Merge pull request #5772 from hashicorp/phinze/var-concurrent-map-race

terraform: share graph walker's variables lock w/ interpolater

terraform/graph_walk_context.go

@@ -86,6 +86,7 @@ func (w *ContextGraphWalker) EnterPath(path []string) EvalContext {
 			State:         w.Context.state,
 			StateLock:     &w.Context.stateLock,
 			Variables:     variables,
+			VariablesLock: &w.interpolaterVarLock,
 		},
 		InterpolaterVars:    w.interpolaterVars,
 		InterpolaterVarLock: &w.interpolaterVarLock,

terraform/interpolate.go

@@ -28,6 +28,7 @@ type Interpolater struct {
 	State         *State
 	StateLock     *sync.RWMutex
 	Variables     map[string]string
+	VariablesLock *sync.Mutex
 }
 
 // InterpolationScope is the current scope of execution. This is required
@@ -273,6 +274,8 @@ func (i *Interpolater) valueUserVar(
 	n string,
 	v *config.UserVariable,
 	result map[string]ast.Variable) error {
+	i.VariablesLock.Lock()
+	defer i.VariablesLock.Unlock()
 	val, ok := i.Variables[v.Name]
 	if ok {
 		result[n] = ast.Variable{