Detect use of `block.timestamp` when running `forge coverage` with `--ir-minimum` enabled

[PaulRBerg]

Component

Forge

Describe the feature you would like

Problem

block.timestamp is assumed to be constant when --ir-minimum (via IR) is enabled, and this leads to false negative failed tests when the tests use the warp cheat.

This can easily create hard-to-debug circumstances - tests that normally pass start failing, and debugging via IR-enabled code is not easy.

For instance, I spent an hour debugging one of our tests.

Solution

Detect the use of block.timestamp in the users' tests, and throw a bespoke warning (or error, if the user specifies so via a config field) about it. Recommend using vm.getBlockTimestamp() instead.

Additional context

Related

• block.timestamp bugs when using skip #6180
• Warping not compatible with --optimize true and --via-ir #10683
• bug(forge coverage): stack too deep when using --ir-minimum and coverage report is not accurate #3357

[zerosnacks]

This makes sense to me, could we use a lint prepass for this @0xrusowsky?

[0xrusowsky]

This makes sense to me, could we use a lint prepass for this?

indeed, this should be feasible.

however, rather than building a dedicated pipeline for the forge coverage scenario, should we simply add an informational lint that only runs on tests, to always prompt people to use vm.getBlockTimestamp() instead?

[zerosnacks]

Sounds good to prompt an informational here on use of block.timestamp and block.number. This may also be an issue for other variables usually accessed on block (like https://getfoundry.sh/reference/cheatcodes/prevrandao) so we should review this. Can we limit it to when the IR pipeline is activated? In regular mode these (assumed) constants are not inlined.