fix!: consistently resolve paths to absolute form (#72)

BREAKING CHANGE: paths are now consistently absolute.

.github/release-please.yml

@@ -0,0 +1,2 @@
+releaseType: node
+handleGHRelease: true

lib/v8-to-istanbul.js

@@ -1,7 +1,6 @@
-const { isAbsolute, relativeTo } = require('./pathutils')
 const assert = require('assert')
 const convertSourceMap = require('convert-source-map')
-const { dirname, join } = require('path')
+const { dirname, isAbsolute, join, resolve } = require('path')
 const CovBranch = require('./branch')
 const CovFunction = require('./function')
 const CovSource = require('./source')
@@ -46,13 +45,7 @@ module.exports = class V8ToIstanbul {
         console.warn('v8-to-istanbul: source-mappings from one to many files not yet supported')
         this.source = new CovSource(rawSource, this.wrapperLength)
       } else {
-        if (rawSourceMap.sourcemap.sourceRoot && isAbsolute(rawSourceMap.sourcemap.sourceRoot)) {
-          // TODO: we should also make source-root work with relative paths, but this needs
-          // to be combined with the relativeTo logic which takes into account process.cwd().
-          this.path = join(rawSourceMap.sourcemap.sourceRoot.replace('file://', ''), rawSourceMap.sourcemap.sources[0].replace('file://', ''))
-        } else {
-          this.path = relativeTo(rawSourceMap.sourcemap.sources[0].replace('file://', ''), this.path)
-        }
+        this._rewritePath(rawSourceMap)
         this.sourceMap = await new SourceMapConsumer(rawSourceMap.sourcemap)
 
         let originalRawSource
@@ -70,6 +63,18 @@ module.exports = class V8ToIstanbul {
     }
   }
 
+  _rewritePath (rawSourceMap) {
+    const sourceRoot = rawSourceMap.sourcemap.sourceRoot ? rawSourceMap.sourcemap.sourceRoot.replace('file://', '') : ''
+    const sourcePath = rawSourceMap.sourcemap.sources[0].replace('file://', '')
+    const candidatePath = join(sourceRoot, sourcePath)
+
+    if (isAbsolute(candidatePath)) {
+      this.path = candidatePath
+    } else {
+      this.path = resolve(dirname(this.path), sourcePath)
+    }
+  }
+
   applyCoverage (blocks) {
     blocks.forEach(block => {
       block.ranges.forEach((range, i) => {