Ensure absolute file paths for diagnostics

[ryanashcraft]

I've been experiencing an issue with flow-for-vscode's diagnostics where I'm receiving errors like this when clicking on an error in the "problems" view:

I've dug into this a bit, and it seems the issue is related to a bad assumption that flow status --json always returns absolute paths. I'm guessing that most flow projects, the paths are absolute. This is the case with flow-for-vscode. However, with my project, the paths are relative to the project root – without a leading ./. This causes a problem when the file is converted into a URI with vscode.Uri.file, which expects absolute paths and results in an invalid URI.

This change ensures that the file path is always absolute, leveraging the flowRoot value from flowFindDiagnostics, before converting it into a URI with vscode.Uri.file.

---

For additional context, I'm pretty confident I know what is driving this inconsistency with the output of flow status. My project is configured to treat our top-level src directory to be treated as a module root using module.system.node.resolve_dirname=src. We do this so that we can import our own modules similarly to how we import modules from node_modules. For example, importing components/AddToDashboardSelect/AddToDashboardSelect resolves to <PROJECT_ROOT>/src/components/AddToDashboardSelect/AddToDashboardSelect.

Sample output from ./node_modules/.bin/flow status --json for my project:

{
  "context": "                optionGroups={this.getOptionGroups()}",
  "descr": "tuple type",
  "type": "Blame",
  "loc": {
    "source": "src/components/AddLegendSeriesSelect/AddLegendSeriesSelect.jsx",
    "type": "SourceFile",
    "start": {
      "line": 62,
      "column": 31,
      "offset": 1694
    },
    "end": {
      "line": 62,
      "column": 52,
      "offset": 1716
    }
  },
  "path": "src/components/AddLegendSeriesSelect/AddLegendSeriesSelect.jsx",
  "line": 62,
  "endline": 62,
  "start": 31,
  "end": 52
},

Compared to flow-for-vscode:

{
  "context": "\t\tconst line = position.line;",
  "descr": "property `line`",
  "type": "Blame",
  "loc": {
    "source": "/Users/ryanashcraft/Desktop/flow-for-vscode/lib/flowCompletion.js",
    "type": "SourceFile",
    "start": {
      "line": 31,
      "column": 25,
      "offset": 720
    },
    "end": {
      "line": 31,
      "column": 28,
      "offset": 724
    }
  },
  "path": "/Users/ryanashcraft/Desktop/flow-for-vscode/lib/flowCompletion.js",
  "line": 31,
  "endline": 31,
  "start": 25,
  "end": 28
},

[facebook-github-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. In order for us to review and merge your code, please sign up at https://code.facebook.com/cla - and if you have received this in error or have any questions, please drop us a line at cla@fb.com. Thanks!

If you are contributing on behalf of someone else (eg your employer): the individual CLA is not sufficient - use https://developers.facebook.com/opensource/cla?type=company instead. Contact cla@fb.com if you have any questions.

[orta]

Looks pretty 👍 to me - can you please add a CHANGELOG entry too

[facebook-github-bot]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[ryanashcraft]

@orta updated CHANGELOG

[orta]

👍

[ryanashcraft]

Thanks @orta!

[orta]

Thanks to you for contributing @ryanashcraft