fix: allow keccak256() and uint() in compile-time context for layout base expressions

[JPier34]

Summary

Implements evaluation of keccak256() and explicit uint() conversion in a compile-time context. This allows using keccak256() in storage layout base expressions:

contract C layout at uint(keccak256("my.contract.id")) {}

Fixes #16421. Implements Stage 1 of #16420.

Motivation

Layout base expressions commonly use either ERC-7201 (handled in PR #15968) or plain hashing with keccak256(). This change supports the latter. Since keccak256() returns bytes32 while the layout base must be an integer, we also evaluate explicit uint() conversions at compile time so that uint(keccak256("...")) is valid.

Changes

• ConstantEvaluator.cpp/h

  • Evaluate uint(...) type conversion at compile time when the target type is uint256.
  • Evaluate builtin keccak256(...) at compile time when the argument is a string or hex literal.

• Tests

  • literal_cast.sol now expects success for uint(42).
  • New test layout_keccak256_string_literal.sol for layout at uint(keccak256("...")).

Backwards compatibility

Fully backwards-compatible; no change to runtime behaviour.

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[Copilot]

Pull request overview

This PR implements compile-time evaluation of keccak256() and explicit uint() type conversions, enabling storage layout base expressions like contract C layout at uint(keccak256("my.contract.id")) {}. This addresses issue #16421 and implements Stage 1 of issue #16420.

Changes:

• Adds compile-time evaluation support for uint256 type conversions from rational values
• Adds compile-time evaluation support for keccak256() with string and hex string literals
• Updates test expectations to reflect the new compile-time capabilities

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
libsolidity/analysis/ConstantEvaluator.h	Adds endVisit method declaration for FunctionCall nodes
libsolidity/analysis/ConstantEvaluator.cpp	Implements compile-time evaluation logic for uint() conversions and keccak256() calls, with proper range checking and error handling
test/libsolidity/syntaxTests/storageLayoutSpecifier/literal_cast.sol	Removes error expectation since uint(42) is now supported in compile-time context
test/libsolidity/syntaxTests/storageLayoutSpecifier/layout_keccak256_string_literal.sol	Adds new test case demonstrating the main use case: uint(keccak256("...")) in layout expressions

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