Vue2.7 defineEmits/defineProps compile error about vue

[DeAntiWang]

Aah I see! Given that Vitest manages to pull off the coverage on Vue components, this might be a misconfiguration: Istanbul should maybe instrument the code after and use source maps to refer to the original place

oh cool! thanks, I'll have a look.
but there are many complex reasons leading us to choose the way to instrument the code first.

Supporting SuequenceExpression for @vue/compile-sfc seems like a nice thing too. Maybe I'll try to make a PullRequest for that.

[DeAntiWang]

have submitted a PullRequest(#13124) about this

[posva]

How did you find this problem? I don’t see why one would write a sequence when defining the emit function?

[DeAntiWang]

How did you find this problem? I don’t see why one would write a sequence when defining the emit function?

Because of istanbuljs's instrumentation process. The VariableDeclaration code after instrumenting will be compiled to SequenceExpression.

Like this code:

<script setup>
const emits = defineEmits(['input']);
</script>

after intrument, it will become like this:

<script setup>
// some unrelated report init code
const emits = (report(0), defineEmits(['input']));
</script>

[posva]

Aah I see! Given that Vitest manages to pull off the coverage on Vue components, this might be a misconfiguration: Istanbul should maybe instrument the code after and use source maps to refer to the original place

[yyx990803]

I'm not convinced that this complexity should be dealt with in Vue - instrumenting raw SFC code just sounds wrong. Only handling sequences also seems like an incomplete fix, as there are other cases where the macros won't be compiled. For example, what if the instrumentation wraps the defineXXX macros in conditional branches?

Even just for sequences, the PR also has even more edge cases:

• It assumes the defineXXX always is the last in the sequence, so it would fail for

  const props = (Date.now(), defineProps(['input']), Date.now())

• In the multi-declaration case, it also doesn't account for duplicated placeholders:

  const foo = 1, props = (Date.now(), defineProps(['input']))
  const bar = 1, emits = (Date.now(), defineEmits(['input']))

  Generated code will error because two variables named _ are declared.

In principle, compileScript expects to work with the exact code written by the developer, so we do not account for extremely unlikely usage like sequence expressions. But if the goal is to make the logic robust enough that it can handle unknown instrumentation by other tools, then the complexity will explode and I don't think Vue should be responsible for that.