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Update when we can infer void from a function body #468

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lucacasonato opened this issue May 13, 2024 · 3 comments · Fixed by #470
Closed

Update when we can infer void from a function body #468

lucacasonato opened this issue May 13, 2024 · 3 comments · Fixed by #470
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bug Something isn't working fast check

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@lucacasonato
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lucacasonato commented May 13, 2024 •
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Right now we sometimes incorrectly infer the function return type due to our return statement analysis. The only cases where we can safely infer void is when:

  • we are in a function declaration, there are no returns with value
  • or when we are in a function expression or arrow function expression and either:
    • a single return statement without value is anywhere in the body
    • the body is empty

Notably, we can not infer a function expression from expressions such as () => { n() }, because the return type may be never if n() returns never.

Sync functions: https://www.typescriptlang.org/play/?#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXxAA8sMAKASgC55UQA3EGAbgCgWiAHHGDJNTXPigV4AbxbxJBYmXKsAvm07deKdNjzwARiPFT4cDMhioWi9oS48 6wfDC6JUrInikA5hBxaoEACoAFlgAzuRiTvqSRCQUrPqK obGpubK1moCmsCO mZKlir2eMG8CAC8bmFlAHzh tGyCvlWvGDFqvAVIjV1UkkmeRYtRagl8O6dlZ21es6uHl4 -kGhvZHSMXIR8Al9IEYDqQXWbaO8AZPdM9uDaa3t8FiTGRqoOVINsbfH92fwAFbPfivd6SfopZqFU5jADWQNseFBj3mnm8vkCITCs3Wny28W24O w2hvAg8MybyxN3kQA
Async functions: https://www.typescriptlang.org/play/?#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXxAA8sMAKASgC55UQA3EGAbgCgWiAHHGDeKAZwCe6JGky58UCvADeLeAoLEy5VgF82nbrwHCwo9NjzwARtLmL4cDMhioWG9oS48 QkSkMT4Yc-MVYiPCkAOYQOCZQEAAqABZY-OSy-pYKRCQUrJYalta29o5arroeYkb4wH6WDprO2j54-LwIALxuesFJLQB8yZbpKuq1LrxgjbxBbSX60j19inl2NU4jDahN8CHwU 4zXb0WAUGh4ZEx8YnzqUoZqinwOQsgNkuFda5j67yx2 0iswd7ssiqNxvAsL9pgZxHgqooBplge9QV94AArSG7aHlOEKRYFYb1T4bADWmI6nhhqFx4OOYQiUTiCSSh2uCLu2Xu KRq2JvAg5NKXlhLLYaiAA
@lucacasonato lucacasonato added fast check bug Something isn't working labels May 13, 2024
@lucacasonato
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And classes and object literals: https://www.typescriptlang.org/play/?#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXxAA8sMAKASgC55UQA3EGAbgCg2iAHHGDeSKAM4D4AQXgBvFvGnwoFCVJlKiJCqyUBfRdO3wARvMlKlcDMhipdWrS07deYPAN4AheAF4FSueS-HpKmTk6jIaADRsSga Rv7wpuaWmiw2djx8TrwAwh7S-EJ 0j6FxoFqVpEy0SUmIGYWFRpAA

@marvinhagemeister
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For completeness: This requires to traverse into every block-like scope to potentially find return types:

export function foo() {
  for (let i = 0; i < 10; i  ) {
    if (i === 10) {
      return 42
    }
  }
}

@lucacasonato
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We already do that 👍

@lucacasonato lucacasonato mentioned this issue May 13, 2024
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fix: handle return statements in functions correctly denoland/deno_graph
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@marvinhagemeister @lucacasonato