We were trapping the host context in case a sub call was exhausting the
storage deposit limit set for this sub call. This prevents the caller
from handling this error. In this PR we added a new error code that is
returned when either gas or storage deposit limit is exhausted by the
sub call.

We also remove the longer used `NotCallable` error. No longer used
because this is no longer an error: It will just be a balance transfer.

We also make `set_code_hash` infallible to be consistent with other host
functions which just trap on any error condition.

---------

Co-authored-by: GitHub Action <action@github.com>

* Add a bunch of differential tests to ensure that responses from
eth-rpc matches the one from `geth`
- These
[tests](https://github.com/paritytech/polkadot-sdk/blob/pg/fix-geth-diff/substrate/frame/revive/rpc/examples/js/src/geth-diff.test.ts)
are not run in CI for now but can be run locally with
```bash
cd revive/rpc/examples/js
bun test
```

* EVM RPC server will not fail gas_estimation if no gas is specified, I
updated pallet-revive to add an extra `skip_transfer` boolean check to
replicate this behavior in our pallet

* `eth_transact` and `bare_eth_transact` api have been updated to use
`GenericTransaction` directly as this is what is used by
`eth_estimateGas` and `eth_call`

## TODO

- [ ]  Add tests the new `skip_transfer` flag

---------

Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: Alexander Theißen <alex.theissen@me.com>

Enhance the `delegate_call` function to accept an `address` target
parameter instead of a `code_hash`. This allows direct identification of
the target contract using the provided address.
Additionally, introduce parameters for specifying a customizable
`ref_time` limit and `proof_size` limit, thereby improving flexibility
and control during contract interactions.

---------

Co-authored-by: Alexander Theißen <alex.theissen@me.com>

This PR update the pallet to use the EVM 18 decimal balance in contracts
call and host functions instead of the native balance.

It also updates the js example to add the piggy-bank solidity contract
that expose the problem

---------

Co-authored-by: GitHub Action <action@github.com>

This PR removes the `transfer` syscall and changes balance transfers to
make the existential deposit (ED) fully transparent for contracts.

The `transfer` API is removed since there is no corresponding EVM opcode
and transferring via a call introduces barely any overhead.

We make the ED transparent to contracts by transferring the ED from the
call origin to nonexistent accounts. Without this change, transfers to
nonexistant accounts will transfer the supplied value minus the ED from
the contracts viewpoint, and consequentially fail if the supplied value
lies below the ED. Changing this behavior removes the need for contract
code to handle this rather annoying corner case and aligns better with
the EVM. The EVM charges a similar deposit from the gas meter, so
transferring the ED from the call origin is practically the same as the
call origin pays for gas.

---------

Signed-off-by: xermicus <cyrill@parity.io>
Signed-off-by: Cyrill Leutwiler <bigcyrill@hotma...>

Various fixes for the release of eth-rpc & ah-westend-runtime

- Bump asset-hub westend spec version
- Fix the status of the Receipt to properly report failed transactions
- Fix value conversion between native and eth decimal representation

---------

Co-authored-by: GitHub Action <action@github.com>

Since https://github.com/paritytech/polkadot-sdk/pull/6266 we no longer
require a custom toolchain to build the `pallet-revive-fixtures`. Hence
we no longer have to guard the build behind a feature flag.

---------

Co-authored-by: GitHub Action <action@github.com>

- Bound T::Hash to H256
- Implement the block hash API

---------

Signed-off-by: xermicus <cyrill@parity.io>
Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Co-authored-by: command-bot <>
Co-authored-by: GitHub Action <action@github.com>

This PR implements the contract API to query the code size of a given
address.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Signed-off-by: xermicus <cyrill@parity.io>
Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: command-bot <>
Co-authored-by: PG Herveou <pgherveou@gmail.com>

Implement a syscall to retreive the transaction origin.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Signed-off-by: xermicus <cyrill@parity.io>
Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: command-bot <>
Co-authored-by: Alexander Theißen <alex.theissen@me.com>

Fixes #5576

This allows contracts to be used with an AccountId32 through normal
extrinsics and not only through the eth compat layer. It works by adding
a new extrinsic `map_account` that lets people register their
AccountId32.

---------

Co-authored-by: command-bot <>
Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: Cyrill Leutwiler <cyrill@parity.io>

This PR introduces the necessary changes to pallet-revive for
integrating with our Ethereum JSON-RPC.
The RPC proxy itself will be added in a follow up.

