Don't use glob with --project option

[ajafff]

PR checklist

• Addresses an existing issue: Remove duplicate fs.readFileSync call #2584, Misleading error for file not in project #2208
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

Consistently uses absolute paths when dealing with ts.Program.
Don't use glob to find files, look them up in ts.Program instead.
Don't read files from disk, because they are already available as ts.SourceFile.
Fixes: #2584

Provide a better error message if a specified file is not part of the project.
Fixes: #2208

Is there anything you'd like reviewers to focus on?

Linter should get a new method lintFile or lintSourceFile. That can be done afterwards.

CHANGELOG.md entry:

[bugfix] better error message for files not contained in the project
[enhancement] avoid duplicate IO when using --project option
[deprecation] Linting non-existent files outputs a warning. This will be an error in TSLint 6.

[adidahiya]

The error for files not in the project is also thrown for non-existant files

How do you get to this state? By supplying a nonexistent filepath in "files" in tsconfig.json?

does not match the behavior without --project because glob simply ignores files that don't exist. -> throw an error there, too?

Yeah, I think I'd prefer this approach. Sounds like a serious misconfiguration of the linter if this happens.

[adidahiya]

this is a little tricky; can you leave some comments to make this easier to follow? how do special characters in the pattern affect the logic?

[ajafff]

Given a project that only includes index.ts.
If you run tslint -p . '*.js' '*.ts' you only lint index.ts. *.js doesn't match anything but is ignored because it's a glob pattern ("has magic").
On the other hand if you run tslint -p . index.ts test/index.ts you get an error because test/index.ts is not in the project. That's because it doesn't have magic. With the current implementation it doesn't even matter if the file exists.

[adidahiya]

That makes sense; I meant to say -- can you leave a code comment

[adidahiya]

I think a changelog entry would be useful too, especially for the #2208 fix. Also we could mention potential performance improvements since we're not doing redundant file reads?

[ajafff]

The error for files not in the project is also thrown for non-existant files

How do you get to this state? By supplying a nonexistent filepath in "files" in tsconfig.json?

You can still pass arbitrary file names as arguments to the CLI. For a project that contains only index.ts you can execute tslint -p . index.ts foo.ts bar.ts
Before this PR those file names were handled as glob patterns. glob only returned the files that actually exist so we would never show an error about a file that doesn't exist.
Now throw an error for files that exist, but are not included in the project as well as files that do not exist.

[ajafff]

RE: throwing error on non-existant files
I can implement this for both branches, with --project and without. But isn't that a bit too breaking? How about printing a warning now and throwing an error in the next major version?

[adidahiya]

How about printing a warning now and throwing an error in the next major version?

yeah, that seems reasonable 👍

[ajafff]

@adidahiya updated the PR description to add changelog entries, added warnings for non-existent files with and without --project and added tests.