From 934e2261ae413c28e06148df02578e43e955d652 Mon Sep 17 00:00:00 2001
From: Arran Schlosberg <me@arranschlosberg.com>
Date: Thu, 26 Sep 2024 11:02:14 +0100
Subject: [PATCH] feat: `params.RulesHooks.ActivePrecompiles` override

---
 core/vm/contracts.go             |  5 ++++-
 core/vm/contracts.libevm_test.go | 22 ++++++++++++++++++++++
 libevm/hookstest/stub.go         | 10 ++++++++++
 params/hooks.libevm.go           | 11 +++++++++++
 4 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/core/vm/contracts.go b/core/vm/contracts.go
index 00df55eee6b8..cc7c56d0e4fc 100644
--- a/core/vm/contracts.go
+++ b/core/vm/contracts.go
@@ -148,7 +148,10 @@ func init() {
 }
 
 // ActivePrecompiles returns the precompiles enabled with the current configuration.
-func ActivePrecompiles(rules params.Rules) []common.Address {
+func ActivePrecompiles(rules params.Rules) (active []common.Address) {
+	defer func() {
+		active = rules.Hooks().ActivePrecompiles(append([]common.Address{}, active...))
+	}()
 	switch {
 	case rules.IsCancun:
 		return PrecompiledAddressesCancun
diff --git a/core/vm/contracts.libevm_test.go b/core/vm/contracts.libevm_test.go
index d40513f89c48..b28174b38230 100644
--- a/core/vm/contracts.libevm_test.go
+++ b/core/vm/contracts.libevm_test.go
@@ -423,3 +423,25 @@ func TestCanCreateContract(t *testing.T) {
 		})
 	}
 }
+
+func TestActivePrecompilesOverride(t *testing.T) {
+	newRules := func() params.Rules {
+		return new(params.ChainConfig).Rules(big.NewInt(0), false, 0)
+	}
+	defaultActive := vm.ActivePrecompiles(newRules())
+
+	rng := ethtest.NewPseudoRand(0xDecafC0ffeeBad)
+	precompiles := make([]common.Address, rng.Intn(10)+5)
+	for i := range precompiles {
+		precompiles[i] = rng.Address()
+	}
+	hooks := &hookstest.Stub{
+		ActivePrecompilesFn: func(active []common.Address) []common.Address {
+			assert.Equal(t, defaultActive, active, "ActivePrecompiles() hook receives default addresses")
+			return precompiles
+		},
+	}
+	hooks.Register(t)
+
+	require.Equal(t, precompiles, vm.ActivePrecompiles(newRules()), "vm.ActivePrecompiles() returns overridden addresses")
+}
diff --git a/libevm/hookstest/stub.go b/libevm/hookstest/stub.go
index 78fec96f0e75..53df887f8288 100644
--- a/libevm/hookstest/stub.go
+++ b/libevm/hookstest/stub.go
@@ -45,6 +45,7 @@ type Stub struct {
 	CheckConfigCompatibleFn func(*params.ChainConfig, *big.Int, uint64) *params.ConfigCompatError
 	DescriptionSuffix       string
 	PrecompileOverrides     map[common.Address]libevm.PrecompiledContract
+	ActivePrecompilesFn     func([]common.Address) []common.Address
 	CanExecuteTransactionFn func(common.Address, *common.Address, libevm.StateReader) error
 	CanCreateContractFn     func(*libevm.AddressContext, uint64, libevm.StateReader) (uint64, error)
 }
@@ -71,6 +72,15 @@ func (s Stub) PrecompileOverride(a common.Address) (libevm.PrecompiledContract,
 	return p, ok
 }
 
+// ActivePrecompiles proxies arguments to the s.ActivePrecompilesFn function if
+// non-nil, otherwise it acts as a noop.
+func (s Stub) ActivePrecompiles(active []common.Address) []common.Address {
+	if f := s.ActivePrecompilesFn; f != nil {
+		return f(active)
+	}
+	return active
+}
+
 // CheckConfigForkOrder proxies arguments to the s.CheckConfigForkOrderFn
 // function if non-nil, otherwise it acts as a noop.
 func (s Stub) CheckConfigForkOrder() error {
diff --git a/params/hooks.libevm.go b/params/hooks.libevm.go
index 57e40d4f31a9..23e4e27490bf 100644
--- a/params/hooks.libevm.go
+++ b/params/hooks.libevm.go
@@ -48,6 +48,12 @@ type RulesHooks interface {
 	// [PrecompiledContract] is non-nil. If it returns `false` then the default
 	// precompile behaviour is honoured.
 	PrecompileOverride(common.Address) (_ libevm.PrecompiledContract, override bool)
+	// ActivePrecompiles receives the addresses that would usually be returned
+	// by a call to [vm.ActivePrecompiles] and MUST return the value to be
+	// returned by said function, which will be propagated. It MAY alter the
+	// received slice. The value it returns MUST be consistent with the
+	// behaviour of the PrecompileOverride hook.
+	ActivePrecompiles([]common.Address) []common.Address
 }
 
 // RulesAllowlistHooks are a subset of [RulesHooks] that gate actions, signalled
@@ -120,3 +126,8 @@ func (NOOPHooks) CanCreateContract(_ *libevm.AddressContext, gas uint64, _ libev
 func (NOOPHooks) PrecompileOverride(common.Address) (libevm.PrecompiledContract, bool) {
 	return nil, false
 }
+
+// ActivePrecompiles echoes the active addresses unchanged.
+func (NOOPHooks) ActivePrecompiles(active []common.Address) []common.Address {
+	return active
+}