## Changes

- A new pallet::call `Call::eth_transact`. This is used as a wrapper to
accept unsigned Ethereum transaction, valid call will be routed to
`Call::call` or `Call::instantiate_with_code`

- A custom UncheckedExtrinsic struct, that wraps the generic one usually
and add the ability to check eth_transact calls sent from an Ethereum
JSON-RPC proxy.
- Generated types and traits to support implementing a JSON-RPC Ethereum
proxy.

## Flow Overview:
- A user submits a transaction via MetaMask or another
Ethereum-compatible wallet.
- The proxy dry run the transaction and add metadata to the call (gas
limit in Weight, storage deposit limit, and length of bytecode and
constructor input for contract instantiation)
- The raw transaction, along with the additional metadata, is submitted
to the node as an unsigned e...

# Description
Update `ext_code_hash` to match
[EIP-1052](https://eips.ethereum.org/EIPS/eip-1052) specs. Since all
possible results are written into output pointer then there's no need
for a return value.

https://github.com/paritytech/revive/pull/77

Failed call frames do not produce new return data but still reset it.

---------

Signed-off-by: xermicus <cyrill@parity.io>
Co-authored-by: GitHub Action <action@github.com>

This PR introduces the concept of immutable storage data, used for
[Solidity immutable
variables](https://docs.soliditylang.org/en/latest/contracts.html#immutable).

This is a minimal implementation. Immutable data is attached to a
contract; to keep `ContractInfo` fixed in size, we only store the length
there, and store the immutable data in a dedicated storage map instead.
Which comes at the cost of requiring an additional storage read (costly)
for contracts using this feature.

We discussed more optimal solutions not requiring any additional storage
accesses internally, but they turned out to be non-trivial to implement.
Another optimization benefiting multiple calls to the same contract in a
single call stack would be to cache the immutable data in `Stack`.
However, this potential creates a DOS vulnerability (the attack vector
is to call into as many contracts in a single stack as possible, where
they all have maximum immutable data to fill the cache as efficiently as
possible). So this either has to be guaranteed to be a non-issue by
limits, or, more likely, to have some logic to bound the cache.
Eventually, we should think about introducing the concept of warm and
cold storage reads (akin to EVM). Since immutable variables are commonly
used in contracts, this change is blocking our initial launch and we
should only optimize it properly in follow-ups.

This PR also disables the `set_code_hash` API (which isn't usable for
Solidity contracts without pre-compiles anyways). With immutable storage
attached to contracts, we now want to run the constructor of the new
code hash to collect the immutable data during `set_code_hash`. This
will be implemented in a follow up PR.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Signed-off-by: xermicus <cyrill@parity.io>
Co-authored-by: command-bot <>
Co-authored-by: Alexander Theißen <alex.theissen@me.com>
Co-authored-by: PG Herveou <pgherveou@gmail.com>

This PR introduces 2 new syscalls: `return_data_size` and
`return_data_copy`, resembling the semantics of the EVM `RETURNDATASIZE`
and `RETURNDATACOPY` opcodes.

The ownership of `ExecReturnValue` (the return data) has moved to the
`Frame`. This allows implementing the new contract API functionality in
ext with no additional copies. Returned data is passed via contract
memory, memory is (will be) metered, hence the amount of returned data
can not be statically known, so we should avoid storing copies of the
returned data if we can. By moving the ownership of the exectuables
return value into the `Frame` struct we achieve this.

A zero-copy implementation of those APIs would be technically possible
without that internal change by making the callsite in the runtime
responsible for moving the returned data into the frame after any call.
However, resetting the stored output needs to be handled in ext, since
plain transfers will _not_ affect the stored return data (and we don't
want to handle this special call case inside the `runtime` API). This
has drawbacks:
- It can not be tested easily in the mock.
- It introduces an inconsistency where resetting the stored output is
handled in ext, but the runtime API is responsible to store it back
correctly after any calls made. Instead, with ownership of the data in
`Frame`, both can be handled in a single place. Handling both in `fn
run()` is more natural and leaves less room for runtime API bugs.

The returned output is reset each time _before_ running any executable
in a nested stack. This change should not incur any overhead to the
overall memory usage as _only_ the returned data from the last executed
frame will be kept around at any time.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Signed-off-by: xermicus <cyrill@parity.io>
Co-authored-by: command-bot <>
Co-authored-by: PG Herveou <pgherveou@gmail.com>

This was necessary when we needed to compact encode a
`Option<T::Balance>` which is no longer necessary. The storage deposit
limit is now non optional. This is just a left over.

