Validation for tns update before we execute it

[dtopuzov]

Tell us about the problem

Create project with 4.1.0
Run tns update @rc
This is invalid (it should be tns update rc).
It try to upgrade and roll back to original since @rc is invalid.
Can we validate before even try to update?

Which platform(s) does your issue occur on?

Both

Please provide the following version numbers that your issue occurs with:

• CLI: 4.1.0
• Cross-platform modules: 4.1.0
• Runtime(s): 4.1.0
• Plugin(s): No

[janoshrubos]

This has been implemented since this issue was created.
The CLI checks the version before update and throws error if the version is incorrect: Could not update the project! Reason is: Unable to execute update as package @nativescript/core does not have version/tag @rc. Please enter valid version or npm tag.

cc: @rigor789

[rigor789]

@janoshrubos I think the message is correct - however it's shown after the backup has been created/restored

nativescript-cli/lib/controllers/update-controller.ts

Lines 107 to 116 in 6de0c3e

	} catch (error) {
	this.restoreBackup(
	UpdateController.folders,
	backupDir,
	projectData.projectDir
	);
	this.$logger.error(
	`${UpdateController.updateFailMessage} Reason is: ${error.message}`
	);
	}

We could perhaps do the checks earlier in the call - before the project is cleaned/backed up.