fix: no wrapperLength for empty coverage

lib/v8-to-istanbul.js

@@ -128,12 +128,13 @@ module.exports = class V8ToIstanbul {
   applyCoverage (blocks) {
     blocks.forEach(block => {
       block.ranges.forEach((range, i) => {
-        const { startCol, endCol, path, covSource } = this._maybeRemapStartColEndCol(range)
+        const isEmptyCoverage = block.functionName === '(empty-report)'
+        const { startCol, endCol, path, covSource } = this._maybeRemapStartColEndCol(range, isEmptyCoverage)
         if (this.excludePath(path)) {
           return
         }
         let lines
-        if (block.functionName === '(empty-report)') {
+        if (isEmptyCoverage) {
           // (empty-report), this will result in a report that has all lines zeroed out.
           lines = covSource.lines.filter((line) => {
             line.count = 0
@@ -207,15 +208,17 @@ module.exports = class V8ToIstanbul {
     })
   }
 
-  _maybeRemapStartColEndCol (range) {
+  _maybeRemapStartColEndCol (range, isEmptyCoverage) {
     let covSource = this.covSources[0].source
-    let startCol = Math.max(0, range.startOffset - covSource.wrapperLength)
-    let endCol = Math.min(covSource.eof, range.endOffset - covSource.wrapperLength)
+    const covSourceWrapperLength = isEmptyCoverage ? 0 : covSource.wrapperLength
+    let startCol = Math.max(0, range.startOffset - covSourceWrapperLength)
+    let endCol = Math.min(covSource.eof, range.endOffset - covSourceWrapperLength)
     let path = this.path
 
     if (this.sourceMap) {
-      startCol = Math.max(0, range.startOffset - this.sourceTranspiled.wrapperLength)
-      endCol = Math.min(this.sourceTranspiled.eof, range.endOffset - this.sourceTranspiled.wrapperLength)
+      const sourceTranspiledWrapperLength = isEmptyCoverage ? 0 : this.sourceTranspiled.wrapperLength
+      startCol = Math.max(0, range.startOffset - sourceTranspiledWrapperLength)
+      endCol = Math.min(this.sourceTranspiled.eof, range.endOffset - sourceTranspiledWrapperLength)
 
       const { startLine, relStartCol, endLine, relEndCol, source } = this.sourceTranspiled.offsetToOriginalRelative(
         this.sourceMap,

test/v8-to-istanbul.js

@@ -233,6 +233,42 @@ ${'//'}${'#'} sourceMappingURL=data:application/json;base64,${base64Sourcemap}
     assert(v8ToIstanbul.sourceMap !== undefined)
   })
 
+  /*
+   * Empty coverages should not cause negative end columns when
+   * wrapperLength is used.
+   */
+  it('empty coverage with custom wrapperLength', async () => {
+    const filename = require.resolve('./fixtures/scripts/uncovered.js')
+    const fileSize = lstatSync(filename).size
+    const v8ToIstanbul = new V8ToIstanbul(filename, fileSize * 2)
+
+    await v8ToIstanbul.load()
+    v8ToIstanbul.applyCoverage([{
+      functionName: '(empty-report)',
+      ranges: [{
+        startOffset: 0,
+        endOffset: fileSize,
+        count: 0
+      }],
+      isBlockCoverage: true
+    }])
+
+    const { fnMap, branchMap } = v8ToIstanbul.toIstanbul()[filename]
+
+    Object.values(fnMap).forEach(fn => {
+      fn.decl.end.column.should.above(0)
+      fn.loc.end.column.should.above(0)
+    })
+
+    Object.values(branchMap).forEach(branch => {
+      branch.loc.end.column.should.above(0)
+
+      branch.locations.forEach(location => {
+        location.end.column.should.above(0)
+      })
+    })
+  })
+
   it('empty coverage marks all lines uncovered', async () => {
     const filename = require.resolve('./fixtures/scripts/uncovered.js')
     const v8ToIstanbul = new V8ToIstanbul(filename)