Also got rid of the `T::Hash: IsType<H256>`. We use `keccak256` instead
of the generic hash function everywhere now.

This adds an API method `balance_of`, corresponding to the
[BALANCE](https://www.evm.codes/#31?fork=cancun) EVM opcode.

In `Ext`, `balance` and `balance_of` are internally routed through the
same new `account_balance` method: `balance` is technically the same as
`balance_of` with the caller address. This avoids duplicating all the
tests and avoids a small inefficiency (in theory, `balance` directly
call `balance_of` however this introduces a round trip of converting the
target address to a H160 and back).

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Signed-off-by: xermicus <cyrill@parity.io>
Co-authored-by: command-bot <>

Fixes #5577 

I decided to bubble up the error from where we actually try to load the
contract info. This helps to make sure that we don't miss some entry
point by accident. The draw back is that we have to live with some
additional `.expect`.

@pgherveou

 With this logic the proxy and its runtime part should be
completely unaware whether something is a contract call or a balance
transfer. They should just route everything into pallet_revive.

---------

Co-authored-by: Cyrill Leutwiler <cyrill@parity.io>

Fix https://github.com/paritytech/polkadot-sdk/issues/5629

fix #5574

- Use U256 instead of BalanceOf<T> and MomentOf<T> in Ext trait
- Enforce H256 for T::Hash

The Ext trait still depends on the associated type `T: Config`, we can
look into refactoring it even more later but even in the current state
it should not influence how the data is encoded / decoded between the
contract and the host
```
fn caller(&self) -> Origin<Self::T>;
-> only use to extract the address of the caller 

fn account_id(&self) -> &AccountIdOf<Self::T>;
 -> only used to expose the address or access the account_id internally   

fn gas_meter(&self) -> &GasMeter<Self::T>;
fn gas_meter_mut(&mut self) -> &mut GasMeter<Self::T>;
 -> encoding does not depend on T

fn call_runtime(&self, call: <Self::T as Config>::RuntimeCall) -> DispatchResultWithPostInfo;
-> Substrate specific, just an opaque blob of bytes from the contract's perspective

fn contract_info(&mut self) -> &mut ContractInfo<Self::T>;
fn transient_storage(&mut self) -> &mut TransientStorage<Self::T>;
-> gated by #[cfg(any(test, feature = "runtime-benchmarks"))]
```

---------

Co-authored-by: Alexander Theißen <alex.theissen@me.com>

Before we only supported CREATE2 semantics for contract address
derivations. In order to be compatible we also want to allow CREATE1
semantics. We accomplish this to make the salt an `Option` in all places
where it is used. Supplying `None` will use CREATE1 semantics by just
using the deployers account nonce.

## Todo
- [x] Add new tests specific for CREATE1

Co-authored-by: Alexander Theißen <alex.theissen@me.com>
Co-authored-by: command-bot <>

This is a heavily modified and stripped down version of
`pallet_contracts`. We decided to fork instead of extend the old pallet.
Reasons for that are:

- There is no benefit of supporting both on the same pallet as the
intended payload for the new pallet (recompiled YUL) will be using a
different ABI.
- It is much easier since it allows us to remove all the code that was
necessary to support Wasm and focus fully on running cross compiled YUL
contracts.

**The code is reviewable but can't be merged because it depends on an
unreleased version of PolkaVM via git.**

## Current state

All tests are passing and the code is not quick and dirty but written to
last. The work is not finished, though. It is included in the
`kitchensink-runtime` and a node can be built. However, we merge early
in order to be able to start testing other components as early as
possible.

Outstanding changes are tracked here and will be merged separately:
https://github.com/paritytech/polk...

Introduce transient storage, which behaves identically to regular
storage but is kept only in memory and discarded after every
transaction. This functionality is similar to the `TSTORE` and `TLOAD`
operations used in Ethereum.

The following new host functions have been introduced:
`get_transient_storage`
`set_transient_storage`
`take_transient_storage`
`clear_transient_storage`
`contains_transient_storage`
Note: These functions are declared as `unstable` and thus are not
activated.

---------

Co-authored-by: command-bot <>
Co-authored-by: PG Herveou <pgherveou@gmail.com>
Co-authored-by: Alexander Theißen <alex.theissen@me.com>

This should remove nearly all usage of `sp-std` except:
- bridge and bridge-hubs
- a few of frames re-export `sp-std`, keep them for now
- there is a usage of `sp_std::Writer`, I don't have an idea how to move
it

Please review proc-macro carefully. I'm not sure I'm doing it the right
way.

