cli: Fix init failure with deleted cache

The init command needs to initialize a backend, in order to access
state, in turn to derive provider requirements from state. The backend
initialization step requires building provider factories, which
previously would fail if a lockfile was present without a corresponding
local provider cache.

This commit ensures that in this situation only, errors with the
provider factories are temporarily ignored. This allows us to continue
to initialize the backend, fetch providers, and then report any errors
as necessary.

internal/command/init.go

@@ -238,7 +238,7 @@ func (c *InitCommand) Run(args []string) int {
 		// by a previous run, so we must still expect that "back" may be nil
 		// in code that follows.
 		var backDiags tfdiags.Diagnostics
-		back, backDiags = c.Backend(nil)
+		back, backDiags = c.Backend(&BackendOpts{Init: true})
 		if backDiags.HasErrors() {
 			// This is fine. We'll proceed with no backend, then.
 			back = nil

internal/command/meta.go

@@ -459,10 +459,8 @@ func (m *Meta) contextOpts() (*terraform.ContextOpts, error) {
 		opts.Providers = m.testingOverrides.Providers
 		opts.Provisioners = m.testingOverrides.Provisioners
 	} else {
-		providerFactories, err := m.providerFactories()
-		if err != nil {
-			return nil, err
-		}
+		var providerFactories map[addrs.Provider]providers.Factory
+		providerFactories, err = m.providerFactories()
 		opts.Providers = providerFactories
 		opts.Provisioners = m.provisionerFactories()
 	}
@@ -472,7 +470,7 @@ func (m *Meta) contextOpts() (*terraform.ContextOpts, error) {
 		OriginalWorkingDir: m.WorkingDir.OriginalWorkingDir(),
 	}
 
-	return &opts, nil
+	return &opts, err
 }
 
 // defaultFlagSet creates a default flag set for commands.

internal/command/meta_backend.go

@@ -112,28 +112,34 @@ func (m *Meta) Backend(opts *BackendOpts) (backend.Enhanced, tfdiags.Diagnostics
 			// indicates one or more inconsistencies between the dependency
 			// lock file and the provider plugins actually available in the
 			// local cache directory.
-			var buf bytes.Buffer
-			for addr, err := range errs {
-				fmt.Fprintf(&buf, "\n  - %s: %s", addr, err)
+			//
+			// If initialization is allowed, we ignore this error, as it may
+			// be resolved by the later step where providers are fetched.
+			if !opts.Init {
+				var buf bytes.Buffer
+				for addr, err := range errs {
+					fmt.Fprintf(&buf, "\n  - %s: %s", addr, err)
+				}
+				suggestion := "To download the plugins required for this configuration, run:\n  terraform init"
+				if m.RunningInAutomation {
+					// Don't mention "terraform init" specifically if we're running in an automation wrapper
+					suggestion = "You must install the required plugins before running Terraform operations."
+				}
+				diags = diags.Append(tfdiags.Sourceless(
+					tfdiags.Error,
+					"Required plugins are not installed",
+					fmt.Sprintf(
+						"The installed provider plugins are not consistent with the packages selected in the dependency lock file:%s\n\nTerraform uses external plugins to integrate with a variety of different infrastructure services. %s",
+						buf.String(), suggestion,
+					),
+				))
+				return nil, diags
 			}
-			suggestion := "To download the plugins required for this configuration, run:\n  terraform init"
-			if m.RunningInAutomation {
-				// Don't mention "terraform init" specifically if we're running in an automation wrapper
-				suggestion = "You must install the required plugins before running Terraform operations."
-			}
-			diags = diags.Append(tfdiags.Sourceless(
-				tfdiags.Error,
-				"Required plugins are not installed",
-				fmt.Sprintf(
-					"The installed provider plugins are not consistent with the packages selected in the dependency lock file:%s\n\nTerraform uses external plugins to integrate with a variety of different infrastructure services. %s",
-					buf.String(), suggestion,
-				),
-			))
 		} else {
 			// All other errors just get generic handling.
 			diags = diags.Append(err)
+			return nil, diags
 		}
-		return nil, diags
 	}
 	cliOpts.Validation = true
 
@@ -337,7 +343,7 @@ func (m *Meta) BackendForPlan(settings plans.Backend) (backend.Enhanced, tfdiags
 // a backend that supports local CLI operations.
 func (m *Meta) backendCLIOpts() (*backend.CLIOpts, error) {
 	contextOpts, err := m.contextOpts()
-	if err != nil {
+	if contextOpts == nil && err != nil {
 		return nil, err
 	}
 	return &backend.CLIOpts{
@@ -350,7 +356,7 @@ func (m *Meta) backendCLIOpts() (*backend.CLIOpts, error) {
 		ContextOpts:         contextOpts,
 		Input:               m.Input(),
 		RunningInAutomation: m.RunningInAutomation,
-	}, nil
+	}, err
 }
 
 // Operation initializes a new backend.Operation struct.