@@ -34,10 +34,6 @@ var (
 	ErrDefaultWorkspaceNotSupported = errors.New("default workspace not supported\n" +
 		"You can create a new workspace with the \"workspace new\" command.")
 
-	// ErrOperationNotSupported is returned when an unsupported operation
-	// is detected by the configured backend.
-	ErrOperationNotSupported = errors.New("operation not supported")
-
 	// ErrWorkspacesNotSupported is an error returned when a caller attempts
 	// to perform an operation on a workspace other than "default" for a
 	// backend that doesn't support multiple workspaces.
 
@@ -5,33 +5,30 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
-	"os"
-	"runtime"
-	"strings"
-
-	"github.com/aliyun/alibaba-cloud-sdk-go/sdk/requests"
-	"github.com/aliyun/alibaba-cloud-sdk-go/sdk/responses"
-	"github.com/aliyun/alibaba-cloud-sdk-go/services/sts"
-	"github.com/aliyun/aliyun-oss-go-sdk/oss"
-	"github.com/hashicorp/terraform/backend"
-	"github.com/hashicorp/terraform/helper/schema"
-	"github.com/hashicorp/terraform/helper/validation"
-	"github.com/jmespath/go-jmespath"
-
 	"log"
 	"net/http"
+	"net/url"
+	"os"
+	"regexp"
+	"runtime"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/aliyun/alibaba-cloud-sdk-go/sdk"
 	"github.com/aliyun/alibaba-cloud-sdk-go/sdk/auth/credentials"
+	"github.com/aliyun/alibaba-cloud-sdk-go/sdk/requests"
+	"github.com/aliyun/alibaba-cloud-sdk-go/sdk/responses"
 	"github.com/aliyun/alibaba-cloud-sdk-go/services/location"
+	"github.com/aliyun/alibaba-cloud-sdk-go/services/sts"
+	"github.com/aliyun/aliyun-oss-go-sdk/oss"
 	"github.com/aliyun/aliyun-tablestore-go-sdk/tablestore"
 	"github.com/hashicorp/go-cleanhttp"
+	"github.com/hashicorp/terraform/backend"
+	"github.com/hashicorp/terraform/helper/schema"
 	"github.com/hashicorp/terraform/version"
+	"github.com/jmespath/go-jmespath"
 	"github.com/mitchellh/go-homedir"
-	"net/url"
-	"regexp"
 )
 
 // New creates a new backend for OSS remote state.
@@ -196,10 +193,23 @@ func assumeRoleSchema() *schema.Schema {
 					Description: "The permissions applied when assuming a role. You cannot use this policy to grant permissions which exceed those of the role that is being assumed.",
 				},
 				"session_expiration": {
-					Type:         schema.TypeInt,
-					Optional:     true,
-					Description:  "The time after which the established session for assuming role expires.",
-					ValidateFunc: validation.IntBetween(900, 3600),
+					Type:        schema.TypeInt,
+					Optional:    true,
+					Description: "The time after which the established session for assuming role expires.",
+					ValidateFunc: func(v interface{}, k string) ([]string, []error) {
+						min := 900
+						max := 3600
+						value, ok := v.(int)
+						if !ok {
+							return nil, []error{fmt.Errorf("expected type of %s to be int", k)}
+						}
+
+						if value < min || value > max {
+							return nil, []error{fmt.Errorf("expected %s to be in the range (%d - %d), got %d", k, min, max, v)}
+						}
+
+						return nil, nil
+					},
 				},
 			},
 		},
 
@@ -427,9 +427,8 @@ func (c *InitCommand) getProviders(config *configs.Config, state *states.State,
 	if moreDiags.HasErrors() {
 		return false, true, diags
 	}
-	stateReqs := make(getproviders.Requirements, 0)
 	if state != nil {
-		stateReqs = state.ProviderRequirements()
+		stateReqs := state.ProviderRequirements()
 		reqs = reqs.Merge(stateReqs)
 	}
 
@@ -774,16 +773,6 @@ func (c *InitCommand) getProviders(config *configs.Config, state *states.State,
 	return true, false, diags
 }
 
-func (c *InitCommand) populateProviderToReqs(reqs map[addrs.Provider][]*configs.ModuleRequirements, node *configs.ModuleRequirements) {
-	for fqn := range node.Requirements {
-		reqs[fqn] = append(reqs[fqn], node)
-	}
-
-	for _, child := range node.Children {
-		c.populateProviderToReqs(reqs, child)
-	}
-}
-
 // backendConfigOverrideBody interprets the raw values of -backend-config
 // arguments into a hcl Body that should override the backend settings given
 // in the configuration.
@@ -1030,117 +1019,6 @@ changes, we recommend adding version constraints in a required_providers block
 in your configuration, with the constraint strings suggested below.
 `
 
