command/providers: refactor with new provider types and functions

The providers command has been refactored to use the modern provider types and
ProviderRequirements() functions. This resulted in a breaking change to
the output: it no longer outputs the providers by module and no longer
prints `(inherited)` or `(from state)` to show why a provider is
included. We decided that at this time it was best to stick with the
existing functions and make this change, but if we get feedback from the
community we will revisit.

Additional tests to exercise providers in modules and providers from
state have been included.

command/providers.go

@@ -2,9 +2,11 @@ package command
 
 import (
 	"fmt"
+	"path/filepath"
 
-	"github.com/hashicorp/terraform/addrs"
-	"github.com/hashicorp/terraform/moduledeps"
+	"github.com/hashicorp/terraform/configs"
+	"github.com/hashicorp/terraform/internal/getproviders"
+	"github.com/hashicorp/terraform/tfdiags"
 	"github.com/xlab/treeprint"
 )
 
@@ -31,7 +33,6 @@ func (c *ProvidersCommand) Run(args []string) int {
 		return 1
 	}
 
-	/*
 	configPath, err := ModulePath(cmdFlags.Args())
 	if err != nil {
 		c.Ui.Error(err.Error())
@@ -83,22 +84,30 @@ func (c *ProvidersCommand) Run(args []string) int {
 
 	// Get the state
 	env := c.Workspace()
-		state, err := b.StateMgr(env)
+	s, err := b.StateMgr(env)
 	if err != nil {
 		c.Ui.Error(fmt.Sprintf("Failed to load state: %s", err))
 		return 1
 	}
-		if err := state.RefreshState(); err != nil {
+	if err := s.RefreshState(); err != nil {
 		c.Ui.Error(fmt.Sprintf("Failed to load state: %s", err))
 		return 1
 	}
 
-		s := state.State()
-		depTree := terraform.ConfigTreeDependencies(config, s)
-		depTree.SortDescendents()
+	reqs, reqDiags := config.ProviderRequirements()
+	if reqDiags.HasErrors() {
+		c.showDiagnostics(configDiags)
+		return 1
+	}
+
+	state := s.State()
+	if state != nil {
+		stateReqs := state.ProviderRequirements()
+		reqs = reqs.Merge(stateReqs)
+	}
 
 	printRoot := treeprint.New()
-		providersCommandPopulateTreeNode(printRoot, depTree)
+	providersCommandPopulateTreeNode(printRoot, reqs)
 
 	c.Ui.Output(printRoot.String())
 
@@ -106,48 +115,25 @@ func (c *ProvidersCommand) Run(args []string) int {
 	if diags.HasErrors() {
 		return 1
 	}
-	*/
-
-	c.Ui.Output(fmt.Sprintf("terraform providers is temporarily disabled"))
 	return 0
 }
 
-func providersCommandPopulateTreeNode(node treeprint.Tree, deps *moduledeps.Module) {
-	fqns := make([]addrs.Provider, 0, len(deps.Providers))
-	for fqn := range deps.Providers {
-		fqns = append(fqns, fqn)
-	}
-
-	for _, fqn := range fqns {
-		dep := deps.Providers[fqn]
-		versionsStr := dep.Constraints.String()
+func providersCommandPopulateTreeNode(node treeprint.Tree, deps getproviders.Requirements) {
+	for fqn, dep := range deps {
+		versionsStr := getproviders.VersionConstraintsString(dep)
 		if versionsStr != "" {
 			versionsStr = " " + versionsStr
 		}
-		var reasonStr string
-		switch dep.Reason {
-		case moduledeps.ProviderDependencyInherited:
-			reasonStr = " (inherited)"
-		case moduledeps.ProviderDependencyFromState:
-			reasonStr = " (from state)"
-		}
-		node.AddNode(fmt.Sprintf("provider.%s%s%s", fqn.LegacyString(), versionsStr, reasonStr))
-	}
-
-	for _, child := range deps.Children {
-		childNode := node.AddBranch(fmt.Sprintf("module.%s", child.Name))
-		providersCommandPopulateTreeNode(childNode, child)
+		node.AddNode(fmt.Sprintf("provider[%s]%s", fqn.String(), versionsStr))
 	}
 }
 
 const providersCommandHelp = `
 Usage: terraform providers [dir]
 
-  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 across all
-  referenced modules, as an aid to understanding why particular provider
-  plugins are needed and why particular versions are selected.
+  Prints out a list of providers required by the configuration and state.
 
