command: Add state replace-provider subcommand

Terraform 0.13 will allow the installation of providers from various
sources. If a user updates their configuration to change the source of
an in-use provider (for example, if the provider namespace changes),
they will also need to update the state file accordingly.

This commit introduces a new `state replace-provider` subcommand which
supports this. All resources using the `from` provider will be updated
to use the `to` provider.

command/state_meta.go

@@ -196,3 +196,14 @@ func (c *StateMeta) collectResourceInstances(moduleAddr addrs.ModuleInstance, rs
 	}
 	return ret
 }
+
+func (c *StateMeta) lookupAllResources(state *states.State) ([]*states.Resource, tfdiags.Diagnostics) {
+	var ret []*states.Resource
+	var diags tfdiags.Diagnostics
+	for _, ms := range state.Modules {
+		for _, resource := range ms.Resources {
+			ret = append(ret, resource)
+		}
+	}
+	return ret, diags
+}

command/state_replace_provider.go

@@ -0,0 +1,198 @@
+package command
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/hashicorp/terraform/addrs"
+	"github.com/hashicorp/terraform/command/clistate"
+	"github.com/hashicorp/terraform/states"
+	"github.com/hashicorp/terraform/tfdiags"
+	"github.com/mitchellh/cli"
+)
+
+// StateReplaceProviderCommand is a Command implementation that allows users
+// to change the provider associated with existing resources. This is only
+// likely to be useful if a provider is forked or changes its fully-qualified
+// name.
+
+type StateReplaceProviderCommand struct {
+	StateMeta
+}
+
+func (c *StateReplaceProviderCommand) Run(args []string) int {
+	args = c.Meta.process(args)
+
+	var autoApprove bool
+	cmdFlags := c.Meta.defaultFlagSet("state replace-provider")
+	cmdFlags.BoolVar(&autoApprove, "auto-approve", false, "skip interactive approval of replacements")
+	cmdFlags.StringVar(&c.backupPath, "backup", "-", "backup")
+	cmdFlags.BoolVar(&c.Meta.stateLock, "lock", true, "lock states")
+	cmdFlags.DurationVar(&c.Meta.stateLockTimeout, "lock-timeout", 0, "lock timeout")
+	cmdFlags.StringVar(&c.statePath, "state", "", "path")
+	if err := cmdFlags.Parse(args); err != nil {
+		c.Ui.Error(fmt.Sprintf("Error parsing command-line flags: %s\n", err.Error()))
+		return cli.RunResultHelp
+	}
+	args = cmdFlags.Args()
+	if len(args) != 2 {
+		c.Ui.Error("Exactly two arguments expected.\n")
+		return cli.RunResultHelp
+	}
+
+	var diags tfdiags.Diagnostics
+
+	// Parse from/to arguments into providers
+	from, fromDiags := addrs.ParseProviderSourceString(args[0])
+	if fromDiags.HasErrors() {
+		diags = diags.Append(tfdiags.Sourceless(
+			tfdiags.Error,
+			fmt.Sprintf(`Invalid "from" provider %q`, args[0]),
+			fromDiags.Err().Error(),
+		))
+	}
+	to, toDiags := addrs.ParseProviderSourceString(args[1])
+	if toDiags.HasErrors() {
+		diags = diags.Append(tfdiags.Sourceless(
+			tfdiags.Error,
+			fmt.Sprintf(`Invalid "to" provider %q`, args[1]),
+			toDiags.Err().Error(),
+		))
+	}
+	if diags.HasErrors() {
+		c.showDiagnostics(diags)
+		return 1
+	}
+
+	// Initialize the state manager as configured
+	stateMgr, err := c.State()
+	if err != nil {
+		c.Ui.Error(fmt.Sprintf(errStateLoadingState, err))
+		return 1
+	}
+
+	// Acquire lock if requested
+	if c.stateLock {
+		stateLocker := clistate.NewLocker(context.Background(), c.stateLockTimeout, c.Ui, c.Colorize())
+		if err := stateLocker.Lock(stateMgr, "state-replace-provider"); err != nil {
