hevm: enchanced control over blockchain context #716

d-xo · 2021-07-29T10:36:29Z

Adds a DAPP_TEST_NONCE env var that allows users to control the nonce assigned to the test contract
Adds unit tests for the various DAPP_TEST_* env vars

cc: @kmbarry1 you were asking for this a while back I believe?

nix/build-dapp-package.nix

asymmetric · 2021-07-29T18:12:48Z

nix/build-dapp-package.nix

@@ -47,6 +48,7 @@ in
          '')
          passthru.libPaths;
      buildPhase = ''
+        ln -s ${pkgs.writeText "dapprc" dapprc} ./.dapprc


Instead of this, it could be nice to have the option to pass a dapprc explicitly as an argument (to dapp build I guess?).

Another (unrelated) nit is that .dapprc should probably be (first) looked up in XDG_CONFIG_HOME (which is not cross-compatible with macOS so would introduce some complexity)

kmbarry1 · 2021-07-29T20:43:38Z

cc: @kmbarry1 you were asking for this a while back I believe?

Hey! Yeah, this gets partially at what I was thinking of. The even more powerful thing would actually be what you suggested in chat, a general hevm cheat code for setting any env value, i.e. hevm.set("nonce", N) or hevm.set("currentAddress", 0x1234), etc.

d-xo · 2021-07-29T20:52:55Z

Yeah definitely agree re: the cheat code, but that's a bit of a bigger job for another day.

kmbarry1 · 2021-07-29T21:45:40Z

Yeah definitely agree re: the cheat code, but that's a bit of a bigger job for another day.

Sounds good--and I might still take a crack at it if ever I have some free time 😅 .

d-xo · 2021-08-02T19:27:49Z

So I ended up adding the cheatcodes.

I played around with a cheatcode that could change the address of any contract (hevm.file("address", usr, newAddress)), but there are quite a few places in hevm where we expect addresses to stay constant (e.g. we make multiple calls into the same address when running unit tests), and it just felt like it was gonna be more trouble than it was worth to add.

In the end I added the following:

/*
    allows setting the nonce and balance of an arbitrary account:

      hevm.file("nonce", usr, amt)
      hevm.file("balance", usr, amt)
*/
hevm.file(bytes32, address, uint)

/*
    allows setting the caller, origin, and coinbase:

      hevm.file("caller", usr)
      hevm.file("origin", usr)
      hevm.file("coinbase", usr)
*/
hevm.file(bytes32, address)

/*
    allows setting gas price, tx gas limit, block gas limit, and difficulty:

      hevm.file("gasPrice", amt)
      hevm.file("txGasLimit", amt)
      hevm.file("blockGasLimit", amt)
      hevm.file("difficulty", amt)
*/
hevm.file(bytes32, uint)

/*
    allows reading the nonce for any address:

      hevm.look("nonce", usr);
*/
hevm.look(bytes32, address)

/*
    allows reading the txGasLimit

      hevm.look("txGasLimit");
*/
hevm.look(bytes32)

/*
    allows replacing the code at any address (except the currently executing contract)
*/
hevm.replace(address, bytes)

I think these give almost exactly the same level of control as the DAPP_TEST* env vars, but inside of unit tests via cheat codes. I wasn't completely sure about the interface for the look cheat codes, since they both only have one allowed value for the bytes32 param, but I kinda liked the consistency of the interface, open to suggestions if someone has a better idea.

