command/providers: Show provider requirements tree

Providers can be required from multiple sources. The previous
implementation of the providers sub-command displayed only a flat list
of provider requirements, which made it difficult to see which modules
required each provider.

This commit reintroduces the tree display of provider requirements, and
adds a separate output block for providers required by existing state.

command/providers.go

@@ -94,23 +94,32 @@ func (c *ProvidersCommand) Run(args []string) int {
 		return 1
 	}
 
-	reqs, reqDiags := config.ProviderRequirements()
-	if reqDiags.HasErrors() {
-		c.showDiagnostics(configDiags)
+	reqs, reqDiags := config.ProviderRequirementsByModule()
+	diags = diags.Append(reqDiags)
+	if diags.HasErrors() {
+		c.showDiagnostics(diags)
 		return 1
 	}
 
 	state := s.State()
+	var stateReqs getproviders.Requirements
 	if state != nil {
-		stateReqs := state.ProviderRequirements()
-		reqs = reqs.Merge(stateReqs)
+		stateReqs = state.ProviderRequirements()
 	}
 
 	printRoot := treeprint.New()
-	providersCommandPopulateTreeNode(printRoot, reqs)
+	c.populateTreeNode(printRoot, reqs)
 
+	c.Ui.Output("\nProviders required by configuration:")
 	c.Ui.Output(printRoot.String())
 
+	if len(stateReqs) > 0 {
+		c.Ui.Output("Providers required by state:\n")
+		for fqn := range stateReqs {
+			c.Ui.Output(fmt.Sprintf("    provider[%s]\n", fqn.String()))
+		}
+	}
+
 	c.showDiagnostics(diags)
 	if diags.HasErrors() {
 		return 1
@@ -118,22 +127,27 @@ func (c *ProvidersCommand) Run(args []string) int {
 	return 0
 }
 
-func providersCommandPopulateTreeNode(node treeprint.Tree, deps getproviders.Requirements) {
-	for fqn, dep := range deps {
+func (c *ProvidersCommand) populateTreeNode(tree treeprint.Tree, node *configs.ModuleRequirements) {
+	for fqn, dep := range node.Requirements {
 		versionsStr := getproviders.VersionConstraintsString(dep)
 		if versionsStr != "" {
 			versionsStr = " " + versionsStr
 		}
-		node.AddNode(fmt.Sprintf("provider[%s]%s", fqn.String(), versionsStr))
+		tree.AddNode(fmt.Sprintf("provider[%s]%s", fqn.String(), versionsStr))
+	}
+	for name, childNode := range node.Children {
+		branch := tree.AddBranch(fmt.Sprintf("module.%s", name))
+		c.populateTreeNode(branch, childNode)
 	}
 }
 
 const providersCommandHelp = `
 Usage: terraform providers [dir]
 
-  Prints out a list of providers required by the configuration and state.
+  Prints out a tree of modules in the referenced configuration annotated with
+  their provider requirements.
 
-  This provides an overview of all of the provider requirements as an aid to
-  understanding why particular provider plugins are needed and why particular
-  versions are selected.
+  This provides an overview of all of the provider requirements across all
+  referenced modules, as an aid to understanding why particular provider
+  plugins are needed and why particular versions are selected.
 `

command/providers_test.go

@@ -5,6 +5,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/hashicorp/terraform/helper/copy"
 	"github.com/mitchellh/cli"
 )
 
@@ -75,14 +76,10 @@ func TestProviders_noConfigs(t *testing.T) {
 }
 
 func TestProviders_modules(t *testing.T) {
-	cwd, err := os.Getwd()
-	if err != nil {
-		t.Fatalf("err: %s", err)
-	}
-	if err := os.Chdir(testFixturePath("providers/modules")); err != nil {
-		t.Fatalf("err: %s", err)
-	}
-	defer os.Chdir(cwd)
+	td := tempDir(t)
+	copy.CopyDir(testFixturePath("providers/modules"), td)
+	defer os.RemoveAll(td)
+	defer testChdir(t, td)()
 
 	// first run init with mock provider sources to install the module
 	initUi := new(cli.MockUi)
@@ -120,7 +117,8 @@ func TestProviders_modules(t *testing.T) {
 	wantOutput := []string{
 		"provider[registry.terraform.io/hashicorp/foo] 1.0.*", // from required_providers
 		"provider[registry.terraform.io/hashicorp/bar] 2.0.0", // from provider config
-		"provider[registry.terraform.io/hashicorp/baz]",       // implied by a resource in the child module
+		"── module.kiddo",                               // tree node for child module
+		"provider[registry.terraform.io/hashicorp/baz]", // implied by a resource in the child module
 	}
 
 	output := ui.OutputWriter.String()
@@ -156,6 +154,7 @@ func TestProviders_state(t *testing.T) {
 	wantOutput := []string{
 		"provider[registry.terraform.io/hashicorp/foo] 1.0.*", // from required_providers
 		"provider[registry.terraform.io/hashicorp/bar] 2.0.0", // from a provider config block
+		"Providers required by state",                         // header for state providers
 		"provider[registry.terraform.io/hashicorp/baz]",       // from a resouce in state (only)
 	}
 

command/testdata/providers/modules/main.tf

@@ -10,6 +10,6 @@ provider "bar" {
   version = "2.0.0"
 }
 
-module "child" {
+module "kiddo" {
   source = "./child"
 }

configs/config.go

@@ -77,6 +77,15 @@ type Config struct {
 	Version *version.Version
 }
 
+// ModuleRequirements represents the provider requirements for an individual
+// module, along with references to any child modules. This is used to
+// determine which modules require which providers.
+type ModuleRequirements struct {
+	Module       *Module
+	Requirements getproviders.Requirements
+	Children     map[string]*ModuleRequirements
+}
+
 // NewEmptyConfig constructs a single-node configuration tree with an empty
 // root module. This is generally a pretty useless thing to do, so most callers
 // should instead use BuildConfig.
@@ -175,12 +184,45 @@ func (c *Config) DescendentForInstance(path addrs.ModuleInstance) *Config {
 func (c *Config) ProviderRequirements() (getproviders.Requirements, hcl.Diagnostics) {
 	reqs := make(getproviders.Requirements)
 	diags := c.addProviderRequirements(reqs)
+
+	for _, childConfig := range c.Children {
+		moreDiags := childConfig.addProviderRequirements(reqs)
+		diags = append(diags, moreDiags...)
+	}
+
 	return reqs, diags
 }
 
