don't add state to the validate context

The validate command should work with the configuration, but when
validate was run at the start of a plan or apply command the state was
inserted in preparation for the next walk. This could lead to errors
when the resource schemas had changes and the state could not be
upgraded or decoded.

backend/local/backend_local.go

@@ -72,6 +72,13 @@ func (b *Local) context(op *backend.Operation) (*terraform.Context, *configload.
 	log.Printf("[TRACE] backend/local: retrieving local state snapshot for workspace %q", op.Workspace)
 	opts.State = s.State()
 
+	// Prepare a separate opts and context for validation, which doesn't use
+	// any state ensuring that we only validate the config, since evaluation
+	// will automatically reference the state when available.
+	validateOpts := opts
+	validateOpts.State = nil
+	var validateCtx *terraform.Context
+
 	var tfCtx *terraform.Context
 	var ctxDiags tfdiags.Diagnostics
 	var configSnap *configload.Snapshot
@@ -89,9 +96,18 @@ func (b *Local) context(op *backend.Operation) (*terraform.Context, *configload.
 		// Write sources into the cache of the main loader so that they are
 		// available if we need to generate diagnostic message snippets.
 		op.ConfigLoader.ImportSourcesFromSnapshot(configSnap)
+
+		// create a validation context with no state
+		validateCtx, _, _ = b.contextFromPlanFile(op.PlanFile, validateOpts, stateMeta)
+		// diags from here will be caught above
+
 	} else {
 		log.Printf("[TRACE] backend/local: building context for current working directory")
 		tfCtx, configSnap, ctxDiags = b.contextDirect(op, opts)
+
+		// create a validation context with no state
+		validateCtx, _, _ = b.contextDirect(op, validateOpts)
+		// diags from here will be caught above
 	}
 	diags = diags.Append(ctxDiags)
 	if diags.HasErrors() {
@@ -117,7 +133,7 @@ func (b *Local) context(op *backend.Operation) (*terraform.Context, *configload.
 		// If validation is enabled, validate
 		if b.OpValidation {
 			log.Printf("[TRACE] backend/local: running validation operation")
-			validateDiags := tfCtx.Validate()
+			validateDiags := validateCtx.Validate()
 			diags = diags.Append(validateDiags)
 		}
 	}