fix(tstest-logging): Improve log file handling with log rotation and diff reporting

ts/tstest.logging.ts

@@ -37,7 +37,7 @@ export interface TestSummary {
 }
 
 export class TsTestLogger {
-  private options: LogOptions;
+  public readonly options: LogOptions;
   private startTime: number;
   private fileResults: TestFileResult[] = [];
   private currentFileResult: TestFileResult | null = null;
@@ -247,6 +247,36 @@ export class TsTestLogger {
       this.log(this.format(`   Summary: ${passed}/${total} ${status}`, color));
     }
     
+    // If using --logfile, handle error copy and diff detection
+    if (this.options.logFile && this.currentTestLogFile) {
+      try {
+        const logContent = fs.readFileSync(this.currentTestLogFile, 'utf-8');
+        const logDir = path.dirname(this.currentTestLogFile);
+        const logBasename = path.basename(this.currentTestLogFile);
+        
+        // Create error copy if there were failures
+        if (failed > 0) {
+          const errorLogPath = path.join(logDir, `00err_${logBasename}`);
+          fs.writeFileSync(errorLogPath, logContent);
+        }
+        
+        // Check for previous version and create diff if changed
+        const previousLogPath = path.join(logDir, 'previous', logBasename);
+        if (fs.existsSync(previousLogPath)) {
+          const previousContent = fs.readFileSync(previousLogPath, 'utf-8');
+          
+          // Simple check if content differs
+          if (previousContent !== logContent) {
+            const diffLogPath = path.join(logDir, `00diff_${logBasename}`);
+            const diffContent = this.createDiff(previousContent, logContent, logBasename);
+            fs.writeFileSync(diffLogPath, diffContent);
+          }
+        }
+      } catch (error) {
+        // Silently fail to avoid disrupting the test run
+      }
+    }
+    
     // Clear the current test log file reference only if using --logfile
     if (this.options.logFile) {
       this.currentTestLogFile = null;
@@ -254,7 +284,7 @@ export class TsTestLogger {
   }
   
   // TAP output forwarding (for TAP protocol messages)
-  tapOutput(message: string, isError: boolean = false) {
+  tapOutput(message: string, _isError: boolean = false) {
     if (this.options.json) return;
     
     // Never show raw TAP protocol messages in console
@@ -424,4 +454,48 @@ export class TsTestLogger {
       }
     }
   }
+  
+  // Create a diff between two log contents
+  private createDiff(previousContent: string, currentContent: string, filename: string): string {
+    const previousLines = previousContent.split('\n');
+    const currentLines = currentContent.split('\n');
+    
+    let diff = `DIFF REPORT: ${filename}\n`;
+    diff += `Generated: ${new Date().toISOString()}\n`;
+    diff += '='.repeat(80) + '\n\n';
+    
+    // Simple line-by-line comparison
+    const maxLines = Math.max(previousLines.length, currentLines.length);
+    let hasChanges = false;
+    
+    for (let i = 0; i < maxLines; i++) {
+      const prevLine = previousLines[i] || '';
+      const currLine = currentLines[i] || '';
+      
+      if (prevLine !== currLine) {
+        hasChanges = true;
+        if (i < previousLines.length && i >= currentLines.length) {
+          // Line was removed
+          diff += `- [Line ${i + 1}] ${prevLine}\n`;
+        } else if (i >= previousLines.length && i < currentLines.length) {
+          // Line was added
+          diff += `+ [Line ${i + 1}] ${currLine}\n`;
+        } else {
+          // Line was modified
+          diff += `- [Line ${i + 1}] ${prevLine}\n`;
+          diff += `+ [Line ${i + 1}] ${currLine}\n`;
+        }
+      }
+    }
+    
+    if (!hasChanges) {
+      diff += 'No changes detected.\n';
+    }
+    
+    diff += '\n' + '='.repeat(80) + '\n';
+    diff += `Previous version had ${previousLines.length} lines\n`;
+    diff += `Current version has ${currentLines.length} lines\n`;
+    
+    return diff;
+  }
 }