fix(vitest): `vi.hoisted` syntax errors on instrumented code

[AriPerkkio]

Description

• Fixes https://github.com/vitest-dev/vitest/issues/6057

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[AriPerkkio]

Current implementation:

import { expect, it, vi } from 'vitest'

let coverageCounter = 0
const nestedHoist = (coverageCounter++, vi.hoisted(() => {
  return 'Nested hoist'
}))

it('nesting vi.hoisted doesnt cause syntax errors', () => {
  expect(nestedHoist).toBe('Nested hoist')
})

becomes:

const { expect, it, vi } = await __vite_ssr_dynamic_import__("/@fs/x/vitest/packages/vitest/dist/index.js")
vi.hoisted(() => {
  return 'Nested hoist'
})

let coverageCounter = 0;
const nestedHoist = (coverageCounter++, );                  // <-- Syntax error
it("nesting vi.hoisted doesnt cause syntax errors", () => {
  expect(nestedHoist).toBe('Nested hoist');
});

I think correct would be

const { expect, it, vi } = await __vite_ssr_dynamic_import__("/@fs/x/vitest/packages/vitest/dist/index.js")
const nestedHoist = vi.hoisted(() => {
  return 'Nested hoist'
})

let coverageCounter = 0;
coverageCounter++;
it("nesting vi.hoisted doesnt cause syntax errors", () => {
  expect(nestedHoist).toBe('Nested hoist');
});

If implementing this via AST modify becomes too difficult I think we could instead add /* istanbul ignore next */ ignore hints in mocking methods before the instrumentation.

[AriPerkkio]

This is getting quite complex. I think better and more maintainable solution is to:

• Prevent @vitest/coverage-istanbul from instrumenting vi.mock|hoisted|etc method calls. This is done by adding /* istanbul ignore next */ ignore hints before detected method calls.
• Throw an error around here if anything else than VariableDeclaration is found, e.g. SequenceExpression

https://github.com/vitest-dev/vitest/blob/073a50c9740f75ba25ec1fabba73b6dae73e66f4/packages/vitest/src/node/hoistMocks.ts#L330

[AriPerkkio]

https://github.com/vitest-dev/vitest/issues/6057#issuecomment-2813403136