SDK's `getGenerator` function's `binaryPathsOverride` does not return the binary/library it downloaded

Bug description

SDK's getGenerators function accepts a binaryPathsOverride parameter to override the binary/library it uses. If neither a library or binary path override is given, it is supposed to download the correct thing and return the path to the thing it downloaded. But currently, if both overrides are omitted, then getGenerator downloads the correct thing, but does not return the path to the thing it downloaded.

How to reproduce

I use getGenerators like so:

import { getGenerator } from '@prisma/sdk`

const useBinary = false;
const useLibrary = false;

const prismaClientGenerator = await getGenerator({
          schemaPath: this.schemaPath,
          binaryPathsOverride: {
            queryEngine: useBinary ? "<custom-path>" : undefined
            libqueryEngineNapi: useLibrary ? "<custom-path>" : undefined
          }
        })

In this case, prismaClientGenerator.options.binaryPaths does not contain the path to the binary / library that this function downloaded. Instead, prismaClientGenerator.options.binaryPaths is { queryEngine: { darwin: undefined } }

However, if I call this function like so:

import { getGenerator } from '@prisma/sdk`

const useBinary = false;
const useLibrary = false;

const prismaClientGenerator = await getGenerator({
          schemaPath: this.schemaPath,
          binaryPathsOverride: queryEngine
            ? {
                [useBinary
                  ? 'queryEngine'
                  : 'libqueryEngineNapi']: "<custom-path>",
              }
            : undefined
        })

then all is good. It seems overriding individual properties inside binaryPathsOverride causes this problem, but setting binaryPathsOverride itself does not.

Expected behavior

prismaClientGenerator.options.binaryPaths should be:

{
  queryEngine: { darwin: "<path-to-downloaded-binary>" }
}

or

{
  libqueryEngineNapi: { darwin: "<path-to-downloaded-binary>" }
}

in both cases.

Prisma information

Not relevant

Environment & setup

Not relevant, but

• OS: macOS
• Database: Postgres
• Node.js version: v14.17.0

Prisma Version

Irrelevant, but:

@prisma/sdk's version is: 2.25.0-dev.32

Start at the @prisma/sdk getGenerator entry point and trace how binaryPathsOverride is combined with the downloaded path. Reproduce the case where both individual overrides are undefined, then verify that options.binaryPaths contains the downloaded queryEngine or libqueryEngineNapi path in the expected shape.