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

[g-chao]

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

[g-chao]

@fzxen Do you know what's intention to change this this.isWorkspaceCompatible for pnpm9? Right now, when I test it, I found out this logic could not support a empty subspace (which means a empty lockfile) when using pnpm9. So I revert the logic here.

[fzxen]

@fzxen Do you know what's intention to change this this.isWorkspaceCompatible for pnpm9? Right now, when I test it, I found out this logic could not support a empty subspace (which means a empty lockfile) when using pnpm9. So I revert the logic here.

@g-chao importers.size is always greater than 0 in pnpm lockfile v9
In non-workspace mode, the importers field of lockfilev9 is exists, but it does not in lockfilev6.

rushstack/libraries/rush-lib/src/logic/test/shrinkwrapFile/non-workspace-pnpm-lock-v9.yaml

Lines 7 to 29 in 724aa51

	importers:
	.:
	dependencies:
	'@pnpm/dependency-path':
	specifier: ^5.1.7
	version: 5.1.7
	'@pnpm/lockfile.utils':
	specifier: ^1.0.4
	version: 1.0.4
	'@rush-temp/project1':
	specifier: file:./projects/project1
	version: project1@file:projects/project1
	'@rush-temp/project2':
	specifier: file:./projects/project2
	version: project2@file:projects/project2
	'@rush-temp/project3':
	specifier: file:./projects/project3
	version: project3@file:projects/project3
	pad-left:
	specifier: 1.0.0
	version: 1.0.0

[iclanton]

This check was added in #5009. IIRC there was an explicit reason this was necessary. @fzxen?