Make "vcpkg install --only-downloads" compatible with asset caching

[mokh-in]

Is your feature request related to a problem? Please describe.

In certain scenarios, fetching assets (of already built binaries) is needed. The assets are cached and supposed to be fetched with an external tool (using x-script).

When running vcpkg install --only-downloads passing --x-asset-sources=clear;x-script,C:\python\python.exe C:\script\vcpkg-asset-provider.py {url} {sha512} {dst};x-block-origin, the execution fails with the following error:

error : Missing <asset_name> and downloads are blocked by x-block-origin

This indicates that --only-downloads doesn't respect asset caching.

Proposed solution

Make vcpkg install --only-downloads plays nicely with asset caching.

Describe alternatives you've considered

An alternative is to remove x-block-origin. However, this would mean that vcpkg.exe bypasses the asset cache and go to the internet to fetch the assets.

Additional context

No response

[LilyWangLL]

error : Missing <asset_name> and downloads are blocked by x-block-origin

If you complete the parameters <template> in the command, will it still report the same error?

[mokh-in]

It will. The value of <template> parameter is something like:
C:\python\python.exe C:\script\vcpkg-asset-provider.py {url} {sha512} {dst}