
+          this.split(this.start + trimmed.length).edit('', undefined, true)
+        }
       }
       return true
     }
@@ -190,12 +193,15 @@ export default class Chunk {
 
     if (trimmed.length) {
       if (trimmed !== this.content) {
-        const newChunk = this.split(this.end - trimmed.length)
         if (this.edited) {
-          // save the change, if it has been edited
-          newChunk.edit(trimmed, this.storeName, true)
+          // the content of an edited chunk no longer lines up with its range in the
+          // original string, so there is no index to split at - trim it in place
+          this.edit(trimmed, this.storeName, true)
+        }
+        else {
+          this.split(this.end - trimmed.length)
+          this.edit('', undefined, true)
         }
-        this.edit('', undefined, true)
       }
       return true
     }

test/MagicString.test.ts

@@ -1675,6 +1675,31 @@ describe('magicString', () => {
       assert.equal(s.toString(), 'abcd')
     })
 
+    it('should trim a replacement that is longer than the range it replaces', () => {
+      const s = new MagicString('ab')
+      s.overwrite(0, 1, '   xyz')
+      s.trimStart()
+
+      assert.equal(s.toString(), 'xyzb')
+
+      for (const line of s.generateDecodedMap({ source: 'in.js' }).mappings) {
+        for (const segment of line) {
+          if (segment.length > 1) {
+            assert.ok(segment[1]! >= 0 && segment[2]! >= 0 && segment[3]! >= 0, `segment ${JSON.stringify(segment)} points outside the original`)
+          }
+        }
+      }
+    })
+
+    it('should trim the end of a replacement that is longer than the range it replaces', () => {
+      const s = new MagicString('ab')
+      s.overwrite(1, 2, 'xyz   ')
+      s.trimEnd()
+
+      assert.equal(s.toString(), 'axyz')
+      assert.equal(s.slice(0, 2), 'axyz')
+    })
+
     it('should trim original content before replaced content', () => {
       const s = new MagicString('abc   def')