+  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.
 `

command/providers_test.go

@@ -9,12 +9,11 @@ import (
 )
 
 func TestProviders(t *testing.T) {
-	return
 	cwd, err := os.Getwd()
 	if err != nil {
 		t.Fatalf("err: %s", err)
 	}
-	if err := os.Chdir(testFixturePath("providers")); err != nil {
+	if err := os.Chdir(testFixturePath("providers/basic")); err != nil {
 		t.Fatalf("err: %s", err)
 	}
 	defer os.Chdir(cwd)
@@ -31,20 +30,21 @@ func TestProviders(t *testing.T) {
 		t.Fatalf("bad: %d\n\n%s", code, ui.ErrorWriter.String())
 	}
 
+	wantOutput := []string{
+		"provider[registry.terraform.io/hashicorp/foo]",
+		"provider[registry.terraform.io/hashicorp/bar]",
+		"provider[registry.terraform.io/hashicorp/baz]",
+	}
+
 	output := ui.OutputWriter.String()
-	if !strings.Contains(output, "provider.foo") {
-		t.Errorf("output missing provider.foo\n\n%s", output)
+	for _, want := range wantOutput {
+		if !strings.Contains(output, want) {
+			t.Errorf("output missing %s:\n%s", want, output)
 		}
-	if !strings.Contains(output, "provider.bar") {
-		t.Errorf("output missing provider.bar\n\n%s", output)
-	}
-	if !strings.Contains(output, "provider.baz") {
-		t.Errorf("output missing provider.baz\n\n%s", output)
 	}
 }
 
 func TestProviders_noConfigs(t *testing.T) {
-	return
 	cwd, err := os.Getwd()
 	if err != nil {
 		t.Fatalf("err: %s", err)
@@ -73,3 +73,96 @@ func TestProviders_noConfigs(t *testing.T) {
 		t.Errorf("Expected error message: %s\nGiven output: %s", expectedErrMsg, output)
 	}
 }
+
+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)
+
+	// first run init with mock provider sources to install the module
+	initUi := new(cli.MockUi)
+	providerSource, close := newMockProviderSource(t, map[string][]string{
+		"foo": {"1.0.0"},
+		"bar": {"2.0.0"},
+		"baz": {"1.2.2"},
+	})
+	defer close()
+	m := Meta{
+		testingOverrides: metaOverridesForProvider(testProvider()),
+		Ui:               initUi,
+		ProviderSource:   providerSource,
+	}
+	ic := &InitCommand{
+		Meta: m,
+	}
+	if code := ic.Run([]string{}); code != 0 {
+		t.Fatalf("init failed\n%s", initUi.ErrorWriter)
+	}
+
+	// Providers command
+	ui := new(cli.MockUi)
+	c := &ProvidersCommand{
+		Meta: Meta{
+			Ui: ui,
+		},
+	}
+
+	args := []string{}
+	if code := c.Run(args); code != 0 {
+		t.Fatalf("bad: %d\n\n%s", code, ui.ErrorWriter.String())
+	}
+
+	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
+	}
+
+	output := ui.OutputWriter.String()
+	for _, want := range wantOutput {
+		if !strings.Contains(output, want) {
+			t.Errorf("output missing %s:\n%s", want, output)
+		}
+	}
+}
+
+func TestProviders_state(t *testing.T) {
+	cwd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	if err := os.Chdir(testFixturePath("providers/state")); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	defer os.Chdir(cwd)
+
+	ui := new(cli.MockUi)
+	c := &ProvidersCommand{
+		Meta: Meta{
+			Ui: ui,
+		},
+	}
+
+	args := []string{}
+	if code := c.Run(args); code != 0 {
+		t.Fatalf("bad: %d\n\n%s", code, ui.ErrorWriter.String())
+	}
+
+	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
+		"provider[registry.terraform.io/hashicorp/baz]",       // from a resouce in state (only)
+	}
+
+	output := ui.OutputWriter.String()
+	for _, want := range wantOutput {
+		if !strings.Contains(output, want) {
+			t.Errorf("output missing %s:\n%s", want, output)
+		}
+	}
+}

