Fix calldatasize check for fallback#478
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The previous attempt kept the instance head polymorphic in args/rets while the body called `fn(())`, which forces args = (). The typechecker rejected this as 'type not polymorphic enough'. Specialise the head to Fallback(payability, (), (), fn) so the declared and inferred signatures match. The ABIAttribs / ABIDecode / ABIEncode constraints are dropped since the body no longer decodes or encodes anything, and ContractDispatch.hs already builds the Fallback value with Proxy(()) for args and rets (sigParams is empty and sigReturn defaults to unit), so instance resolution still succeeds at the dispatch call site. Co-authored-by: Alex Beregszaszi <alex@rtfs.hu>
axic
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Jun 19, 2026
| cdsz := calldatasize() | ||
| } | ||
| if ((cdsz - 4) < hdsz) { | ||
| if (cdsz < (hdsz + 4)) { |
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The original code her resulted in underflow (wraparound), which "kind of" made the flow work.
The problem is that if this gets fixed here, then the do_exec() chain ends up in both cases (cdsz < 4 and cdsz >= 4) in the variant where cdsz < 4 is checked (the check-decode-exec-encode variant).
I fixed this with specializing the fallback case to not reuse that code.
This then showed yet another issue: without the implicit stop/return(0,0), we end up with main function's return:
mstore(0, _mainresult)
return(0, 32)
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