-const errDiscoveryServiceUnreachable = `
-[reset][bold][red]Registry service unreachable.[reset][red]
-
-This may indicate a network issue, or an issue with the requested Terraform Registry.
-`
-
-const errProviderNotFound = `
-[reset][bold][red]Provider %[1]q not available for installation.[reset][red]
-
-A provider named %[1]q could not be found in the Terraform Registry.
-
-This may result from mistyping the provider name, or the given provider may
-be a third-party provider that cannot be installed automatically.
-
-In the latter case, the plugin must be installed manually by locating and
-downloading a suitable distribution package and placing the plugin's executable
-file in the following directory:
-    %[2]s
-
-Terraform detects necessary plugins by inspecting the configuration and state.
-To view the provider versions requested by each module, run
-"terraform providers".
-`
-
-const errProviderVersionsUnsuitable = `
-[reset][bold][red]No provider %[1]q plugins meet the constraint %[2]q.[reset][red]
-
-The version constraint is derived from the "version" argument within the
-provider %[1]q block in configuration. Child modules may also apply
-provider version constraints. To view the provider versions requested by each
-module in the current configuration, run "terraform providers".
-
-To proceed, the version constraints for this provider must be relaxed by
-either adjusting or removing the "version" argument in the provider blocks
-throughout the configuration.
-`
-
-const errProviderIncompatible = `
-[reset][bold][red]No available provider %[1]q plugins are compatible with this Terraform version.[reset][red]
-
-From time to time, new Terraform major releases can change the requirements for
-plugins such that older plugins become incompatible.
-
-Terraform checked all of the plugin versions matching the given constraint:
-    %[2]s
-
-Unfortunately, none of the suitable versions are compatible with this version
-of Terraform. If you have recently upgraded Terraform, it may be necessary to
-move to a newer major release of this provider. Alternatively, if you are
-attempting to upgrade the provider to a new major version you may need to
-also upgrade Terraform to support the new version.
-
-Consult the documentation for this provider for more information on
-compatibility between provider versions and Terraform versions.
-`
-
-const errProviderInstallError = `
-[reset][bold][red]Error installing provider %[1]q: %[2]s.[reset][red]
-
-Terraform analyses the configuration and state and automatically downloads
-plugins for the providers used. However, when attempting to download this
-plugin an unexpected error occurred.
-
-This may be caused if for some reason Terraform is unable to reach the
-plugin repository. The repository may be unreachable if access is blocked
-by a firewall.
-
-If automatic installation is not possible or desirable in your environment,
-you may alternatively manually install plugins by downloading a suitable
-distribution package and placing the plugin's executable file in the
-following directory:
-    %[3]s
-`
-
-const errMissingProvidersNoInstall = `
-[reset][bold][red]Missing required providers.[reset][red]
-
-The following provider constraints are not met by the currently-installed
-provider plugins:
-
-%[1]s
-Terraform can automatically download and install plugins to meet the given
-constraints, but this step was skipped due to the use of -get-plugins=false
-and/or -plugin-dir on the command line.
-
-If automatic installation is not possible or desirable in your environment,
-you may manually install plugins by downloading a suitable distribution package
-and placing the plugin's executable file in one of the directories given in
-by -plugin-dir on the command line, or in the following directory if custom
-plugin directories are not set:
-    %[2]s
-`
-
-const errChecksumVerification = `
-[reset][bold][red]Error verifying checksum for provider %[1]q[reset][red]
-The checksum for provider distribution from the Terraform Registry
-did not match the source. This may mean that the distributed files
-were changed after this version was released to the Registry.
-`
-
-const errSignatureVerification = `
-[reset][bold][red]Error:[reset][bold] Untrusted signing key for provider %[1]q[reset]
-
-This provider package is not signed with the HashiCorp signing key, and is
-therefore incompatible with Terraform v%[2]s.
-
-A later version of Terraform may have introduced other signing keys that would
-accept this provider. Alternatively, an earlier version of this provider may
-be compatible with Terraform v%[2]s.
-`
-
 // providerProtocolTooOld is a message sent to the CLI UI if the provider's
 // supported protocol versions are too old for the user's version of terraform,
 // but a newer version of the provider is compatible.
@@ -1171,20 +1049,3 @@ Alternatively, upgrade to the latest version of Terraform for compatibility with
 
 // No version of the provider is compatible.
 const errProviderVersionIncompatible = `No compatible versions of provider %s were found.`
-
-// Logic from internal/initwd/getter.go
-var localSourcePrefixes = []string{
-	"./",
-	"../",
-	".\\",
-	"..\\",
-}
-
-func isLocalSourceAddr(addr string) bool {
-	for _, prefix := range localSourcePrefixes {
-		if strings.HasPrefix(addr, prefix) {
-			return true
-		}
-	}
-	return false
-}