Patch handle-callback-err

* Improve usage of checking first character (the use of an `indexOf` when it should be a quick single character check always irks me)
* Only check the first parameter (consistent with ESLint behaviour)
* Update the failure string to match ESLint
* Fix the position usage to avoid highlighting unrelated whitespace

src/rules/handleCallbackErrRule.ts

@@ -2,7 +2,7 @@ import * as ts from 'typescript';
 import * as Lint from 'tslint/lib/lint';
 
 export class Rule extends Lint.Rules.AbstractRule {
-  public static FAILURE_STRING = 'error parameter not handled';
+  public static FAILURE_STRING = 'Expected error to be handled';
 
   public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
     const languageService = Lint.createLanguageService(sourceFile.fileName, sourceFile.getFullText());
@@ -19,28 +19,28 @@ class ErrCallbackHandlerWalker extends Lint.RuleWalker {
     this.languageService = languageService;
     const customExpression = options.ruleArguments[0] || 'err';
 
-    if (customExpression.indexOf('^') === 0) {
+    if (customExpression.charAt(0) === '^') {
       this.errorRegex = new RegExp(customExpression);
     } else {
       this.errorRegex = new RegExp(`^${customExpression}$`);
     }
   }
 
   public visitFunctionDeclaration(node: ts.FunctionDeclaration) {
-    node.parameters
-      .filter(parameter => this.errorRegex.test(parameter.name.getText()))
-      .forEach((parameter) => {
-        this.validateReferencesForVariable(parameter.name.getText(), parameter.pos);
-      });
+    const parameter = node.parameters[0];
+
+    if (parameter && this.errorRegex.test(parameter.name.getText())) {
+      this.validateReferencesForVariable(parameter);
+    }
 
     super.visitFunctionDeclaration(node);
   }
 
-  private validateReferencesForVariable(name: string, position: number) {
+  private validateReferencesForVariable(node: ts.ParameterDeclaration) {
     const fileName = this.getSourceFile().fileName;
-    const highlights = this.languageService.getDocumentHighlights(fileName, position, [fileName]);
+    const highlights = this.languageService.getDocumentHighlights(fileName, node.pos, [fileName]);
     if (!highlights || highlights[0].highlightSpans.length <= 1) {
-      this.addFailure(this.createFailure(position, name.length, `${Rule.FAILURE_STRING}'${name}'`));
+      this.addFailure(this.createFailure(node.name.getStart(), node.name.getWidth(), Rule.FAILURE_STRING));
     }
   }
 }

src/test/rules/handleCallbackErrRuleTests.ts

@@ -11,13 +11,19 @@ const scripts = {
             console.log(err.stack);
         }
         doSomething();
-    }`,
+      }`,
       `function loadData (Err, data) {
         if (Err) {
             console.log(Err.stack);
         }
         doSomething();
-    }`
+      }`,
+      `function test (cb) {
+        doSomething(function (err) {
+          cb(err)
+        })
+      }`,
+      `function handle (arg, err) {}`
     ],
     invalid: [
       `function(err, stream) { stream.on('done', function(){exit(0)} }`,