terraform: configure provider aliases in the new apply graph

Found via a shadow graph failure:

Provider aliases weren't being configured by the new apply graph.

This was caused by the transform that attaches configs to provider nodes
not being able to handle aliases and therefore not attaching a config.
Added a test to this and fixed it.

terraform/context_apply_test.go

@@ -216,6 +216,60 @@ func TestContext2Apply_providerAlias(t *testing.T) {
 	}
 }
 
+// Two providers that are configured should both be configured prior to apply
+func TestContext2Apply_providerAliasConfigure(t *testing.T) {
+	m := testModule(t, "apply-provider-alias-configure")
+
+	p2 := testProvider("another")
+	p2.ApplyFn = testApplyFn
+	p2.DiffFn = testDiffFn
+
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"another": testProviderFuncFixed(p2),
+		},
+	})
+
+	if p, err := ctx.Plan(); err != nil {
+		t.Fatalf("err: %s", err)
+	} else {
+		t.Logf(p.String())
+	}
+
+	// Configure to record calls AFTER Plan above
+	var configCount int32
+	p2.ConfigureFn = func(c *ResourceConfig) error {
+		atomic.AddInt32(&configCount, 1)
+
+		foo, ok := c.Get("foo")
+		if !ok {
+			return fmt.Errorf("foo is not found")
+		}
+
+		if foo != "bar" {
+			return fmt.Errorf("foo: %#v", foo)
+		}
+
+		return nil
+	}
+
+	state, err := ctx.Apply()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if configCount != 2 {
+		t.Fatalf("provider config expected 2 calls, got: %d", configCount)
+	}
+
+	actual := strings.TrimSpace(state.String())
+	expected := strings.TrimSpace(testTerraformApplyProviderAliasConfigStr)
+	if actual != expected {
+		t.Fatalf("bad: \n%s", actual)
+	}
+}
+
 // GH-2870
 func TestContext2Apply_providerWarning(t *testing.T) {
 	m := testModule(t, "apply-provider-warning")

terraform/terraform_test.go

@@ -286,6 +286,14 @@ aws_instance.foo:
   type = aws_instance
 `
 
+const testTerraformApplyProviderAliasConfigStr = `
+another_instance.bar:
+  ID = foo
+  provider = another.two
+another_instance.foo:
+  ID = foo
+`
+
 const testTerraformApplyEmptyModuleStr = `
 <no state>
 Outputs:

terraform/test-fixtures/apply-provider-alias-configure/main.tf

@@ -0,0 +1,11 @@
+provider "another" {
+    foo = "bar"
+}
+
+provider "another" {
+    alias = "two"
+    foo = "bar"
+}
+
+resource "another_instance" "foo" {}
+resource "another_instance" "bar" { provider = "another.two" }

terraform/transform_attach_config_provider.go

@@ -47,8 +47,6 @@ func (t *AttachProviderConfigTransformer) attachProviders(g *Graph) error {
 			continue
 		}
 
-		// TODO: aliases?
-
 		// Determine what we're looking for
 		path := normalizeModulePath(apn.Path())
 		path = path[1:]
@@ -63,7 +61,14 @@ func (t *AttachProviderConfigTransformer) attachProviders(g *Graph) error {
 
 		// Go through the provider configs to find the matching config
 		for _, p := range tree.Config().ProviderConfigs {
-			if p.Name == name {
+			// Build the name, which is "name.alias" if an alias exists
+			current := p.Name
+			if p.Alias != "" {
+				current += "." + p.Alias
+			}
+
+			// If the configs match then attach!
+			if current == name {
 				log.Printf("[TRACE] Attaching provider config: %#v", p)
 				apn.AttachProvider(p)
 				break