Track procedure program depedencies

Author: janezpodhostnik

fvm/environment/facade_env.go

@@ -286,6 +286,7 @@ func (env *facadeEnvironment) FlushPendingUpdates() (
 func (env *facadeEnvironment) Reset() {
 	env.ContractUpdater.Reset()
 	env.EventEmitter.Reset()
+	env.Programs.Reset()
 }
 
 // Miscellaneous cadence runtime.Interface API.

fvm/environment/programs.go

@@ -59,6 +59,13 @@ func NewPrograms(
 	}
 }
 
+// Reset resets the program cache.
+// this is called if the transactions happy path fails.
+func (programs *Programs) Reset() {
+	programs.nonAddressPrograms = make(map[common.Location]*interpreter.Program)
+	programs.dependencyStack = newDependencyStack()
+}
+
 // GetOrLoadProgram gets the program from the cache,
 // or loads it (by calling load) if it is not in the cache.
 // When loading a program, this method will be re-entered
@@ -288,9 +295,18 @@ type dependencyStack struct {
 }
 
 func newDependencyStack() *dependencyStack {
-	return &dependencyStack{
+	stack := &dependencyStack{
 		trackers: make([]dependencyTracker, 0),
 	}
+
+	// The root of the stack is the program (script/transaction) that is being executed.
+	// At the end of the transaction execution, this will hold all the dependencies
+	// of the script/transaction.
+	//
+	// The root of the stack should never be popped.
+	stack.push(common.StringLocation("^ProgramDependencyStackRoot$"))
+
+	return stack
 }
 
 // push a new location to track dependencies for.
@@ -311,17 +327,16 @@ func (s *dependencyStack) push(loc common.Location) {
 func (s *dependencyStack) add(dependencies derived.ProgramDependencies) {
 	l := len(s.trackers)
 	if l == 0 {
-		// stack is empty.
-		// This is expected if loading a program that is already cached.
-		return
+		// This cannot happen, as the root of the stack is always present.
+		panic("Dependency stack unexpectedly empty")
 	}
 
 	s.trackers[l-1].dependencies.Merge(dependencies)
 }
 
 // pop the last dependencies on the stack and return them.
 func (s *dependencyStack) pop() (common.Location, derived.ProgramDependencies, error) {
-	if len(s.trackers) == 0 {
+	if len(s.trackers) <= 1 {
 		return nil,
 			derived.NewProgramDependencies(),
 			fmt.Errorf("cannot pop the programs dependency stack, because it is empty")
@@ -331,14 +346,11 @@ func (s *dependencyStack) pop() (common.Location, derived.ProgramDependencies, e
 	tracker := s.trackers[len(s.trackers)-1]
 	s.trackers = s.trackers[:len(s.trackers)-1]
 
-	// there are more trackers in the stack.
-	// add the dependencies of the popped tracker to the parent tracker
+	// Add the dependencies of the popped tracker to the parent tracker
 	// This is an optimisation to avoid having to iterate through the entire stack
 	// everytime a dependency is pushed or added, instead we add the popped dependencies to the new top of the stack.
 	// (because if C depends on B which depends on A, A's dependencies include C).
-	if len(s.trackers) > 0 {
-		s.trackers[len(s.trackers)-1].dependencies.Merge(tracker.dependencies)
-	}
+	s.trackers[len(s.trackers)-1].dependencies.Merge(tracker.dependencies)
 
 	return tracker.location, tracker.dependencies, nil
 }