Fix scope of catch block (#5980)

* Fix scope of catch block

* Throw error on Duplicate variable declaration

* Update test

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/issue-5979/actual.js

@@ -0,0 +1 @@
+try {} catch (a) { let a }

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/issue-5979/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Duplicate declaration \"a\""
+}

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/issue-T7525/actual.js

@@ -8,9 +8,3 @@ for (let a in [1, 2, 3]) {
   let a = 3;
   console.log(a);
 }
-
-try {
-    throw new Error();
-} catch(a) {
-    let a = 4;
-}

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/issue-T7525/expected.js

@@ -8,9 +8,3 @@ for (var _a2 in [1, 2, 3]) {
   var _a3 = 3;
   console.log(_a3);
 }
-
-try {
-  throw new Error();
-} catch (_a4) {
-  var _a5 = 4;
-}

packages/babel-types/src/definitions/core.js

@@ -154,7 +154,7 @@ defineType("CatchClause", {
       validate: assertNodeType("BlockStatement"),
     },
   },
-  aliases: ["Scopable"],
+  aliases: ["Scopable", "BlockParent"],
 });
 
 defineType("ConditionalExpression", {

packages/babel-types/src/validators.js

@@ -231,6 +231,10 @@ export function isScope(node: Object, parent: Object): boolean {
     return false;
   }
 
+  if (t.isBlockStatement(node) && t.isCatchClause(parent, { body: node })) {
+    return false;
+  }
+
   return t.isScopable(node);
 }