Expander.ExpandResource cannot expand all modules

ExpandResource must only check the specific ModuleInstances in the
requested path, because the resource may not have been registered yet in
all module instances.

instances/expander.go

@@ -136,7 +136,7 @@ func (e *Expander) ExpandModuleResource(moduleAddr addrs.Module, resourceAddr ad
 	// (moduleInstances does plenty of allocations itself, so the benefit of
 	// pre-allocating this is marginal but it's not hard to do.)
 	moduleInstanceAddr := make(addrs.ModuleInstance, 0, 4)
-	ret := e.exps.resourceInstances(moduleAddr, resourceAddr, moduleInstanceAddr)
+	ret := e.exps.moduleResourceInstances(moduleAddr, resourceAddr, moduleInstanceAddr)
 	sort.SliceStable(ret, func(i, j int) bool {
 		return ret[i].Less(ret[j])
 	})
@@ -150,16 +150,14 @@ func (e *Expander) ExpandModuleResource(moduleAddr addrs.Module, resourceAddr ad
 // itself must already have had their expansion registered using one of the
 // SetModule*/SetResource* methods before calling, or this method will panic.
 func (e *Expander) ExpandResource(resourceAddr addrs.AbsResource) []addrs.AbsResourceInstance {
-	var ret []addrs.AbsResourceInstance
+	e.mu.RLock()
+	defer e.mu.RUnlock()
 
-	// Take the full set of expanded resource instances and filter for only
-	// those within our module instance.
-	for _, r := range e.ExpandModuleResource(resourceAddr.Module.Module(), resourceAddr.Resource) {
-		if !r.Module.Equal(resourceAddr.Module) {
-			continue
-		}
-		ret = append(ret, r)
-	}
+	moduleInstanceAddr := make(addrs.ModuleInstance, 0, 4)
+	ret := e.exps.resourceInstances(resourceAddr.Module, resourceAddr.Resource, moduleInstanceAddr)
+	sort.SliceStable(ret, func(i, j int) bool {
+		return ret[i].Less(ret[j])
+	})
 	return ret
 }
 
@@ -297,10 +295,9 @@ func (m *expanderModule) moduleInstances(addr addrs.Module, parentAddr addrs.Mod
 	return ret
 }
 
-func (m *expanderModule) resourceInstances(moduleAddr addrs.Module, resourceAddr addrs.Resource, parentAddr addrs.ModuleInstance) []addrs.AbsResourceInstance {
-	var ret []addrs.AbsResourceInstance
-
+func (m *expanderModule) moduleResourceInstances(moduleAddr addrs.Module, resourceAddr addrs.Resource, parentAddr addrs.ModuleInstance) []addrs.AbsResourceInstance {
 	if len(moduleAddr) > 0 {
+		var ret []addrs.AbsResourceInstance
 		// We need to traverse through the module levels first, so we can
 		// then iterate resource expansions in the context of each module
 		// path leading to them.
@@ -317,11 +314,37 @@ func (m *expanderModule) resourceInstances(moduleAddr addrs.Module, resourceAddr
 				continue
 			}
 			moduleInstAddr := append(parentAddr, step)
-			ret = append(ret, inst.resourceInstances(moduleAddr[1:], resourceAddr, moduleInstAddr)...)
+			ret = append(ret, inst.moduleResourceInstances(moduleAddr[1:], resourceAddr, moduleInstAddr)...)
 		}
 		return ret
 	}
 
+	return m.onlyResourceInstances(resourceAddr, parentAddr)
+}
+
+func (m *expanderModule) resourceInstances(moduleAddr addrs.ModuleInstance, resourceAddr addrs.Resource, parentAddr addrs.ModuleInstance) []addrs.AbsResourceInstance {
+	if len(moduleAddr) > 0 {
+		// We need to traverse through the module levels first, using only the
+		// module instances for our specific resource, as the resource may not
+		// yet be expanded in all module instances.
+		step := moduleAddr[0]
+		callName := step.Name
+		if _, ok := m.moduleCalls[addrs.ModuleCall{Name: callName}]; !ok {
+			// This is a bug in the caller, because it should always register
+			// expansions for an object and all of its ancestors before requesting
+			// expansion of it.
+			panic(fmt.Sprintf("no expansion has been registered for %s", parentAddr.Child(callName, addrs.NoKey)))
+		}
+
+		inst := m.childInstances[step]
+		moduleInstAddr := append(parentAddr, step)
+		return inst.resourceInstances(moduleAddr[1:], resourceAddr, moduleInstAddr)
+	}
+	return m.onlyResourceInstances(resourceAddr, parentAddr)
+}
+
+func (m *expanderModule) onlyResourceInstances(resourceAddr addrs.Resource, parentAddr addrs.ModuleInstance) []addrs.AbsResourceInstance {
+	var ret []addrs.AbsResourceInstance
 	exp, ok := m.resources[resourceAddr]
 	if !ok {
 		panic(fmt.Sprintf("no expansion has been registered for %s", resourceAddr.Absolute(parentAddr)))