Code Coverage from Snowpack Mounted Directory is Broken

This repository is a repro case for a but reported against snowpack. I've tried to strip this down to it's simplest form. To reproduce the issue

> yarn install     # to install dependencies
> yarn start       # to run snowpack dev and view the rendered page successfully
> yarn test        # to run the tests and verify that 1/1 test passes
> yarn cover       # to run a coverage report and start a local server in that directory

When running the yarn cover task, browse to http://localhost:3030 to view the report. Drill into the coverage of src/example.js to see the following error in the report

Unable to lookup source: /home/jake/tmp/foo/example.js (ENOENT: no such file or directory, open '/home/jake/tmp/foo/example.js')
Error: Unable to lookup source: /home/jake/tmp/foo/example.js (ENOENT: no such file or directory, open '/home/jake/tmp/foo/example.js')
    at Context.defaultSourceLookup [as sourceFinder] (/home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/context.js:17:15)
    at Context.getSource (/home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/context.js:71:21)
    at annotateSourceCode (/home/jake/tmp/foo/node_modules/istanbul-reports/lib/html/annotator.js:213:40)
    at HtmlReport.onDetail (/home/jake/tmp/foo/node_modules/istanbul-reports/lib/html/index.js:409:33)
    at LcovReport. [as onDetail] (/home/jake/tmp/foo/node_modules/istanbul-reports/lib/lcov/index.js:28:23)
    at Visitor.value (/home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/tree.js:38:38)
    at ReportNode.visit (/home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/tree.js:88:21)
    at /home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/tree.js:92:19
    at Array.forEach ()
    at ReportNode.visit (/home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/tree.js:91:28)

Details

When using Snowpack and Web Test Runner to show code coverage, the coverage report is broken when using a snowpack mounted directory. It works fine if you run everything from the root directory.

Repro steps:

Create a plain vanilla snowpack project with
- src/index.html - a stock html layout
- src/example.js - a simple javascript module
- src/example.test.js - a simple test module
Configure snowpack to mount the /src directory as /
Configure web-test-runner as our test runner
Run the tests with the --coverage option.

Expected: Should be able to view html code coverage report Actual: coverage report could not locate source files...

Unable to lookup source: /home/jake/tmp/foo/example.js (ENOENT: no such file or directory, open '/home/jake/tmp/foo/example.js')
Error: Unable to lookup source: /home/jake/tmp/foo/example.js (ENOENT: no such file or directory, open '/home/jake/tmp/foo/example.js')
    at Context.defaultSourceLookup [as sourceFinder] (/home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/context.js:17:15)
    at Context.getSource (/home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/context.js:71:21)
    at annotateSourceCode (/home/jake/tmp/foo/node_modules/istanbul-reports/lib/html/annotator.js:213:40)
    at HtmlReport.onDetail (/home/jake/tmp/foo/node_modules/istanbul-reports/lib/html/index.js:409:33)
    at LcovReport. [as onDetail] (/home/jake/tmp/foo/node_modules/istanbul-reports/lib/lcov/index.js:28:23)
    at Visitor.value (/home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/tree.js:38:38)
    at ReportNode.visit (/home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/tree.js:88:21)
    at /home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/tree.js:92:19
    at Array.forEach ()
    at ReportNode.visit (/home/jake/tmp/foo/node_modules/istanbul-lib-report/lib/tree.js:91:28)

NOTE: the path that istanbul was trying to lookup files is missing the /src component

jakesgordon/snowpack-coverage-bug

Code Coverage from Snowpack Mounted Directory is Broken

Details