tools: enable no-redeclare rule for linter

PR-URL: #5047
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

.eslintrc

@@ -48,6 +48,8 @@ rules:
   # list: https://github.com/eslint/eslint/tree/master/docs/rules#best-practices
   ## require falls through comment on switch-case
   no-fallthrough: 2
+  ## disallow declaring the same variable more than once
+  no-redeclare: 2
 
   # Stylistic Issues
   # list: https://github.com/eslint/eslint/tree/master/docs/rules#stylistic-issues

lib/dgram.js

@@ -332,7 +332,7 @@ Socket.prototype.send = function(buffer,
                                   !!callback);
       if (err && callback) {
         // don't emit as error, dgram_legacy.js compatibility
-        var ex = exceptionWithHostPort(err, 'send', address, port);
+        const ex = exceptionWithHostPort(err, 'send', address, port);
         process.nextTick(callback, ex);
       }
     }

test/parallel/test-crypto-dh.js

@@ -152,10 +152,10 @@ assert.equal(bad_dh.verifyError, constants.DH_NOT_SUITABLE_GENERATOR);
 // Test ECDH
 var ecdh1 = crypto.createECDH('prime256v1');
 var ecdh2 = crypto.createECDH('prime256v1');
-var key1 = ecdh1.generateKeys();
-var key2 = ecdh2.generateKeys('hex');
-var secret1 = ecdh1.computeSecret(key2, 'hex', 'base64');
-var secret2 = ecdh2.computeSecret(key1, 'binary', 'buffer');
+key1 = ecdh1.generateKeys();
+key2 = ecdh2.generateKeys('hex');
+secret1 = ecdh1.computeSecret(key2, 'hex', 'base64');
+secret2 = ecdh2.computeSecret(key1, 'binary', 'buffer');
 
 assert.equal(secret1, secret2.toString('base64'));
 
@@ -168,7 +168,7 @@ crypto.createHash('sha256');
 assert.equal(ecdh1.getPublicKey('buffer', 'uncompressed')[0], 4);
 var firstByte = ecdh1.getPublicKey('buffer', 'compressed')[0];
 assert(firstByte === 2 || firstByte === 3);
-var firstByte = ecdh1.getPublicKey('buffer', 'hybrid')[0];
+firstByte = ecdh1.getPublicKey('buffer', 'hybrid')[0];
 assert(firstByte === 6 || firstByte === 7);
 
 // ECDH should check that point is on curve

test/parallel/test-fs-utimes.js

@@ -18,7 +18,7 @@ function stat_resource(resource) {
 }
 
 function check_mtime(resource, mtime) {
-  var mtime = fs._toUnixTimestamp(mtime);
+  mtime = fs._toUnixTimestamp(mtime);
   var stats = stat_resource(resource);
   var real_mtime = fs._toUnixTimestamp(stats.mtime);
   // check up to single-second precision