+			c.Ui.Error(fmt.Sprintf("Error locking source state: %s", err))
+			return 1
+		}
+		defer stateLocker.Unlock(nil)
+	}
+
+	// Refresh and load state
+	if err := stateMgr.RefreshState(); err != nil {
+		c.Ui.Error(fmt.Sprintf("Failed to refresh source state: %s", err))
+		return 1
+	}
+
+	state := stateMgr.State()
+	if state == nil {
+		c.Ui.Error(fmt.Sprintf(errStateNotFound))
+		return 1
+	}
+
+	// Fetch all resources from the state
+	resources, diags := c.lookupAllResources(state)
+	if diags.HasErrors() {
+		c.showDiagnostics(diags)
+		return 1
+	}
+
+	var willReplace []*states.Resource
+
+	// Update all matching resources with new provider
+	for _, resource := range resources {
+		if resource.ProviderConfig.Provider.Equals(from) {
+			willReplace = append(willReplace, resource)
+		}
+	}
+	c.showDiagnostics(diags)
+
+	if len(willReplace) == 0 {
+		c.Ui.Output("No matching resources found.")
+		return 0
+	}
+
+	// Explain the changes
+	colorize := c.Colorize()
+	c.Ui.Output(colorize.Color(fmt.Sprintf(
+		"Terraform will replace the provider for %d resources:\n",
+		len(willReplace),
+	)))
+	for _, resource := range willReplace {
+		c.Ui.Output(colorize.Color(fmt.Sprintf("  %s", resource.Addr)))
+	}
+	c.Ui.Output("")
+	c.Ui.Output(colorize.Color(fmt.Sprintf("From provider: [bold]%s[reset]", from)))
+	c.Ui.Output(colorize.Color(fmt.Sprintf("To provider:   [bold]%s[reset]", to)))
+
+	// Confirm
+	if !autoApprove {
+		c.Ui.Output(colorize.Color(
+			"\n[bold]Do you want to make these changes?[reset]\n" +
+				"Only 'yes' will be accepted to continue.\n",
+		))
+		v, err := c.Ui.Ask(fmt.Sprintf("Enter a value:"))
+		if err != nil {
+			c.Ui.Error(fmt.Sprintf("Error asking for approval: %s", err))
+			return 1
+		}
+		if v != "yes" {
+			c.Ui.Output("Cancelled replacing providers.")
+			return 0
+		}
+	}
+
+	// Update the provider for each resource
+	for _, resource := range willReplace {
+		resource.ProviderConfig.Provider = to
+	}
+
+	// Write the updated state
+	if err := stateMgr.WriteState(state); err != nil {
+		c.Ui.Error(fmt.Sprintf(errStateRmPersist, err))
+		return 1
+	}
+	if err := stateMgr.PersistState(); err != nil {
+		c.Ui.Error(fmt.Sprintf(errStateRmPersist, err))
+		return 1
+	}
+
+	c.Ui.Output(fmt.Sprintf("\nSuccessfully replaced provider for %d resources.", len(willReplace)))
+	return 0
+}
+
+func (c *StateReplaceProviderCommand) Help() string {
+	helpText := `
+Usage: terraform state replace-provider [options] FROM_PROVIDER_FQN TO_PROVIDER_FQN
+
+  Replace provider for resources in the Terraform state.
+
+  An error will be returned if any of the resources or modules given as
+  filter addresses do not exist in the state.
+
+Options:
+
+  -auto-approve       Skip interactive approval.
+
+  -backup=PATH        Path where Terraform should write the backup for the
+                      state file. This can't be disabled. If not set, Terraform
+                      will write it to the same path as the state file with
+                      a ".backup" extension.
+
+  -lock=true          Lock the state files when locking is supported.
+
+  -lock-timeout=0s    Duration to retry a state lock.
+
+  -state=PATH         Path to the state file to update. Defaults to the configured
+                      backend, or "terraform.tfstate"
+`
+	return strings.TrimSpace(helpText)
+}
+
+func (c *StateReplaceProviderCommand) Synopsis() string {
+	return "Replace provider in the state"
+}