Note: need `/bot fmt`

---------

Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: command-bot <>

This PR implements the `READ_ONLY` flag to be used as a `Callflag` in
the `call` function.
The flag indicates that the callee is restricted from modifying the
state during call execution.
It is equivalent to Ethereum's
[STATICCALL](https://eips.ethereum.org/EIPS/eip-214).

---------

Co-authored-by: command-bot <>
Co-authored-by: Andrew Jones <ascjones@gmail.com>
Co-authored-by: Alexander Theißen <alex.theissen@me.com>

fix https://github.com/paritytech/polkadot-sdk/issues/4163

This PR does the following:
Update to pallet-contracts-proc-macro: 
- Parse #[cfg] so we can add a dummy noop host function for benchmark.
- Generate BenchEnv::<host_fn> so we can call host functions directly in
the benchmark.
- Add the weight of the noop host function before calling the host
function itself

Update benchmarks:
- Update all host function benchmark, a host function benchmark now
simply call the host function, instead of invoking the function n times
from within a contract.
- Refactor RuntimeCosts & Schedule, for most host functions, we can now
use the generated weight function directly instead of computing the diff
with the cost! macro

```rust
// Before
#[benchmark(pov_mode = Measured)]
fn seal_input(r: Linear<0, API_BENCHMARK_RUNS>) {
    let code = WasmModule::<T>::from(ModuleDefinition {
        memory: Some(ImportedMemory::max::<T>()),
        imported_functions: vec![ImportedFunction {
            module: "seal0",
            name: "seal_input",
            params: vec![ValueType::I32, ValueType::I32],
            return_type: None,
        }],
        data_segments: vec![DataSegment { offset: 0, value: 0u32.to_le_bytes().to_vec() }],
        call_body: Some(body::repeated(
            r,
            &[
                Instruction::I32Const(4), // ptr where to store output
                Instruction::I32Const(0), // ptr to length
                Instruction::Call(0),
            ],
        )),
        ..Default::default()
    });

    call_builder!(func, code);

    let res;
    #[block]
    {
        res = func.call();
    }
    assert_eq!(res.did_revert(), false);
}
```

```rust
// After
fn seal_input(n: Linear<0, { code::max_pages::<T>() * 64 * 1024 - 4 }>) {
    let mut setup = CallSetup::<T>::default();
    let (mut ext, _) = setup.ext();
    let mut runtime = crate::wasm::Runtime::new(&mut ext, vec![42u8; n as usize]);
    let mut memory = memory!(n.to_le_bytes(), vec![0u8; n as usize],);
    let result;
    #[block]
    {
        result = BenchEnv::seal0_input(&mut runtime, &mut memory, 4, 0)
    }
    assert_ok!(result);
    assert_eq!(&memory[4..], &vec![42u8; n as usize]);
}
``` 

[Weights
compare](https://weights.tasty.limo/compare?unit=weight&ignore_errors=true&threshold=10&method=asymptotic&repo=polkadot-sdk&old=master&new=pg%2Frework-host-benchs&path_pattern=substrate%2Fframe%2Fcontracts%2Fsrc%2Fweights.rs%2Cpolkadot%2Fruntime%2F*%2Fsrc%2Fweights%2F**%2F*.rs%2Cpolkadot%2Fbridges%2Fmodules%2F*%2Fsrc%2Fweights.rs%2Ccumulus%2F**%2Fweights%2F*.rs%2Ccumulus%2F**%2Fweights%2Fxcm%2F*.rs%2Ccumulus%2F**%2Fsrc%2Fweights.rs)

---------

Co-authored-by: command-bot <>
Co-authored-by: Alexander Theißen <alex.theissen@me.com>

[Weights
compare](https://weights.tasty.limo/compare?unit=weight&ignore_errors=true&threshold=10&method=asymptotic&repo=polkadot-sdk&old=master&new=pg%2Fbench_tweaks&path_pattern=substrate%2Fframe%2F**%2Fsrc%2Fweights.rs%2Cpolkadot%2Fruntime%2F*%2Fsrc%2Fweights%2F**%2F*.rs%2Cpolkadot%2Fbridges%2Fmodules%2F*%2Fsrc%2Fweights.rs%2Ccumulus%2F**%2Fweights%2F*.rs%2Ccumulus%2F**%2Fweights%2Fxcm%2F*.rs%2Ccumulus%2F**%2Fsrc%2Fweights.rs)

