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• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/DevelopmentWorkflow.md#running-unit-tests-application.
• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

Only Angular projects support tsconfig.app.json.

What is the new behavior?

Any project using typescript will use the tsconfig.app.json if it exists (and fall back to tsconfig.json otherwise).

Motivation behind this change

It's common to have different tsconfigs to provide different types for VSCode intellisense, however sometimes these config changes should only apply to VSCode (or any editor) and not the app itself. In these cases this change allows setting editor defaults in tsconfig.json and then app defaults in tsconfig.app.json.

A good example where this might be useful is when you need to have intellisense in spec files by having a tsconfig.spec.json which needs to be referenced in tsconfig.json (solution-style tsconfig), however the app itself fails to compile with solution style configuration, so it needs a tsconfig.app.json that is not solution-style.

Alternative

The same can be achieved in user-config:

config.module.rule('ts').use('ts-loader').tap(options => {
  options.configFile = 'tsconfig.app.json'
  return options
})

config.plugin('ForkTsCheckerWebpackPlugin').tap(args => {
  args[0].typescript.configFile = 'tsconfig.app.json'
  return args
})