+// ProviderRequirementsByModule searches the full tree of modules under the
+// receiver for both explicit and implicit dependencies on providers,
+// constructing a tree where the requirements are broken out by module.
+//
+// If the returned diagnostics includes errors then the resulting Requirements
+// may be incomplete.
+func (c *Config) ProviderRequirementsByModule() (*ModuleRequirements, hcl.Diagnostics) {
+	reqs := make(getproviders.Requirements)
+	diags := c.addProviderRequirements(reqs)
+
+	children := make(map[string]*ModuleRequirements)
+	for name, child := range c.Children {
+		childReqs, childDiags := child.ProviderRequirementsByModule()
+		children[name] = childReqs
+		diags = append(diags, childDiags...)
+	}
+
+	ret := &ModuleRequirements{
+		Module:       c.Module,
+		Requirements: reqs,
+		Children:     children,
+	}
+
+	return ret, diags
+}
+
 // addProviderRequirements is the main part of the ProviderRequirements
 // implementation, gradually mutating a shared requirements object to
-// eventually return.
+// eventually return. This function only adds requirements for the top-level
+// module.
 func (c *Config) addProviderRequirements(reqs getproviders.Requirements) hcl.Diagnostics {
 	var diags hcl.Diagnostics
 
@@ -235,13 +277,6 @@ func (c *Config) addProviderRequirements(reqs getproviders.Requirements) hcl.Dia
 		}
 	}
 
-	// ...and now we'll recursively visit all of the child modules to merge
-	// in their requirements too.
-	for _, childConfig := range c.Children {
-		moreDiags := childConfig.addProviderRequirements(reqs)
-		diags = append(diags, moreDiags...)
-	}
-
 	return diags
 }
 

configs/config_test.go

@@ -5,7 +5,11 @@ import (
 
 	"github.com/go-test/deep"
 	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
+	"github.com/zclconf/go-cty/cty"
 
+	version "github.com/hashicorp/go-version"
+	"github.com/hashicorp/hcl/v2/hclsyntax"
 	svchost "github.com/hashicorp/terraform-svchost"
 	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/internal/getproviders"
@@ -145,6 +149,59 @@ func TestConfigProviderRequirements(t *testing.T) {
 	}
 }
 
+func TestConfigProviderRequirementsByModule(t *testing.T) {
+	cfg, diags := testNestedModuleConfigFromDir(t, "testdata/provider-reqs")
+	assertNoDiagnostics(t, diags)
+
+	tlsProvider := addrs.NewProvider(
+		addrs.DefaultRegistryHost,
+		"hashicorp", "tls",
+	)
+	happycloudProvider := addrs.NewProvider(
+		svchost.Hostname("tf.example.com"),
+		"awesomecorp", "happycloud",
+	)
+	nullProvider := addrs.NewDefaultProvider("null")
+	randomProvider := addrs.NewDefaultProvider("random")
+	impliedProvider := addrs.NewDefaultProvider("implied")
+	terraformProvider := addrs.NewBuiltInProvider("terraform")
+	configuredProvider := addrs.NewDefaultProvider("configured")
+
+	got, diags := cfg.ProviderRequirementsByModule()
+	assertNoDiagnostics(t, diags)
+	child, ok := cfg.Children["kinder"]
+	if !ok {
+		t.Fatalf(`could not find child config "kinder" in config children`)
+	}
+	want := &ModuleRequirements{
+		Module: cfg.Module,
+		Requirements: getproviders.Requirements{
+			// Only the root module's version is present here
+			nullProvider:       getproviders.MustParseVersionConstraints("~> 2.0.0"),
+			randomProvider:     getproviders.MustParseVersionConstraints("~> 1.2.0"),
+			tlsProvider:        getproviders.MustParseVersionConstraints("~> 3.0"),
+			configuredProvider: getproviders.MustParseVersionConstraints("~> 1.4"),
+			impliedProvider:    nil,
+			terraformProvider:  nil,
+		},
+		Children: map[string]*ModuleRequirements{
+			"kinder": {
+				Module: child.Module,
+				Requirements: getproviders.Requirements{
+					nullProvider:       getproviders.MustParseVersionConstraints("= 2.0.1"),
+					happycloudProvider: nil,
+				},
+				Children: map[string]*ModuleRequirements{},
+			},
+		},
+	}
+
+	ignore := cmpopts.IgnoreUnexported(version.Constraint{}, cty.Value{}, hclsyntax.Body{})
+	if diff := cmp.Diff(want, got, ignore); diff != "" {
+		t.Errorf("wrong result\n%s", diff)
+	}
+}
+
 func TestConfigProviderForConfigAddr(t *testing.T) {
 	cfg, diags := testModuleConfigFromDir("testdata/valid-modules/providers-fqns")
 	assertNoDiagnostics(t, diags)

configs/testdata/provider-reqs/provider-reqs-root.tf

@@ -16,7 +16,7 @@ terraform {
 resource "implied_foo" "bar" {
 }
 
-module "child" {
+module "kinder" {
   source = "./child"
 }