Minor cleanups to initialiseDehydration (#29261)

* dehydration: fix documentation

* initialiseDehydration: improve name

... to make it clearer that it does nothing if dehydration is disabled

* initialiseDehydration: remove dependency on MatrixClientPeg

We're trying to move away from relying on `MatrixClientPeg` everywhere, and
this is a particularly easy win.

src/MatrixClientPeg.ts

@@ -41,7 +41,7 @@ import PlatformPeg from "./PlatformPeg";
 import { formatList } from "./utils/FormattingUtils";
 import SdkConfig from "./SdkConfig";
 import { setDeviceIsolationMode } from "./settings/controllers/DeviceIsolationModeController.ts";
-import { initialiseDehydration } from "./utils/device/dehydration";
+import { initialiseDehydrationIfEnabled } from "./utils/device/dehydration";
 
 export interface IMatrixClientCreds {
     homeserverUrl: string;
@@ -347,7 +347,7 @@ class MatrixClientPegClass implements IMatrixClientPeg {
         // is a new login, we will start dehydration after Secret Storage is
         // unlocked.
         try {
-            await initialiseDehydration({ onlyIfKeyCached: true, rehydrate: false }, this.matrixClient);
+            await initialiseDehydrationIfEnabled(this.matrixClient, { onlyIfKeyCached: true, rehydrate: false });
         } catch (e) {
             // We may get an error dehydrating, such as if cross-signing and
             // SSSS are not set up yet.  Just log the error and continue.

src/async-components/views/dialogs/security/CreateSecretStorageDialog.tsx

@@ -37,7 +37,7 @@ import Spinner from "../../../../components/views/elements/Spinner";
 import InteractiveAuthDialog from "../../../../components/views/dialogs/InteractiveAuthDialog";
 import { type IValidationResult } from "../../../../components/views/elements/Validation";
 import PassphraseConfirmField from "../../../../components/views/auth/PassphraseConfirmField";
-import { initialiseDehydration } from "../../../../utils/device/dehydration";
+import { initialiseDehydrationIfEnabled } from "../../../../utils/device/dehydration";
 
 // I made a mistake while converting this and it has to be fixed!
 enum Phase {
@@ -273,7 +273,7 @@ export default class CreateSecretStorageDialog extends React.PureComponent<IProp
                     setupNewKeyBackup: !backupInfo,
                 });
             }
-            await initialiseDehydration({ createNewKey: true });
+            await initialiseDehydrationIfEnabled(cli, { createNewKey: true });
 
             this.setState({
                 phase: Phase.Stored,

src/stores/SetupEncryptionStore.ts

@@ -20,7 +20,7 @@ import { type Device, type SecretStorage } from "matrix-js-sdk/src/matrix";
 import { MatrixClientPeg } from "../MatrixClientPeg";
 import { AccessCancelledError, accessSecretStorage } from "../SecurityManager";
 import { asyncSome } from "../utils/arrays";
-import { initialiseDehydration } from "../utils/device/dehydration";
+import { initialiseDehydrationIfEnabled } from "../utils/device/dehydration";
 
 export enum Phase {
     Loading = 0,
@@ -149,7 +149,7 @@ export class SetupEncryptionStore extends EventEmitter {
                     );
                     resolve();
 
-                    await initialiseDehydration();
+                    await initialiseDehydrationIfEnabled(cli);
 
                     if (backupInfo) {
                         await cli.getCrypto()?.loadSessionBackupPrivateKeyFromSecretStorage();

src/utils/device/dehydration.ts

@@ -10,7 +10,6 @@ import { logger } from "matrix-js-sdk/src/logger";
 import { type CryptoApi, type StartDehydrationOpts } from "matrix-js-sdk/src/crypto-api";
 
 import type { MatrixClient } from "matrix-js-sdk/src/matrix";
-import { MatrixClientPeg } from "../../MatrixClientPeg";
 
 /**
  * Check if device dehydration is enabled.
@@ -38,11 +37,13 @@ async function deviceDehydrationEnabled(client: MatrixClient, crypto: CryptoApi
  * the configuration), rehydrate a device (if available) and create
  * a new dehydrated device.
  *
- * @param createNewKey: force a new dehydration key to be created, even if one
+ * @param client - MatrixClient to use for the operation
- *   already exists.  This is used when we reset secret storage.
+ * @param opts - options for the startDehydration operation, if one is performed.
  */
-export async function initialiseDehydration(opts: StartDehydrationOpts = {}, client?: MatrixClient): Promise<void> {
+export async function initialiseDehydrationIfEnabled(
-    client = client || MatrixClientPeg.safeGet();
+    client: MatrixClient,
+    opts: StartDehydrationOpts = {},
+): Promise<void> {
     const crypto = client.getCrypto();
     if (await deviceDehydrationEnabled(client, crypto)) {
         logger.log("Device dehydration enabled");