terraform: test that unused providers are pruned

terraform/graph.go

@@ -234,6 +234,9 @@ func Graph(opts *GraphOpts) (*depgraph.Graph, error) {
 	// Add the provider dependencies
 	graphAddResourceProviderDeps(g)
 
+	// Now, prune the providers that we aren't using.
+	graphPruneResourceProviders(g)
+
 	// Add explicit dependsOn dependencies to the graph
 	graphAddExplicitDeps(g)
 
@@ -1177,6 +1180,47 @@ func graphAddResourceProviderDeps(g *depgraph.Graph) {
 	}
 }
 
+// graphPruneResourceProviders will remove the GraphNodeResourceProvider
+// nodes that aren't used in any way.
+func graphPruneResourceProviders(g *depgraph.Graph) {
+	// First, build a mapping of the providers we have.
+	ps := make(map[string]struct{})
+	for _, n := range g.Nouns {
+		_, ok := n.Meta.(*GraphNodeResourceProvider)
+		if !ok {
+			continue
+		}
+
+		ps[n.Name] = struct{}{}
+	}
+
+	// Now go through all the dependencies throughout and find
+	// if any of these aren't reachable.
+	for _, n := range g.Nouns {
+		for _, dep := range n.Deps {
+			delete(ps, dep.Target.Name)
+		}
+	}
+
+	if len(ps) == 0 {
+		// We used all of them!
+		return
+	}
+
+	// Now go through and remove these nodes that aren't used
+	for i := 0; i < len(g.Nouns); i++ {
+		if _, ok := ps[g.Nouns[i].Name]; !ok {
+			continue
+		}
+
+		// Delete this node
+		copy(g.Nouns[i:], g.Nouns[i+1:])
+		g.Nouns[len(g.Nouns)-1] = nil
+		g.Nouns = g.Nouns[:len(g.Nouns)-1]
+		i--
+	}
+}
+
 // graphMapResourceProviderId goes through the graph and maps the
 // ID of a resource provider node to each resource. This lets us know which
 // configuration is for which resource.

terraform/graph_test.go

@@ -159,6 +159,21 @@ func TestGraph_moduleOrphan(t *testing.T) {
 	}
 }
 
+func TestGraph_providerPrune(t *testing.T) {
+	m := testModule(t, "graph-provider-prune")
+
+	g, err := Graph(&GraphOpts{Module: m})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(g.String())
+	expected := strings.TrimSpace(testTerraformGraphProviderPruneStr)
+	if actual != expected {
+		t.Fatalf("bad:\n\n%s", actual)
+	}
+}
+
 func TestGraph_state(t *testing.T) {
 	m := testModule(t, "graph-basic")
 	state := &State{
@@ -910,6 +925,15 @@ root
   root -> aws_instance.old
 `
 
+const testTerraformGraphProviderPruneStr = `
+root: root
+aws_load_balancer.weblb
+  aws_load_balancer.weblb -> provider.aws
+provider.aws
+root
+  root -> aws_load_balancer.weblb
+`
+
 const testTerraformGraphStateStr = `
 root: root
 aws_instance.old

terraform/test-fixtures/graph-provider-prune/main.tf

@@ -0,0 +1,5 @@
+provider "aws" {}
+provider "digitalocean" {}
+provider "openstack" {}
+
+resource "aws_load_balancer" "weblb" {}