Add auto-fix for no-var-keyword (#1547)

Note, we just replace with `let` which can cause errors if the identifier is referenced before the declaration or outside the scope. TypeScript will catch these at type-check time.

src/rules/noVarKeywordRule.ts

@@ -44,7 +44,8 @@ class NoVarKeywordWalker extends Lint.RuleWalker {
     public visitVariableStatement(node: ts.VariableStatement) {
         if (!Lint.hasModifier(node.modifiers, ts.SyntaxKind.DeclareKeyword)
                 && !Lint.isBlockScopedVariable(node)) {
-            this.addFailure(this.createFailure(node.declarationList.getStart(), "var".length, Rule.FAILURE_STRING));
+            this.addFailure(this.createFailure(node.declarationList.getStart(), "var".length, Rule.FAILURE_STRING,
+                 this.fix(node.declarationList)));
         }
 
         super.visitVariableStatement(node);
@@ -68,7 +69,12 @@ class NoVarKeywordWalker extends Lint.RuleWalker {
     private handleInitializerNode(node: ts.VariableDeclarationList | ts.Expression) {
         if (node && node.kind === ts.SyntaxKind.VariableDeclarationList &&
                 !(Lint.isNodeFlagSet(node, ts.NodeFlags.Let) || Lint.isNodeFlagSet(node, ts.NodeFlags.Const))) {
-            this.addFailure(this.createFailure(node.getStart(), "var".length, Rule.FAILURE_STRING));
+            this.addFailure(this.createFailure(node.getStart(), "var".length, Rule.FAILURE_STRING, this.fix(node)));
         }
     }
+
+    private fix = (node: ts.Node) => new Lint.Fix(Rule.metadata.ruleName, [
+        this.deleteText(node.getStart(), "var".length),
+        this.appendText(node.getStart(), "let"),
+    ]);
 }

test/rules/no-var-keyword/test.ts.fix

@@ -0,0 +1,44 @@
+let foo;
+
+function tmp(t: any) {
+    let x = 3;
+}
+
+let i,
+    j;
+
+let [a, b] = [1, 2];
+
+for (let n; false;);
+for (let n1 in foo);
+for (let n2 of foo);
+
+export let exportVar0 = 0;
+export   let  exportVar1 = 1;
+export   let  exportVar2 = 2,
+         exportVar21 = 21;
+export /* var tst */ let   exportVar3 = 3;
+
+module quz {
+    export let i;
+}
+
+declare var tmp2: any;
+
+let bar;
+const qux;
+
+let k,
+    l;
+
+let [x, y] = [1, 2];
+
+for (n; false;);
+for (let n; false;);
+for (let name in foo);
+for (let name of foo);
+for (const name in foo);
+for (const name of foo);
+
+export let exportLet = 1;
+export const exportConst = 1;