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Fix assigning error or event selectors to constant variables. #16325

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Fix assigning error or event selectors to constant variables. #16325

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d9c2c89
Fix constantness of event and error selectors. Reported by https://gi…
rodiazet Dec 3, 2025
d843fe3
Add the changelog entry.
rodiazet Dec 8, 2025
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1 change: 1 addition & 0 deletions Changelog.md
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ Language Features:
Compiler Features:

Bugfixes:
* TypeChecker: Allow assignment of error and event selectors to constant variables.


### 0.8.31 (2025-12-03)
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27 changes: 20 additions & 7 deletions libsolidity/analysis/TypeChecker.cpp
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Expand Up @@ -3280,18 +3280,31 @@ bool TypeChecker::visit(MemberAccess const& _memberAccess)
auto const* functionType = dynamic_cast<FunctionType const*>(exprType);
functionType &&
functionType->hasDeclaration() &&
dynamic_cast<FunctionDefinition const*>(&functionType->declaration()) &&
memberName == "selector"
)
if (auto const* parentAccess = dynamic_cast<MemberAccess const*>(&_memberAccess.expression()))
{
if (dynamic_cast<FunctionDefinition const*>(&functionType->declaration()))
{
bool isPure = *parentAccess->expression().annotation().isPure;
if (auto const* exprInt = dynamic_cast<Identifier const*>(&parentAccess->expression()))
if (exprInt->name() == "this" || exprInt->name() == "super")
isPure = true;
if (auto const* parentAccess = dynamic_cast<MemberAccess const*>(&_memberAccess.expression()))
{
bool isPure = *parentAccess->expression().annotation().isPure;
// Accessing a function selector using `super|this.f.selector`.
if (auto const* exprInt = dynamic_cast<Identifier const*>(&parentAccess->expression()))
if (exprInt->name() == "this" || exprInt->name() == "super")
isPure = true;
Comment on lines +3290 to +3294
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@cameel cameel Dec 8, 2025 •
edited
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This piece of code looked fishy and while poking around it I found another bug with selector constness. I reported it as #16338.

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@cameel cameel Dec 8, 2025 •
edited
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I guess the underlying cause is that the functions themselves are not considered constant, which I also reported as #16339. I'm not sure if we should consider that one a bug though. It might have been intentional, as there are cases where it's straightforward to decide whether a function reference should be const or not as well as some corner cases where it's not so clear.


annotation.isPure = isPure;
annotation.isPure = isPure;
}
}
// In case of event or error definition the selector is always compile-time constant, as it can be
// a keccak256 hash of the event signature or a function selector in case of an error.
else if (
dynamic_cast<EventDefinition const*>(&functionType->declaration()) ||
dynamic_cast<ErrorDefinition const*>(&functionType->declaration())
)
annotation.isPure = true;
}

if (
auto const* varDecl = dynamic_cast<VariableDeclaration const*>(annotation.referencedDeclaration);
!annotation.isPure.set() &&
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20 changes: 20 additions & 0 deletions ...olidity/syntaxTests/types/functionTypes/selector/event_error_selector_pure_assignment.sol
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@@ -0,0 +1,20 @@
event EvExt();
error ErExt();

bytes32 constant eventExtSelectorGlobal = EvExt.selector;
bytes4 constant errorExtSelectorGlobal = ErExt.selector;

contract C {
event Ev();
error Er();

bytes4 constant errorExtSelector = ErExt.selector;
bytes32 constant eventExtSelector = EvExt.selector;

bytes4 constant errorSelector = Er.selector;
bytes32 constant eventSelector = Ev.selector;

bytes4 constant errorSelectorC = C.Er.selector;
bytes32 constant eventSelectorC = C.Ev.selector;
}
// ----