fix(@angular/cli): ensure lint generates well-formed machine output

For machine readable output formats, ng lint was concatenating multiple documents into a single file. This resulted in invalid JSON, XML, etc. The lint results are now aggregated and one full output is generated.

Fix #5259
Close #5224

packages/@angular/cli/tasks/lint.ts

@@ -33,11 +33,8 @@ export default Task.extend({
     const Linter = tslint.Linter;
     const Configuration = tslint.Configuration;
 
-    let errors = 0;
-    let results = '';
-
-    lintConfigs
-      .forEach((config) => {
+    const result = lintConfigs
+      .map((config) => {
         const program: ts.Program = Linter.createProgram(config.project);
         const files = getFilesToLint(program, config, Linter);
 
@@ -56,19 +53,37 @@ export default Task.extend({
           linter.lint(file, fileContents, configLoad.results);
         });
 
-        const result = linter.getResult();
-        errors += result.failureCount;
-        results = results.concat(result.output.trim().concat('\n'));
+        return linter.getResult();
+      })
+      .reduce((total, current) => {
+        const failures = current.failures
+          .filter((cf: any) => !total.failures.some((ef: any) => ef.equals(cf)));
+        total.failures = total.failures.concat(...failures);
+
+        if (current.fixes) {
+          total.fixes = (total.fixes || []).concat(...current.fixes);
+        }
+        return total;
+      }, {
+        failures: [],
+        fixes: undefined
       });
 
+    const Formatter = tslint.findFormatter(commandOptions.format);
+    const formatter = new Formatter();
+
+    const output = formatter.format(result.failures, result.fixes);
+    if (output) {
+      ui.writeLine(output);
+    }
+
     // print formatter output directly for non human-readable formats
     if (['prose', 'verbose', 'stylish'].indexOf(commandOptions.format) == -1) {
-      ui.writeLine(results.trim());
-      return (errors == 0 || commandOptions.force) ? Promise.resolve(0) : Promise.resolve(2);
+      return (result.failures.length == 0 || commandOptions.force)
+            ? Promise.resolve(0) : Promise.resolve(2);
     }
 
-    if (errors > 0) {
-      ui.writeLine(results.trim());
+    if (result.failures.length > 0) {
       ui.writeLine(chalk.red('Lint errors found in the listed files.'));
       return commandOptions.force ? Promise.resolve(0) : Promise.resolve(2);
     }