fix(compiler-core): adjacent v-else should cause a compiler error

Author: linzhe141

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

@@ -301,6 +301,25 @@ describe('compiler: v-if', () => {
       ])
     })
 
+    test('error on adjacent v-else', () => {
+      const onError = vi.fn()
+
+      const {
+        node: { branches },
+      } = parseWithIfTransform(
+        `<div v-if="false"/><div v-else/><div v-else/>`,
+        { onError },
+        0,
+      )
+
+      expect(onError.mock.calls[0]).toMatchObject([
+        {
+          code: ErrorCodes.X_V_ELSE_NO_ADJACENT_IF,
+          loc: branches[branches.length - 1].loc,
+        },
+      ])
+    })
+
     test('error on user key', () => {
       const onError = vi.fn()
       // dynamic

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

@@ -150,6 +150,15 @@ export function processIf(
             createCompilerError(ErrorCodes.X_V_ELSE_NO_ADJACENT_IF, node.loc),
           )
         }
+        // Check that there should not be two adjacent v-else
+        if (
+          dir.name === 'else' &&
+          sibling.branches[sibling.branches.length - 1].condition === undefined
+        ) {
+          context.onError(
+            createCompilerError(ErrorCodes.X_V_ELSE_NO_ADJACENT_IF, node.loc),
+          )
+        }
 
         // move the node to the if node's branches
         context.removeNode()