Add errors for declarations which conflict with catch parameters.

test/mjsunit/es6/catch-parameter-redeclaration.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function checkIsRedeclarationError(code) {
+  try {
+    eval(`
+checkIsRedeclarationError : {
+  break checkIsRedeclarationError;
+${code}
+}
+`);
+    assertUnreachable();
+  } catch(e) {
+    assertInstanceof(e, SyntaxError );
+    assertTrue( e.toString().indexOf("has already been declared") >= 0 );
+  }
+}
+
+function checkIsNotRedeclarationError(code) {
+  assertDoesNotThrow(()=>eval(`
+checkIsNotRedeclarationError_label : {
+  break checkIsNotRedeclarationError_label;
+${code}
+}
+`));
+}
+
+
+let lexical_e = [
+  'let e',
+  'let f, g, e',
+  'let [f] = [], [] = [], e = e, h',
+  'let {e} = 0',
+  'let {f, e} = 0',
+  'let {f, g} = 0, {e} = 0',
+  'let {f = 0, e = 1} = 0',
+  'let [e] = 0',
+  'let [f, e] = 0',
+  'let {f:e} = 0',
+  'let [[[], e]] = 0',
+  'const e = 0',
+  'const f = 0, g = 0, e = 0',
+  'const {e} = 0',
+  'const [e] = 0',
+  'const {f:e} = 0',
+  'const [[[], e]] = 0',
+  'function e(){}',
+  'function* e(){}',
+];
+
+let not_lexical_e = [
+  'var e',
+  'var f, e',
+  'var {e} = 0',
+  'let {} = 0',
+  'let {e:f} = 0',
+  '{ function e(){} }'
+];
+
+// Check that lexical declarations cannot override a simple catch parameter
+for (let declaration of lexical_e) {
+  checkIsRedeclarationError(`
+try {
+  throw 0;
+} catch(e) {
+  ${declaration}
+}
+`);
+}
+
+// Check that lexical declarations cannot override a complex catch parameter
+for (let declaration of lexical_e) {
+  checkIsRedeclarationError(`
+try {
+  throw 0;
+} catch({e}) {
+  ${declaration}
+}
+`);
+}
+
+// Check that non-lexical declarations can override a simple catch parameter
+for (let declaration of not_lexical_e) {
+  checkIsNotRedeclarationError(`
+try {
+  throw 0;
+} catch(e) {
+  ${declaration}
+}
+`);
+}
+
+// Check that the above error does not occur if a declaration scope is between
+// the catch and the loop.
+for (let declaration of lexical_e) {
+  checkIsNotRedeclarationError(`
+try {
+  throw 0;
+} catch(e) {
+  (()=>{${declaration}})();
+}
+`);
+
+  checkIsNotRedeclarationError(`
+try {
+  throw 0;
+} catch(e) {
+  (function(){${declaration}})();
+}
+`);
+}