@kmbarry1 I think with replace and file("nonce", val) you should be able to do what you wanted with bytecode verification? I think you should be able to use replace to set the code of the adress you want to deploy from to a contract that just deploys the contract you want to verify and use file to set the nonce. Is that enough or did you need something more?

d-xo · 2021-08-02T19:28:31Z

src/hevm/CHANGELOG.md

@@ -2,6 +2,10 @@

 ## Unreleased

+### Added


TODO: document new cheatcodes....

transmissions11 · 2021-08-02T19:49:23Z

hollllyyyy cow this is amazing @d-xo. only thing that i think is left out that i would kill to have is the ability to change the address of the test contract like you can with DAPP_TEST_ADDRESS but I know you said thats infeasible 😭

src/hevm/src/EVM.hs

d-xo · 2021-08-02T21:12:46Z

src/dapp-tests/pass/cheatCodes.sol

+        assertEq(who.balance, bal);
+    }
+
+    function testReplace() public {


no idea why at all, but if I construct the target contract directly with the code below in the test instead of in the constructor this test always fails (and it does so before reaching the call to the cheatcode).... 🤔

Suggested change

function testReplace() public {

function testReplace() public {

Old target = new Old();

Hmm, strange indeed. Does it revert or what is the error?

Failure: testReplace src/env.sol:CheatCodes ├╴constructor │ └╴create <unknown contract>@0xCe71065D4017F316EC606Fe4422e11eB2c47c246 <no source map> │ └╴← 63 bytes of code └╴testReplace() └╴error Revert 0x <no source map>

d-xo · 2021-08-03T11:04:48Z

only thing that i think is left out that i would kill to have is the ability to change the address of the test contract like you can with DAPP_TEST_ADDRESS

@TransmissionsDev Do you have an example of something that you could do with mutable adresses that you cannot do with mutable code?

src/hevm/src/EVM.hs

transmissions11 · 2021-08-03T15:13:17Z

only thing that i think is left out that i would kill to have is the ability to change the address of the test contract like you can with DAPP_TEST_ADDRESS

@TransmissionsDev Do you have an example of something that you could do with mutable adresses that you cannot do with mutable code?

no, just more convenient hehe. if i was forking mainnet and wanted to adopt the address of some authorized user, much easier to just go hevm.become(0xaa); thing.auth(); vs having to deploy a new contract, that has a method to call auth, etc

will still be awesome tho, forgot about the type(TestContract).creationCode syntax, was imagining it would be harder to load in bytecode

MrChico · 2021-08-05T11:04:29Z

src/hevm/src/EVM.hs

+                   assign (env . contracts . (ix usr) . codeOps) $ mkCodeOps newCode
+                   assign (env . contracts . (ix usr) . opIxMap) $ mkOpIxMap newCode
+                   assign (env . contracts . (ix usr) . contractcode) $ RuntimeCode newCode
+                   assign (cache . fetched . (ix usr) . contractcode) $ RuntimeCode newCode


not sure this is safe. The cache should only contain rpc queries

MrChico · 2021-09-04T09:53:29Z

src/hevm/src/EVM.hs

+                _ -> vmError (BadCheatCode sig)
+            _ -> vmError (BadCheatCode sig),
+
+      action "replace(address,bytes)" $


an alternative to this could be move(src,dst) which also moves storage (and nonce and balance?) from the src to dst address

hevm: add env var to control nonce

dd1ae7a

d-xo requested a review from MrChico July 29, 2021 10:36

d-xo commented Jul 29, 2021

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nix: buildDappPackage: use real dapprc

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d-xo added 3 commits July 30, 2021 14:33

hevm: add look and file cheatcodes

4f4bd40

hevm: dev: add some new opts to ghciTest

b934e8f

hevm: rm address replacement cheatcode, add code replacement cheatcode

51fdbaa

d-xo changed the title ~~hevm: add env var to control nonce~~ hevm: enchanced control over blockchain context Aug 2, 2021

d-xo commented Aug 2, 2021

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src/hevm/CHANGELOG.md

@@ -2,6 +2,10 @@

## Unreleased

### Added

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TODO: document new cheatcodes....

d-xo commented Aug 2, 2021

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hevm: don't modify vm after vmError

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hevm: enchanced control over blockchain context #716

hevm: enchanced control over blockchain context #716

d-xo commented Jul 29, 2021

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	function testReplace() public {
	function testReplace() public {
	Old target = new Old();

hevm: enchanced control over blockchain context #716

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hevm: enchanced control over blockchain context #716

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