Note: Raw weights change does not mean much here, as this PR reduce the
scope of what is benchmarked, they are therefore decreased by a good
margin. One should instead print the Schedule using

cargo test --features runtime-benchmarks bench_print_schedule --
--nocapture
or following the instructions from the
[README](https://github.com/paritytech/polkadot-sdk/tree/pg/bench_tweaks/substrate/frame/contracts#schedule)
for looking at the Schedule of a specific runtime

---------

Co-authored-by: command-bot <>

**Update:** Pushed additional changes based on the review comments.

**This pull request fixes various spelling mistakes in this
repository.**

Most of the changes are contained in the first **3** commits:

- `Fix spelling mistakes in comments and docs`

- `Fix spelling mistakes in test names`

- `Fix spelling mistakes in error messages, panic messages, logs and
tracing`

Other source code spelling mistakes are separated into individual
commits for easier reviewing:

- `Fix the spelling of 'authority'`

- `Fix the spelling of 'REASONABLE_HEADERS_IN_JUSTIFICATION_ANCESTRY'`

- `Fix the spelling of 'prev_enqueud_messages'`

- `Fix the spelling of 'endpoint'`

- `Fix the spelling of 'children'`

- `Fix the spelling of 'PenpalSiblingSovereignAccount'`

- `Fix the spelling of 'PenpalSudoAccount'`

- `Fix the spelling of 'insufficient'`

- `Fix the spelling of 'PalletXcmExtrinsicsBenchmark'`

- `Fix the spelling of 'subtracted'`

- `Fix the spelling of '...

Introduces `CryptoBytes` type defined as:

```rust
pub struct CryptoBytes<const N: usize, Tag = ()>(pub [u8; N], PhantomData<fn() -> Tag>);
```

The type implements a bunch of methods and traits which are typically
expected from a byte array newtype
(NOTE: some of the methods and trait implementations IMO are a bit
redundant, but I decided to maintain them all to not change too much
stuff in this PR)

It also introduces two (generic) typical consumers of `CryptoBytes`:
`PublicBytes` and `SignatureBytes`.

```rust
pub struct PublicTag;
pub PublicBytes<const N: usize, CryptoTag> = CryptoBytes<N, (PublicTag, CryptoTag)>;

pub struct SignatureTag;
pub SignatureBytes<const N: usize, CryptoTag> = CryptoBytes<N, (SignatureTag, CryptoTag)>;
```

Both of them use a tag to differentiate the two types at a higher level.
Downstream specializations will further specialize using a dedicated
crypto tag. For example in ECDSA:


```rust
pub struct EcdsaTag;

pub type Public = PublicBytes<PUBLIC_KEY_SERIALIZED_SIZE, EcdsaTag>;
pub type Signature = PublicBytes<PUBLIC_KEY_SERIALIZED_SIZE, EcdsaTag>;
```

Overall we have a cleaner and most importantly **consistent** code for
all the types involved

All these details are opaque to the end user which can use `Public` and
`Signature` for the cryptos as before

Remove `#[unstable]` on `call_v2`, `instantiate_v2`,
`lock_delegate_dependency` and `unlock_delegate_dependency`.
See ink! integrations: 
- call_v2: https://github.com/paritytech/ink/pull/2077
- instantiate_v2: <TODO>
- lock/unlock dependency: https://github.com/paritytech/ink/pull/2076

## Xcm changes:
- Fix `pallet_xcm::execute`, move the logic into The `ExecuteController`
so it can be shared with anything that implement that trait.
- Make `ExecuteController::execute` retursn `DispatchErrorWithPostInfo`
instead of `DispatchError`, so that we don't charge the full
`max_weight` provided if the execution is incomplete (useful for
force_batch or contracts calls)
- Fix docstring for `pallet_xcm::execute`, to reflect the changes from
#2405
- Update the signature for `ExecuteController::execute`, we don't need
to return the `Outcome` anymore since we only care about
`Outcome::Complete`

## Contracts changes:

- Update host fn `xcm_exexute`, we don't need to write the `Outcome` to
the sandbox memory anymore. This was also not charged as well before so
it if fixes this too.
- One of the issue was that the dry_run of a contract that call
`xcm_execute` would exhaust the `gas_limit`.

