check-magic: Remember all explained magic constants #1294
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Previously, scripts/check-magic would remember only the last explained magic constant, preventing, for example, the explanation of multiple magic constants ahead of a comment block referring to all of them. Moreover, check-magic would only lazily evaluate a provided explanation when actually finding a magic value magic the LHS of the proposed explanation. In particular, a _wrong_ explanation would only be caught if, in the rest of the file under consideration, some matching magic constant would be found. This commit makes check-magic more general so that - it always checks magic value explanations when they are provided, regardless of whether they are needed or not; and, - it remembers all magic values explained so far. Moreover, the `round` function is instrumented to fail if it is called on an odd multiple of 1/2 -- in this case, the rounding is ambiguous (do we want round-half-down or round-half-up?). We also add support for `intdiv(a,b)` to an integer division which we want to assert to be without residue. This can be used instead of `//` to additionally check that the division is indeed integral. Signed-off-by: Hanno Becker <beckphan@amazon.co.uk>
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mkannwischer
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Nov 12, 2025
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LGTM. Thanks @hanno-becker!
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Previously, scripts/check-magic would remember only the last explained magic constant, preventing, for example, the explanation of multiple magic constants ahead of a comment block referring to all of them.
Moreover, check-magic would only lazily evaluate a provided explanation when actually finding a magic value magic the LHS of the proposed explanation. In particular, a wrong explanation would only be caught if, in the rest of the file under consideration, some matching magic constant would be found.
This commit makes check-magic more general so that
Moreover, the
roundfunction is instrumented to fail if it is called on an odd multiple of 1/2 -- in this case, the rounding is ambiguous (do we want round-half-down or round-half-up?).We also add support for
intdiv(a,b)to an integer division which we want to assert to be without residue. This can be used instead of//to additionally check that the division is indeed integral.