Make storage layout specifier accept signed positive expressions

Author: matheusaaguiar

Changelog.md

@@ -2,6 +2,7 @@
 
 Language Features:
 * General: Add a builtin that computes the base slot of a storage namespace using the `erc7201` formula from ERC-7201.
+* Custom Storage Layout: Allow signed positive expressions.
 
 Compiler Features:
 * Commandline Interface: Disallow selecting the deprecated assembly input mode that was only accessible via `--assemble` instead of treating it as equivalent to `--strict-assembly`.

libsolidity/analysis/PostTypeContractLevelChecker.cpp

@@ -181,18 +181,6 @@ void PostTypeContractLevelChecker::checkStorageLayoutSpecifier(ContractDefinitio
 		return;
 	}
 
-	if (!baseSlotExpressionType->isImplicitlyConvertibleTo(*TypeProvider::uint256()))
-	{
-		m_errorReporter.typeError(
-			1481_error,
-			baseSlotExpression.location(),
-			fmt::format(
-				"Base slot expression of type '{}' is not convertible to uint256.",
-				baseSlotExpressionType->humanReadableName()
-			)
-		);
-		return;
-	}
 	storageLayoutSpecifier->annotation().baseSlot = u256(baseSlot);
 
 	bigint size = contractStorageSizeUpperBound(_contract, VariableDeclaration::Location::Unspecified);