test: tests for v-on transform

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

@@ -56,6 +56,9 @@ export function processExpression(
   node: ExpressionNode,
   context: TransformContext
 ) {
+  if (!context.prefixIdentifiers) {
+    return
+  }
   // lazy require dependencies so that they don't end up in rollup's dep graph
   // and thus can be tree-shaken in browser builds.
   const parseScript =
@@ -155,6 +158,9 @@ export function processExpression(
   })
 
   if (children.length) {
+    // mark it empty so that it's more noticeable in case another transform or
+    // codegen forget to handle `.children` first.
+    node.content = __DEV__ ? `[[REMOVED]]` : ``
     node.children = children
   }
 }

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

@@ -1,14 +1,33 @@
 import { DirectiveTransform } from '../transform'
-import { createObjectProperty, createExpression } from '../ast'
+import { createObjectProperty, createExpression, ExpressionNode } from '../ast'
 import { capitalize } from '@vue/shared'
+import { createCompilerError, ErrorCodes } from '../errors'
+import { isSimpleIdentifier } from '../utils'
 
 // v-on without arg is handled directly in ./element.ts due to it affecting
 // codegen for the entire props object. This transform here is only for v-on
 // *with* args.
-export const transformOn: DirectiveTransform = ({ arg, exp, loc }) => {
-  const eventName = arg!.isStatic
-    ? createExpression(`on${capitalize(arg!.content)}`, true, arg!.loc)
-    : createExpression(`'on' + (${arg!.content})`, false, arg!.loc)
+export const transformOn: DirectiveTransform = ({ arg, exp, loc }, context) => {
+  if (!exp) {
+    context.onError(createCompilerError(ErrorCodes.X_V_ON_NO_EXPRESSION, loc))
+  }
+  const { content, children, isStatic, loc: argLoc } = arg!
+  let eventName: ExpressionNode
+  if (isStatic) {
+    // static arg
+    eventName = createExpression(`on${capitalize(content)}`, true, argLoc)
+  } else if (!children) {
+    // dynamic arg with no rewrite
+    eventName = createExpression(
+      `"on" + ${isSimpleIdentifier(content) ? content : `(${content})`}`,
+      false,
+      argLoc
+    )
+  } else {
+    // dynamic arg with ctx prefixing
+    eventName = arg!
+    children.unshift(`"on" + `)
+  }
   // TODO .once modifier handling since it is platform agnostic
   // other modifiers are handled in compiler-dom
   return {