Add support for subsequent zones

Closes GH-4.

Reviewed-by: Titus Wormer <tituswormer@gmail.com>

lib/index.js

@@ -88,28 +88,35 @@ export function zone(node, name, handler) {
             {start, end: index, parent: scope}
           )
 
-          if (nodes) {
-            // Ensure no empty nodes are inserted.
-            // This could be the case if `end` is in `nodes` but no `end` node exists.
-            /** @type {Array<Nodes>} */
-            const result = []
-            let offset = -1
+          if (!nodes) {
+            marker = undefined
+            scope = undefined
+            return
+          }
 
-            while (++offset < nodes.length) {
-              const node = nodes[offset]
-              if (node) result.push(node)
-            }
+          // Ensure no empty nodes are inserted.
+          // This could be the case if `end` is in `nodes` but no `end` node exists.
+          /** @type {Array<Nodes>} */
+          const result = []
+          let offset = -1
 
-            scope.children.splice(
-              start,
-              index - start + 1,
-              // @ts-expect-error: Assume the correct children are passed.
-              ...result
-            )
+          while (++offset < nodes.length) {
+            const node = nodes[offset]
+            if (node) result.push(node)
           }
 
+          const deleteCount = index - start + 1
+          scope.children.splice(
+            start,
+            deleteCount,
+            // @ts-expect-error: Assume the correct children are passed.
+            ...result
+          )
+
           marker = undefined
           scope = undefined
+
+          return index - deleteCount + result.length
         }
       }
     }

test/fixtures/remove-subsequent/index.js

@@ -0,0 +1,14 @@
+/**
+ * @typedef {import('mdast').Root} Root
+ */
+
+import {zone} from 'mdast-zone'
+
+/**
+ * @param {Root} tree
+ */
+export default function assertion(tree) {
+  zone(tree, 'foo', function () {
+    return []
+  })
+}

test/fixtures/remove-subsequent/input.md

@@ -0,0 +1,19 @@
+# Foo
+
+<!--foo start-->
+
+Foo.
+
+Foo.
+
+<!--foo end-->
+
+Bar.
+
+<!--foo start-->
+
+Foo.
+
+Foo.
+
+<!--foo end-->

test/fixtures/remove-subsequent/output.md

@@ -0,0 +1,3 @@
+# Foo
+
+Bar.

test/fixtures/replace-subsequent/index.js

@@ -0,0 +1,19 @@
+/**
+ * @typedef {import('mdast').Root} Root
+ */
+
+import {zone} from 'mdast-zone'
+
+/**
+ * @param {Root} tree
+ */
+export default function assertion(tree) {
+  zone(tree, 'foo', function () {
+    return [
+      {
+        type: 'paragraph',
+        children: [{type: 'text', value: 'Bar.'}]
+      }
+    ]
+  })
+}

test/fixtures/replace-subsequent/input.md

@@ -0,0 +1,15 @@
+# Foo
+
+<!--foo start-->
+
+Foo.
+
+<!--foo end-->
+
+Bar.
+
+<!--foo start-->
+
+Foo.
+
+<!--foo end-->

test/fixtures/replace-subsequent/output.md

@@ -0,0 +1,7 @@
+# Foo
+
+Bar.
+
+Bar.
+
+Bar.