Merging v8 coverage and istanbul coverage gives NaN

[dmail]

Hell there,

I am merging two coverages: first come from v8 and was converted to istanbul format, second from istanbul itself.

When I merge the two with the following code, I end up with incorrect data

const { createCoverageMap } = require("istanbul-lib-coverage")

const istanbulCoverageMap = createCoverageMap()
istanbulCoverageMap.merge(coverageFromIstanbul)
istanbulCoverageMap.merge(coverageFromV8ConvertedToIstanbul)

const mergeResult = {}
const coverageMapData = istanbulCoverageMap.toJSON()
Object.keys(coverageMapData).forEach((key) => {
  mergeResult[key] = coverageMapData[key].toJSON()
})

coverageFromIstanbul

{
  "./test/coverage/coverage-universal/file.js": {
    "path": "./test/coverage/coverage-universal/file.js",
    "statementMap": {
      "0": {
        "start": {
          "line": 2,
          "column": 0
        },
        "end": {
          "line": 8,
          "column": 1
        }
      },
      "1": {
        "start": {
          "line": 3,
          "column": 2
        },
        "end": {
          "line": 3,
          "column": 24
        }
      },
      "2": {
        "start": {
          "line": 4,
          "column": 7
        },
        "end": {
          "line": 8,
          "column": 1
        }
      },
      "3": {
        "start": {
          "line": 5,
          "column": 2
        },
        "end": {
          "line": 5,
          "column": 21
        }
      },
      "4": {
        "start": {
          "line": 7,
          "column": 2
        },
        "end": {
          "line": 7,
          "column": 22
        }
      }
    },
    "fnMap": {},
    "branchMap": {
      "0": {
        "loc": {
          "start": {
            "line": 2,
            "column": 0
          },
          "end": {
            "line": 8,
            "column": 1
          }
        },
        "type": "if",
        "locations": [
          {
            "start": {
              "line": 2,
              "column": 0
            },
            "end": {
              "line": 8,
              "column": 1
            }
          },
          {
            "start": {
              "line": 2,
              "column": 0
            },
            "end": {
              "line": 8,
              "column": 1
            }
          }
        ],
        "line": 2
      },
      "1": {
        "loc": {
          "start": {
            "line": 4,
            "column": 7
          },
          "end": {
            "line": 8,
            "column": 1
          }
        },
        "type": "if",
        "locations": [
          {
            "start": {
              "line": 4,
              "column": 7
            },
            "end": {
              "line": 8,
              "column": 1
            }
          },
          {
            "start": {
              "line": 4,
              "column": 7
            },
            "end": {
              "line": 8,
              "column": 1
            }
          }
        ],
        "line": 4
      }
    },
    "s": {
      "0": 1,
      "1": 1,
      "2": 0,
      "3": 0,
      "4": 0
    },
    "f": {},
    "b": {
      "0": [
        1,
        0
      ],
      "1": [
        0,
        0
      ]
    },
    "_coverageSchema": "1a1c01bbd47fc00a2c39e90264f33305004495a9",
    "hash": "499a0b791cd32d6c8667bf5875758fd5f3ec4ff0"
  }
}

