terraform: import graph should setup parent refs to providers

Fixes #11212

The import graph builder was missing the transform to setup links to
parent providers, so provider inheritance didn't work properly. This
adds that.

This also removes the `PruneProviderTransform` since that has no value
in this graph since we'll never add an unused provider.

terraform/context_import_test.go

@@ -208,6 +208,53 @@ func TestContextImport_moduleProvider(t *testing.T) {
 	}
 }
 
+// Test that import sets up the graph properly for provider inheritance
+func TestContextImport_providerInherit(t *testing.T) {
+	p := testProvider("aws")
+	ctx := testContext2(t, &ContextOpts{
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+	})
+
+	p.ImportStateReturn = []*InstanceState{
+		&InstanceState{
+			ID:        "foo",
+			Ephemeral: EphemeralState{Type: "aws_instance"},
+		},
+	}
+
+	configured := false
+	p.ConfigureFn = func(c *ResourceConfig) error {
+		configured = true
+
+		if v, ok := c.Get("foo"); !ok || v.(string) != "bar" {
+			return fmt.Errorf("bad")
+		}
+
+		return nil
+	}
+
+	m := testModule(t, "import-provider-inherit")
+
+	_, err := ctx.Import(&ImportOpts{
+		Module: m,
+		Targets: []*ImportTarget{
+			&ImportTarget{
+				Addr: "module.child.aws_instance.foo",
+				ID:   "bar",
+			},
+		},
+	})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if !configured {
+		t.Fatal("didn't configure provider")
+	}
+}
+
 // Test that import will interpolate provider configuration and use
 // that configuration for import.
 func TestContextImport_providerVarConfig(t *testing.T) {

terraform/graph_builder_import.go

@@ -47,7 +47,7 @@ func (b *ImportGraphBuilder) Steps() []GraphTransformer {
 
 	steps := []GraphTransformer{
 		// Create all our resources from the configuration and state
-		&ConfigTransformerOld{Module: mod},
+		&ConfigTransformer{Module: mod},
 
 		// Add the import steps
 		&ImportStateTransformer{Targets: b.ImportTargets},
@@ -55,8 +55,8 @@ func (b *ImportGraphBuilder) Steps() []GraphTransformer {
 		// Provider-related transformations
 		&MissingProviderTransformer{Providers: b.Providers, Concrete: concreteProvider},
 		&ProviderTransformer{},
-		&DisableProviderTransformerOld{},
-		&PruneProviderTransformer{},
+		&DisableProviderTransformer{},
+		&ParentProviderTransformer{},
 		&AttachProviderConfigTransformer{Module: mod},
 
 		// This validates that the providers only depend on variables

terraform/test-fixtures/import-provider-inherit/child/main.tf

@@ -0,0 +1 @@
+# Empty

terraform/test-fixtures/import-provider-inherit/main.tf

@@ -0,0 +1,5 @@
+provider "aws" {
+  foo = "bar"
+}
+
+module "child" { source = "./child" }