Improve install of templates from places other than `npm` registry

[piranna]

• I have reviewed the documentation
• I have searched existing issues
• I am using the latest React Native version

When trying to install a project template from other place than published as a npm package (github forks, local filesystem, local tarfile, http server...) I can't be able to do it due to several problems. Debuging them, I get to the conclussion the problem is at

react-native/local-cli/generator/templates.js

Lines 112 to 120 in 26684cf

	if (template.includes('://')) {
	// URL, e.g. git://, file://
	installPackage = template;
	templateName = template.substr(template.lastIndexOf('/') + 1);
	} else {
	// e.g 'demo'
	installPackage = 'react-native-template-' + template;
	templateName = installPackage;
	}

, not processing the template name correctly. Problems I've found in this code snippet are:

• lack of support to download a git project subpath (seems a problem in npm not supporting mono-repos)
• templateName gets not cleaned, file extension should be removed
• templateName can't be different of the package name at the template package.json file, correct name should be extracted once the template is installed
• when installed from npm, installPackage is just a concatenation of the string react-native-template- and the provided template name, not allowing to use scoped packages as templates. Provided template should be checked and splitted, and the scoped prefixed to the generated templateName

Environment

Environment:
  OS: Linux 4.13
  Node: 9.11.1
  Yarn: Not Found
  npm: 5.6.0
  Watchman: 4.9.0
  Xcode: N/A
  Android Studio: 3.1 AI-173.4697961

Packages: (wanted => installed)
  react: 16.3.1 => 16.3.1
  react-native: 0.55.2 => 0.55.2

Steps to Reproduce

Try to init a React Native project using a template from a git mono-repo, or from a local filesystem folder, or from a tarfile on the local filesystem or a web server, or from a scoped npm package.

Expected Behavior

All the provided methods should be able to correctly install the provided template.

Actual Behavior

All of them fails.

[stale]

Hey there, it looks like there has been no activity on this issue recently. Has the issue been fixed, or does it still require the community's attention? This issue may be closed if no further activity occurs. You may also label this issue as "For Discussion" or "Good first issue" and I will leave it open. Thank you for your contributions.

[piranna]

This issue still needs community's attention. Can someone review it?

[scally-grab]

Came here to +1 this issue. Template install from NPM works fine, from git repos is worse, and from the local filesystem seems nearly nonfunctional for me.

[stale]

Hey there, it looks like there has been no activity on this issue recently. Has the issue been fixed, or does it still require the community's attention? This issue may be closed if no further activity occurs. You may also label this issue as "For Discussion" or "Good first issue" and I will leave it open. Thank you for your contributions.

[piranna]

Yes, it still happens.

[piranna]

Still happening with React Native 0.57.8.