fix: Ensure identity source map has the same number of fields as the …

…combined source map (#122)

* fix: source map should have the same number of optional fields
* fix

src/index.ts

@@ -182,14 +182,20 @@ export default function istanbulPlugin(opts: IstanbulPluginOptions = {}): Plugin
       const filename = resolveFilename(id);
 
       if (testExclude.shouldInstrument(filename)) {
-        // Create a source map to combine with the source map of previous plugins
-        instrumenter.instrumentSync(srcCode, filename, createIdentitySourceMap(filename, srcCode))
+        // Instrument code using the combined source map of previous plugins
+        const combinedSourceMap = sanitizeSourceMap(this.getCombinedSourcemap());
+        const code = instrumenter.instrumentSync(srcCode, filename, combinedSourceMap);
+
+        // Create an identity source map with the same number of fields as the combined source map
+        const identitySourceMap = sanitizeSourceMap(createIdentitySourceMap(filename, srcCode, {
+          file: combinedSourceMap.file,
+          sourceRoot: combinedSourceMap.sourceRoot
+        }));
+
+        // Create a result source map to combine with the source maps of previous plugins
+        instrumenter.instrumentSync(srcCode, filename, identitySourceMap);
         const map = instrumenter.lastSourceMap();
 
-        // Instrument code using the source map of previous plugins
-        const sourceMap = sanitizeSourceMap(this.getCombinedSourcemap());
-        const code = instrumenter.instrumentSync(srcCode, filename, sourceMap);
-
         // Required to cast to correct mapping value
         return { code, map } as TransformResult;
       }

src/source-map.ts

@@ -1,9 +1,10 @@
 import * as espree from 'espree'
-import {SourceMapGenerator} from 'source-map'
+import {SourceMapGenerator, StartOfSourceMap} from 'source-map'
 
 
-export function createIdentitySourceMap(file: string, source: string) {
-    const gen = new SourceMapGenerator();
+// Create a source map which always maps to the same line and column
+export function createIdentitySourceMap(file: string, source: string, option: StartOfSourceMap) {
+    const gen = new SourceMapGenerator(option);
     const tokens = espree.tokenize(source, { loc: true, ecmaVersion: 'latest' });
 
     tokens.forEach((token: any) => {