Stylish Formatter: output all file names (palantir#1557)

Currently the stylish formatter *only* prints the first fileName, and
then a list of lint errors from all files without specifying to which
file they belong.
After this fix, each time a new file is reached, a new line will be
added, and then the name of the file, so each group of lint failures
will be group with their fileName.

src/formatters/stylishFormatter.ts

@@ -26,15 +26,22 @@ export class Formatter extends AbstractFormatter {
             return "\n";
         }
 
-        const fileName        = failures[0].getFileName();
-        const positionMaxSize = this.getPositionMaxSize(failures);
-        const ruleMaxSize     = this.getRuleMaxSize(failures);
+        const outputLines: string[] = [];
+        const positionMaxSize       = this.getPositionMaxSize(failures);
+        const ruleMaxSize           = this.getRuleMaxSize(failures);
 
-        const outputLines = [
-            fileName,
-        ];
+        let currentFile: string;
 
         for (const failure of failures) {
+            const fileName = failure.getFileName();
+
+            // Output the name of each file once
+            if (currentFile !== fileName) {
+                outputLines.push("");
+                outputLines.push(fileName);
+                currentFile = fileName;
+            }
+
             const failureString = failure.getFailure();
 
             // Rule
@@ -55,6 +62,11 @@ export class Formatter extends AbstractFormatter {
             outputLines.push(output);
         }
 
+        // Removes initial blank line
+        if (outputLines[0] === "") {
+            outputLines.shift();
+        }
+
         return outputLines.join("\n") + "\n\n";
     }