This is because `XcmExecuteController::execute` takes a `max_weight`
argument, and since we don't want the user to specify it manually we
were passing everything left by pre-charghing
`ctx.ext.gas_meter().gas_left()`

- To fix it I added a `fn influence_lowest_limit` on the `Token` trait
and make it return false for `RuntimeCost::XcmExecute`.
- Got rid of the `RuntimeToken` indirection, we can just use
`RuntimeCost` directly.

---------

Co-authored-by: command-bot <>

When doing a cross contract call you can supply an optional Weight limit
for that call. If one doesn't specify the limit (setting it to 0) the
sub call will have all the remaining gas available. If one does specify
the limit we subtract that amount eagerly from the Weight meter and fail
fast if not enough `Weight` is available.

This is quite annoying because setting a fixed limit will set the
`gas_required` in the gas estimation according to the specified limit.
Even if in that dry-run the actual call didn't consume that whole
amount. It effectively discards the more precise measurement it should
have from the dry-run.

This PR changes the behaviour so that the supplied limit is an actual
limit: We do the cross contract call even if the limit is higher than
the remaining `Weight`. We then fail and roll back in the cub call in
case there is not enough weight.

This makes the weight estimation in the dry-run no longer dependent on
the weight limit supplied when doing a cross contract call.

---------

Co-authored-by: PG Herveou <pgherveou@gmail.com>

see #2189

This PR does the following:
- Bring the user api functions into a new pallet-contracts-uapi (They
are currently defined in ink!
[here])(https://github.com/paritytech/ink/blob/master/crates/env/src/engine/on_chain/ext.rs)
- Add older api versions and unstable to the user api trait.
- Remove pallet-contracts-primitives and bring the types it defined in
uapi / pallet-contracts
- Add the infrastructure to build fixtures from Rust files and test it
works by replacing `dummy.wat` and `call.wat`
- Move all the doc from wasm/runtime.rs to pallet-contracts-uapi.

This will be done in a follow up:
- convert the rest of the test from .wat to rust
- bring risc-v uapi up to date with wasm
- finalize the uapi host fns, making sure everything is codegen from the
source host fns in pallet-contracts

---------

Co-authored-by: Alexander Theißen <alex.theissen@me.com>

# Description
We derive few useful traits on `ErrorOrigin` and `ExecError`, including
`codec::Encode` and `codec::Decode`, so that `ExecResult` is
en/decodable as well. This is required for a contract mocking feature
(already prepared in drink:
https://github.com/Cardinal-Cryptography/drink/pull/61). In more detail:
`ExecResult` must be passed from runtime extension, through runtime
interface, back to the pallet, which requires that it is serializable to
bytes in some form (or implements some rare, auxiliary traits).

**Impact on runtime size**: Since most of these traits is used directly
in the pallet now, compiler should be able to throw it out (and thus we
bring no new overhead). However, they are very useful in secondary tools
like drink or other testing libraries.

# Checklist

- [x] My PR includes a detailed description as outlined in the
"Description" section above
- [ ] My PR follows the [labeling requirements](CONTRIBUTING.md#Process)
of this project (at minimum one label for `T`
  required)
- [x] I have made corresponding changes to the documentation (if
applicable)
- [x] I have added tests that prove my fix is effective or that my
feature works (if applicable)

# Description
This PR introduces two changes:
- the previous `Tracing` trait has been modified to accept contract
address instead of code hash (seems to be way more convenient)
- a new trait `CallInterceptor` that allows intercepting contract calls;
in particular the default implementation for `()` will just proceed in a
standard way (after compilation optimizations, there will be no
footprint of that); however, implementing type might decide to mock
invocation and return `ExecResult` instead

Note: one might try merging `before_call` and `intercept_call`. However,
IMHO this would be bad, since it would mix two completely different
abstractions - tracing without any effects and actual intervention into
execution process.

This will unblock working on mocking contracts utility in drink and
similar tools (https://github.com/Cardinal-Cryptography/drink/issues/33)

# Checklist

- [x] My PR includes a detailed description as outlined in the
"Description" section above
- [ ] My PR follows the [labeling
requirements](https://github.com/paritytech/polkadot-sdk/blob/master/docs/CONTRIBUTING.md#process)
of this project (at minimum one label for `T` required)
- [x] I have made corresponding changes to the documentation (if
applicable)
- [x] I have added tests that prove my fix is effective or that my
feature works (if applicable)

Fixes #116 

Start function wasn't allowed in a contract. Now it is allowed and is
being run.

It was disallowed because it is not used by Rust and supporting it made
the code more complex. However, not running the start function violates
the wasm standard. This makes life harder for some languages (see linked
ticket).