Multi-project configuration doesn't type check files not included in any project

[ark120202]

What code were you trying to parse?

[1].forEach(value => value + 1);

What did you expect to happen?

No warnings

What actually happened?

A warning from @typescript-eslint/restrict-plus-operands rule.

After a bit of debugging I found out that type checker returned any type for the value node. It happened because project didn't contain a reference to package's tsconfig file, so this file was linted in a context of an inferred project.

I've tried to reproduce it in an isolated environment and looks like it works correctly if there is only one project.

UPD: After reading source it makes sense that it can't do the same thing it does with a single config, but falling back to the same program used for non-type-checked rules should also make rules handle it like it does without any project specified - throw an error.

Versions

package	version
@typescript-eslint/typescript-estree	1.12.0
TypeScript	3.5.3
node	12.1.0
npm	6.9.0

[bradzacher]

this is due to the same reason that the plugin is slow when you don't include all files within a tsconfig. It essentially handles it by fudging a lot.

The parser doesn't have a context of partially typechecked or not per file, it just reports that every file has either been fully typechecked (i.e. project is provided), or it's not.

We're planning on fixing this by throwing hard errors if the file isn't within the specified project (which is the same thing tslint did).