[haybinalim]

What I did

Web3.solidity_keccak now right-pads a standalone bytesN value that is shorter than N bytes to N bytes, the same way Solidity's abi.encodePacked and eth_abi.packed.encode_packed encode it. Before this change, solidity_keccak(["bytes2"], [b"a"]) hashed 0x61 instead of 0x6100. Since #3882, validate_abi_value accepts these short values, so they passed validation and gave a hash that differs from Solidity.

Closes #3906

How I did it

• hex_encode_abi_type (web3/_utils/encoding.py): for a standalone bytesN (no force_size), right-pad the hex value with zero bytes to N bytes. Dynamic bytes is unchanged.
• Values longer than N bytes still raise Web3TypeError. validate_abi_value already rejects them (since fix: reject out-of-range integers and junk hex in validate_abi_value #3882), before the encoder runs, and this PR keeps that. I did not truncate them, because there's no single right way to do it: Solidity won't implicitly convert a longer value to bytesN, an explicit bytesN(x) keeps the leftmost bytes, and eth_abi's encode_packed raises ValueOutOfBounds. Hashing a cut-down value without warning would bring back the same kind of mismatch this PR fixes. The new tests cover this.
• bytesN array elements are left alone. Fix solidity_keccak for bytesN array elements #3886 fixes those (they have to be padded to 32 bytes) in the same branch of hex_encode_abi_type. This change only touches the force_size is None path, so the two PRs don't overlap in behavior. Whichever one lands second is a one-line rebase (an if force_size is not None / elif abi_type != "bytes" pair), and I'm happy to do it.
• Updated the existing ["bytes3"], ["0x5402"] case in test_solidity_keccak. It expected the same hash as bytes2(0x5402), but Solidity hashes bytes3(0x540200) to 0xed37fb74…. I also updated the hex_encode_abi_type unit case for bytes3 (0x5402 → 0x540200).
• Documented the padding and the longer-value error in Web3.solidity_keccak (docs/web3.main.rst), with a bytes4(hex"1234") example.

There's no newsfragment because the repo now uses GitHub-generated release notes, per the contributing guide.

Note: #3907 and #3911 also target #3906, but they produce different hashes from Solidity for bytes2(b"a"). #3907 pads to 32 bytes (0x294587bf…), and #3911 left-pads and encodes hex strings as UTF-8 (0x97222015…). Solidity gives 0xa3fe1181…. #3911 also includes unrelated Wei/Gwei changes.

How to verify it

from web3 import Web3
from eth_abi.packed import encode_packed

Web3.solidity_keccak(["bytes2"], [b"a"]) == Web3.keccak(encode_packed(["bytes2"], [b"a"]))  # True now
Web3.solidity_keccak(["bytes4"], ["0x1234"]).to_0x_hex()
# '0x83cdd5d8e9eedfbb36b0f6748705833df28b0a094f672873aea9e21eda67aed9'
Web3.solidity_keccak(["bytes2"], ["0x010203"])  # Web3TypeError, unchanged

I took every new expected hash from keccak256(abi.encodePacked(...)) in a contract compiled with solc 0.8.26 and called on py-evm (EthereumTesterProvider). Each one also matches keccak(eth_abi.packed.encode_packed(...)):

types	values	hash (Solidity = eth_abi = this PR)
bytes2	b"a" / "0x61"	0xa3fe1181…
bytes3	"0x5402"	0xed37fb74…
bytes4	"0x1234"	0x83cdd5d8…
bytes32	"0x01"	0x48078cfe…
bytes4, bytes1	b"\x01\x02", b"\x03"	0x84afedaa…
string, bool, uint16, bytes4, address	"testing a string!", False, 299, "0x5402", 0x49Ed…5614	0x9f22f3fb…

Local runs (Python 3.12):

• pytest tests/core/utilities (604 passed) and pytest tests/core/web3-module (all passed)
• pytest tests/integration/test_ethereum_tester.py -k "solidity_keccak or Web3Module": 42 passed, 1 skipped (batch requests, as on main)
• The new and updated cases fail on main (10 failures) and pass with this change
• ruff check ., ruff format --check . and mdformat --check *.md pass. mypy -p web3 -p ens reports nothing in the touched files.

Checklist

• All changes are completed
• Change is covered in tests
• Documentation is complete