[rush-lib] Fix an bug when using pnpm 9, where a subspace is empty, the rush install fails

[g-chao]

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Summary

When using PNPM 9, if a subspace is empty. The rush install will throw follow error: The shrinkwrap file has not been updated to support workspaces. Run "rush update --full" to update the shrinkwrap file. However, after rush update --full, then rush install, the error still there.

This is due to, the isWorkspaceCompatible logic does not consider the empty lockfile case.

Here is the current logic:

this.isWorkspaceCompatible =
  this.shrinkwrapFileMajorVersion >= ShrinkwrapFileMajorVersion.V9
    ? this.importers.size > 1
    : this.importers.size > 0;

In a empty lockfile, the importers.size = 1, so I think we will need to change this logic to this.isWorkspaceCompatible = this.importers.size > 0

How it was tested

Manually tested with rush repo locally.

Impacted documentation

N/A