feat: introduce --log argument

bin/lcov-result-merger.js

@@ -42,20 +42,36 @@ const args = yargs(hideBin(process.argv)).command(
           default: [],
           description: 'Pass globs to ignore file paths',
         },
+        log: {
+          type: 'boolean',
+          default: false,
+          description:
+            'Show some additional information to the console about what the process is getting up' +
+            'to (fed to stderr).',
+        },
       });
   }
 ).argv;
 
 (async function () {
+  if (args.log) {
+    args.logger = function logger(...messages) {
+      process.stdout.write(`[lcov-result-merger] ${messages.join('\n')}\n`);
+    };
+  }
+
   const files = await fastGlob(args.pattern, {
     absolute: true,
     ignore: args.ignore,
   });
 
+  args.logger?.('Matched Files', JSON.stringify(files, null, 2));
+
   const mergeResults = await mergeCoverageReportFiles(files, args);
 
   if (args.outFile) {
     await writeFile(args.outFile, mergeResults, 'utf-8');
+    args.logger?.(`Results written to "${args.outFile}"`);
   } else {
     process.stdout.write(mergeResults + '\n');
   }

index.js

@@ -27,6 +27,7 @@ function processFile(sourceDir, data, lcov, config) {
   let currentCoverageFile = null;
 
   const lines = data.toString('utf-8').split(/\r?\n/);
+  config.logger?.(`Read ${lines.length} lines of content`);
 
   for (let i = 0; i < lines.length; i += 1) {
     const line = lines[i];
@@ -53,7 +54,15 @@ function processFile(sourceDir, data, lcov, config) {
             fullFilePathName
           );
 
+          config.logger?.(
+            `Re-writing source file path, Before: "${sourceFilePath}"`
+          );
+
           sourceFilePath = './' + rootRelPathName;
+
+          config.logger?.(
+            `Re-writing source file path, After:  "${sourceFilePath}"`
+          );
         }
 
         currentCoverageFile = lcov.addCoverageFile(sourceFilePath);
@@ -69,7 +78,10 @@ function processFile(sourceDir, data, lcov, config) {
         break;
 
       default:
-      // do nothing with not implemented prefixes
+        // do nothing with not implemented prefixes
+        config.logger?.(
+          `Ignoring unrecognized/unsupported entry (line #${i}): "${prefix}:${suffix}"`
+        );
     }
   }
 
@@ -90,6 +102,7 @@ async function mergeCoverageReportFiles(filePaths, options) {
 
   for (const filePath of filePaths) {
     const fileContent = await readFile(filePath, 'utf-8');
+    config.logger?.(`Processing "${filePath}"`);
     processFile(path.dirname(filePath), fileContent, report, config);
   }
 

lib/configuration.js

@@ -8,6 +8,9 @@
  * @property {string}   [prependPathFix]
  * @property {string}   [prepend-path-fix]
  * @property {string[]} [ignore]
+ * @property {boolean}  [log]
+ *
+ * @property {(...msg: string[]) => void} [logger]
  */
 
 module.exports = class Configuration {
@@ -17,22 +20,32 @@ module.exports = class Configuration {
   constructor(partial = {}) {
     /**
      * A glob pattern matching one or more lcov files to be merged.
+     *
      * @type {string}
      */
     this.pattern = partial.pattern;
 
     /**
      * A file to write the merged lcov to.
+     *
      * @type {string|undefined}
      */
     this.outFile = partial.outFile;
 
     /**
      * File path globs that will be ignored.
+     *
      * @type {string[]}
      */
     this.ignore = Array.isArray(partial.ignore) ? partial.ignore : [];
 
+    /**
+     * An optional logger function.
+     *
+     * @type {((...msg: string[]) => void) | undefined}
+     */
+    this.logger = partial.logger;
+
     /**
      * Modify source file paths to be relative to the working directory that
      * the merge operation was run in.