Why are we hardcoding this.covSources[0] in _maybeRemapStartColEndCol function

[Songyu-Wang]

Hello,
So I am trying to convert my v8 coverage to istanbul and got surprised that the translation is not working as expected.

Unfortunately I cannot share a repo for you to debug, so I have to debug this myself.

After loading the source,

v8-to-istanbul/lib/v8-to-istanbul.js

Line 47 in 4488d10

async load () {

[
  {
    source: CovSource {
      lines: [Array],
      eof: 736,
      shebangLength: 0,
      wrapperLength: 0
    },
    path: 'webpack://A.ts'
  },
  {
    source: CovSource {
      lines: [Array],
      eof: 1087,
      shebangLength: 0,
      wrapperLength: 0
    },
    path: 'webpack://B.ts'
  },
  {
    source: CovSource {
      lines: [Array],
      eof: 2275,
      shebangLength: 0,
      wrapperLength: 0
    },
    path: 'webpack://C.ts'
  },
  {
    source: CovSource {
      lines: [Array],
      eof: 15840,
      shebangLength: 0,
      wrapperLength: 0
    },
    path: 'webpack://D.ts'
  },
  {
    source: CovSource {
      lines: [Array],
      eof: 1884,
      shebangLength: 0,
      wrapperLength: 0
    },
    path: 'webpack://E.ts'
  },
  {
    source: CovSource {
      lines: [Array],
      eof: 11237,
      shebangLength: 0,
      wrapperLength: 0
    },
    path: 'webpack://F.ts'
  },
  {
    source: CovSource {
      lines: [Array],
      eof: 11691,
      shebangLength: 0,
      wrapperLength: 0
    },
    path: 'webpack://G.ts'
  }
]

are loaded as this.covSources

v8-to-istanbul/lib/v8-to-istanbul.js

Line 38 in 4488d10

this.covSources = []

v8-to-istanbul/lib/v8-to-istanbul.js

Line 128 in 4488d10

applyCoverage (blocks) {

When applyCoverage is called, const { startCol, endCol, path, covSource } = this._maybeRemapStartColEndCol(range, isEmptyCoverage) should give me one of the covSource above.

v8-to-istanbul/lib/v8-to-istanbul.js

Line 132 in 4488d10

const { startCol, endCol, path, covSource } = this._maybeRemapStartColEndCol(range, isEmptyCoverage)

Based on the current implementation,

 {
    source: CovSource {
      lines: [Array],
      eof: 736,
      shebangLength: 0,
      wrapperLength: 0
    },
    path: 'webpack://A.ts'
  },

v8-to-istanbul/lib/v8-to-istanbul.js

Line 212 in 4488d10

let covSource = this.covSources[0].source

will always get return regardless of the block value because it will always use the first object in the list. In my case, the functionName is from webpack://G.ts
Edit: See comment below

v8-to-istanbul/README.md

Line 20 in 4488d10

"functionName": "",

As a result, all the data are messed up...

[Songyu-Wang]

Apologies, I think I overlooked the code that matching the source
https://github.com/istanbuljs/v8-to-istanbul/blob/4488d10cc9d828c4f6fc0650b04f1909dcbadfff/lib/v8-to-istanbul.js#L230C7-L231C23

In my case, I have a mismatch between webpack://G.ts and webpack://./G.ts
and cause everything to default to this.covSources[0]

Could we add a warning whenever we default to this.covSources[0]?