"No current database" error when moving to home page from schema page

[pavish]

Description

• Navigate to the schema page (/http://localhost:8000/db/<db_id>/<schema_id>/ where tables are listed.
• Click on the Mathesar icon in the breadcrumbs (It redirects to /).
• Notice an error being thrown on the console:

  Uncaught (in promise) Error: No current database
   at databases.ts:110:17
   at sync (chunk-46BDKJIK.js?v=a71937be:71:22)
   at Array.<anonymous> (chunk-46BDKJIK.js?v=a71937be:82:9)
   at Object.set (chunk-46BDKJIK.js?v=a71937be:30:35)
   at DatabasesStore.clearCurrentDatabaseId (databases.ts:96:28)
   at handleUnmount (DatabaseRoute.svelte:22:20)
   at run (chunk-WAIAKUYY.js?v=a71937be:19:10)
   at Array.forEach (<anonymous>)
   at run_all (chunk-WAIAKUYY.js?v=a71937be:25:7)
   at destroy_component (chunk-WAIAKUYY.js?v=a71937be:1672:5)
  

• The app crashes after that i.e. no other action is possible until a full reload.
• We discussed throwing this error in Implement tables.list and tables.delete RPC APIs on the schema page #3651, however, we missed testing the scenario of the unmounting of DatabaseRoute during review.

Some possible causes

• This error is related to this line and here.
• The DatabaseRoute is unmounted while visiting /, which sets databasesStore.currentDatabaseId to undefined.
• This in turn results in databasesStore.currentDatabase being undefined.
• There are two possible causes for this:
• The most possible cause:
  • The tables store uses the currentDatabase store. The tables store is initialized when visiting the schema page.
  • This keeps the currentDatabase store in use.
  • Since the Svelte stores within tables store are long living and live on the highest app context, they never get destroyed. This is by design. (Eg., currentTablesData derived store).
  • This keeps currentDatabase subscribed even when moving to the base / route.
• Another less-possible cause:
  • Svelte derived store seems to perform a sync action during unsubscribing if the store had been set a value before (i.e. inited), which forcibly syncs the currentDatabase store throwing the error since the value is undefined.

      const unsubscribers = stores_array.map((store, i) => subscribe(store, (value) => {
        values[i] = value;
        pending &= ~(1 << i);
        if (inited) {
          sync();
        }
      }, () => {
        pending |= 1 << i;
      }));
    

    Refer this line in the svelte repository.

Expected behavior

• There should be no error.