refactor: move hooks logic to its own file

Author: ARR4N

core/vm/hooks.libevm.go

@@ -0,0 +1,35 @@
+package vm
+
+import "github.com/ethereum/go-ethereum/params"
+
+// RegisterHooks registers the Hooks. It is expected to be called in an `init()`
+// function and MUST NOT be called more than once.
+func RegisterHooks(h Hooks) {
+	if libevmHooks != nil {
+		panic("already registered")
+	}
+	libevmHooks = h
+}
+
+var libevmHooks Hooks
+
+// Hooks are arbitrary configuration functions to modify default VM behaviour.
+type Hooks interface {
+	// OverrideJumpTable will only be called if
+	// [params.RulesHooks.OverrideJumpTable] returns true. This allows for
+	// recursive calling into [LookupInstructionSet].
+	OverrideJumpTable(params.Rules, *JumpTable) *JumpTable
+}
+
+// overrideJumpTable returns `libevmHooks.OverrideJumpTable(r,jt)“ i.f.f. the
+// Rules' hooks indicate that it must, otherwise it echoes `jt` unchanged.
+func overrideJumpTable(r params.Rules, jt *JumpTable) *JumpTable {
+	if !r.Hooks().OverrideJumpTable() {
+		return jt
+	}
+	// We don't check that libevmHooks is non-nil because the user has clearly
+	// signified that they want an override. A nil-pointer dereference will
+	// occur in tests whereas graceful degradation would frustrate the user with
+	// a hard-to-find bug.
+	return libevmHooks.OverrideJumpTable(r, jt)
+}