fix(compiler-core): ignore whitespace when matching adjacent v-if (#12321)

close #9173

packages/compiler-core/__tests__/transforms/__snapshots__/vSlot.spec.ts.snap

@@ -246,6 +246,28 @@ return function render(_ctx, _cache) {
 }"
 `;
 
+exports[`compiler: transform component slots > with whitespace: 'preserve' > named slot with v-if + v-else 1`] = `
+"const { resolveComponent: _resolveComponent, withCtx: _withCtx, createSlots: _createSlots, openBlock: _openBlock, createBlock: _createBlock } = Vue
+
+return function render(_ctx, _cache) {
+  const _component_Comp = _resolveComponent("Comp")
+
+  return (_openBlock(), _createBlock(_component_Comp, null, _createSlots({ _: 2 /* DYNAMIC */ }, [
+    ok
+      ? {
+          name: "one",
+          fn: _withCtx(() => ["foo"]),
+          key: "0"
+        }
+      : {
+          name: "two",
+          fn: _withCtx(() => ["baz"]),
+          key: "1"
+        }
+  ]), 1024 /* DYNAMIC_SLOTS */))
+}"
+`;
+
 exports[`compiler: transform component slots > with whitespace: 'preserve' > should not generate whitespace only default slot 1`] = `
 "const { resolveComponent: _resolveComponent, withCtx: _withCtx, openBlock: _openBlock, createBlock: _createBlock } = Vue
 

packages/compiler-core/__tests__/transforms/vSlot.spec.ts

@@ -988,5 +988,19 @@ describe('compiler: transform component slots', () => {
 
       expect(generate(root, { prefixIdentifiers: true }).code).toMatchSnapshot()
     })
+
+    test('named slot with v-if + v-else', () => {
+      const source = `
+        <Comp>
+          <template #one v-if="ok">foo</template>
+          <template #two v-else>baz</template>
+        </Comp>
+      `
+      const { root } = parseWithSlots(source, {
+        whitespace: 'preserve',
+      })
+
+      expect(generate(root, { prefixIdentifiers: true }).code).toMatchSnapshot()
+    })
   })
 })

packages/compiler-core/src/transforms/vSlot.ts

@@ -222,7 +222,7 @@ export function buildSlots(
       let prev
       while (j--) {
         prev = children[j]
-        if (prev.type !== NodeTypes.COMMENT) {
+        if (prev.type !== NodeTypes.COMMENT && isNonWhitespaceContent(prev)) {
           break
         }
       }