coverageFromV8ConvertedToIstanbul

{
  "./test/coverage/coverage-universal/file.js": {
    "path": "./test/coverage/coverage-universal/file.js",
    "all": false,
    "statementMap": {
      "0": {
        "start": {
          "line": 1,
          "column": 0
        },
        "end": {
          "line": 1,
          "column": 30
        }
      },
      "1": {
        "start": {
          "line": 2,
          "column": 0
        },
        "end": {
          "line": 2,
          "column": 33
        }
      },
      "2": {
        "start": {
          "line": 3,
          "column": 0
        },
        "end": {
          "line": 3,
          "column": 24
        }
      },
      "3": {
        "start": {
          "line": 4,
          "column": 0
        },
        "end": {
          "line": 4,
          "column": 41
        }
      },
      "4": {
        "start": {
          "line": 5,
          "column": 0
        },
        "end": {
          "line": 5,
          "column": 21
        }
      },
      "5": {
        "start": {
          "line": 6,
          "column": 0
        },
        "end": {
          "line": 6,
          "column": 8
        }
      },
      "6": {
        "start": {
          "line": 7,
          "column": 0
        },
        "end": {
          "line": 7,
          "column": 22
        }
      },
      "7": {
        "start": {
          "line": 8,
          "column": 0
        },
        "end": {
          "line": 8,
          "column": 1
        }
      }
    },
    "s": {
      "0": 1,
      "1": 1,
      "2": 0,
      "3": 1,
      "4": 1,
      "5": 1,
      "6": 0,
      "7": 0
    },
    "branchMap": {
      "0": {
        "type": "branch",
        "line": 1,
        "loc": {
          "start": {
            "line": 1,
            "column": 0
          },
          "end": {
            "line": 8,
            "column": 1
          }
        },
        "locations": [
          {
            "start": {
              "line": 1,
              "column": 0
            },
            "end": {
              "line": 8,
              "column": 1
            }
          }
        ]
      },
      "1": {
        "type": "branch",
        "line": 2,
        "loc": {
          "start": {
            "line": 2,
            "column": 32
          },
          "end": {
            "line": 4,
            "column": 1
          }
        },
        "locations": [
          {
            "start": {
              "line": 2,
              "column": 32
            },
            "end": {
              "line": 4,
              "column": 1
            }
          }
        ]
      },
      "2": {
        "type": "branch",
        "line": 6,
        "loc": {
          "start": {
            "line": 6,
            "column": 1
          },
          "end": {
            "line": 8,
            "column": 1
          }
        },
        "locations": [
          {
            "start": {
              "line": 6,
              "column": 1
            },
            "end": {
              "line": 8,
              "column": 1
            }
          }
        ]
      }
    },
    "b": {
      "0": [
        1
      ],
      "1": [
        0
      ],
      "2": [
        0
      ]
    },
    "fnMap": {},
    "f": {}
  }
}

mergeResult

{
  "./test/coverage/coverage-universal/file.js": {
    "path": "./test/coverage/coverage-universal/file.js",
    "statementMap": {
      "0": {
        "start": {
          "line": 2,
          "column": 0
        },
        "end": {
          "line": 8,
          "column": 1
        }
      },
      "1": {
        "start": {
          "line": 3,
          "column": 2
        },
        "end": {
          "line": 3,
          "column": 24
        }
      },
      "2": {
        "start": {
          "line": 4,
          "column": 7
        },
        "end": {
          "line": 8,
          "column": 1
        }
      },
      "3": {
        "start": {
          "line": 5,
          "column": 2
        },
        "end": {
          "line": 5,
          "column": 21
        }
      },
      "4": {
        "start": {
          "line": 7,
          "column": 2
        },
        "end": {
          "line": 7,
          "column": 22
        }
      }
    },
    "fnMap": {},
    "branchMap": {
      "0": {
        "loc": {
          "start": {
            "line": 2,
            "column": 0
          },
          "end": {
            "line": 8,
            "column": 1
          }
        },
        "type": "if",
        "locations": [
          {
            "start": {
              "line": 2,
              "column": 0
            },
            "end": {
              "line": 8,
              "column": 1
            }
          },
          {
            "start": {
              "line": 2,
              "column": 0
            },
            "end": {
              "line": 8,
              "column": 1
            }
          }
        ],
        "line": 2
      },
      "1": {
        "loc": {
          "start": {
            "line": 4,
            "column": 7
          },
          "end": {
            "line": 8,
            "column": 1
          }
        },
        "type": "if",
        "locations": [
          {
            "start": {
              "line": 4,
              "column": 7
            },
            "end": {
              "line": 8,
              "column": 1
            }
          },
          {
            "start": {
              "line": 4,
              "column": 7
            },
            "end": {
              "line": 8,
              "column": 1
            }
          }
        ],
        "line": 4
      }
    },
    "s": {
      "0": 2,
      "1": 2,
      "2": 0,
      "3": 1,
      "4": 1,
      "5": NaN,
      "6": NaN,
      "7": NaN
    },
    "f": {},
    "b": {
      "0": [
        2,
        NaN
      ],
      "1": [
        0,
        NaN
      ],
      "2": [
        0
      ]
    },
    "_coverageSchema": "1a1c01bbd47fc00a2c39e90264f33305004495a9",
    "hash": "499a0b791cd32d6c8667bf5875758fd5f3ec4ff0"
  }
}

The v8 coverage comes from executing the file on Node.js with NODE_V8_COVERAGE enabled.
The istanbul coverage comes from executing a file instrumented by istanbul on Firefox.

The file source code is here

if (typeof window === "object") {
  console.log("browser")
} else if (typeof process === "object") {
  console.log("node")
} else {
  console.log("other")
}