[editorial][CI] Ensure markdownlint has proper exit status (open-telemetry#210)

Co-authored-by: Josh Suereth <joshuasuereth@google.com>

Author: chalin

gulpfile.js

@@ -4,8 +4,8 @@ const markdownlint = require("markdownlint");
 const yaml = require("js-yaml");
 const fs = require("fs");
 
-let fileCount = 0,
-  issueCount = 0;
+let numFilesProcessed = 0,
+  numFilesWithIssues = 0;
 
 function markdownLintFile(file, encoding, callback) {
   const config = yaml.load(fs.readFileSync("./.markdownlint.yaml", "utf8"));
@@ -33,9 +33,11 @@ function markdownLintFile(file, encoding, callback) {
       .join("\n");
     if (resultString) {
       console.log(resultString);
-      issueCount++;
+      numFilesWithIssues++;
+      // Don't report an error yet so that other files can be checked:
+      // callback(new Error('...'));
     }
-    fileCount++;
+    numFilesProcessed++;
     callback(null, file);
   });
 }
@@ -47,11 +49,13 @@ function lintMarkdown() {
     .src(markdownFiles)
     .pipe(through2.obj(markdownLintFile))
     .on("end", () => {
-      console.log(
-        `Processed ${fileCount} file${
-          fileCount == 1 ? "" : "s"
-        }, ${issueCount} had issues.`,
-      );
+      const fileOrFiles = "file" + (numFilesProcessed == 1 ? "" : "s");
+      const msg = `Processed ${numFilesProcessed} ${fileOrFiles}, ${numFilesWithIssues} had issues.`;
+      if (numFilesWithIssues > 0) {
+        throw new Error(msg);
+      } else {
+        console.log(msg);
+      }
     });
 }