make sure formatter no longer stack overflows when formatting big lists #5298
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giacomocavalieri
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lpil
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Jan 18, 2026
compiler-core/src/pretty.rs
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| // So in case a `docvec!` starts with a `Vec` we flatten it out to avoid | ||
| // having deeply nested documents. | ||
| match $first.to_doc() { | ||
| first@Document::Vec(_) => first.append(docvec![$($rest.to_doc()),+]), |
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Why not append all the items to the inner vector instead of recursively calling the macro?
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This way we can flatten all vectors at the top of the macro:
docvec![vec1, vec2, a, b] // becomes =>
vec1.append(vec2.append(vec![a, b]))
// Meaning the first two vectors are flattened out, rather than only the first one
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That moves the elements multiples times needlessly, potentially allocating new vectors and copying the existing elements each time. If the Vec is worked with directly it allocates at most once, and moves the new elements once. Is there a reason to do more work to restructure the tree?
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Mhm you're right and just doing it for the first element seems to be fixing the issue anyway. I'll change it to that!
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This PR closes #5297.
This seems to be a really straightforward fix: the
docvec!macro ended up creating deeply nested documentsvec(vec(vec(vec(...), ...), ...), ...). Now if the first item passed to the macro is a vector, it behaves the same as appending to that vector rather than creating a new vector every single time!