command/testdata/providers/modules/child/main.tf

@@ -0,0 +1 @@
+resource "baz_resource" "baz" {}

command/testdata/providers/modules/main.tf

@@ -0,0 +1,15 @@
+terraform {
+  required_providers {
+    foo = {
+      version = "1.0"
+    }
+  }
+}
+
+provider "bar" {
+  version = "2.0.0"
+}
+
+module "child" {
+  source = "./child"
+}

command/testdata/providers/state/main.tf

@@ -0,0 +1,11 @@
+terraform {
+  required_providers {
+    foo = {
+      version = "1.0"
+    }
+  }
+}
+
+provider "bar" {
+  version = "2.0.0"
+}

command/testdata/providers/state/terraform.tfstate

@@ -0,0 +1,24 @@
+{
+    "version": 4,
+    "terraform_version": "0.13.0",
+    "serial": 1,
+    "lineage": "00bfda35-ad61-ec8d-c013-14b0320bc416",
+    "outputs": {},
+    "resources": [
+        {
+            "mode": "managed",
+            "type": "baz_instance",
+            "name": "example",
+            "provider": "provider[\"registry.terraform.io/hashicorp/baz\"]",
+            "instances": [
+                {
+                    "schema_version": 0,
+                    "attributes": {
+                        "id": "621124146446964903"
+                    },
+                    "private": "bnVsbA=="
+                }
+            ]
+        }
+    ]
+}

configs/config_test.go

@@ -125,6 +125,7 @@ func TestConfigProviderRequirements(t *testing.T) {
 	randomProvider := addrs.NewDefaultProvider("random")
 	impliedProvider := addrs.NewDefaultProvider("implied")
 	terraformProvider := addrs.NewBuiltInProvider("terraform")
+	configuredProvider := addrs.NewDefaultProvider("configured")
 
 	got, diags := cfg.ProviderRequirements()
 	assertNoDiagnostics(t, diags)
@@ -133,6 +134,7 @@ func TestConfigProviderRequirements(t *testing.T) {
 		nullProvider:       getproviders.MustParseVersionConstraints("~> 2.0.0, 2.0.1"),
 		randomProvider:     getproviders.MustParseVersionConstraints("~> 1.2.0"),
 		tlsProvider:        getproviders.MustParseVersionConstraints("~> 3.0"),
+		configuredProvider: getproviders.MustParseVersionConstraints("~> 1.4"),
 		impliedProvider:    nil,
 		happycloudProvider: nil,
 		terraformProvider:  nil,

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

@@ -26,3 +26,9 @@ module "child" {
 # registry.terraform.io/hashicorp/terraform.
 data "terraform_remote_state" "bar" {
 }
+
+# There is no provider in required_providers called "configured", so the version
+# constraint should come from this configuration block.
+provider "configured" {
+  version = "~> 1.4"
+}

website/docs/commands/providers.html.markdown

@@ -14,6 +14,9 @@ used in the current configuration.
 
 Provider dependencies are created in several different ways:
 
+* Explicit use of a `terraform.required_providers` block in configuration,
+  optionally including a version constraint.
+
 * Explicit use of a `provider` block in configuration, optionally including
   a version constraint.