{"action":"created","comment":{"url":"https://api.github.com/repos/Microsoft/TypeScript/pulls/comments/26272622","id":26272622,"diff_hunk":"@@ -439,7 +439,33 @@ module ts {\n                     var declaration = forEach(result.declarations, d => isBlockOrCatchScoped(d) ? d : undefined);\r\n \r\n                     Debug.assert(declaration !== undefined, \"Block-scoped variable declaration is undefined\");\r\n-                    if (!isDefinedBefore(declaration, errorLocation)) {\r\n+                    \r\n+                    // first check if usage is lexically located after the declaration\r\n+                    var isUsedBeforeDeclaration = !isDefinedBefore(declaration, errorLocation);\r\n+                    if (!isUsedBeforeDeclaration) {\r\n+                        // lexical check succedded however code still can be illegal.\r\n+                        // - block scoped variables cannot be used in its initializers\r\n+                        //   let x = x; // illegal but usage is lexically after definition\r\n+                        // - in ForIn/ForOf statements variable cannot be contained in expression part\r\n+                        //   for (let x in x)\r\n+                        //   for (let x of x)\r\n+\r\n+                        // climb up to the variable declaration skipping binding patterns\r\n+                        var variableDeclaration = <VariableDeclaration>getAncestor(declaration, SyntaxKind.VariableDeclaration);\r\n+                        var container = getEnclosingBlockScopeContainer(variableDeclaration);\r\n+\r\n+                        if (variableDeclaration.parent.parent.kind === SyntaxKind.VariableStatement ||\r\n+                            variableDeclaration.parent.parent.kind === SyntaxKind.ForStatement) {\r","path":"src/compiler/checker.ts","position":21,"original_position":21,"commit_id":"751b1aee16135d74d9e33eb24c62a505a8de314d","original_commit_id":"751b1aee16135d74d9e33eb24c62a505a8de314d","user":{"login":"JsonFreeman","id":8052525,"avatar_url":"https://avatars.githubusercontent.com/u/8052525?v=3","gravatar_id":"","url":"https://api.github.com/users/JsonFreeman","html_url":"https://github.com/JsonFreeman","followers_url":"https://api.github.com/users/JsonFreeman/followers","following_url":"https://api.github.com/users/JsonFreeman/following{/other_user}","gists_url":"https://api.github.com/users/JsonFreeman/gists{/gist_id}","starred_url":"https://api.github.com/users/JsonFreeman/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/JsonFreeman/subscriptions","organizations_url":"https://api.github.com/users/JsonFreeman/orgs","repos_url":"https://api.github.com/users/JsonFreeman/repos","events_url":"https://api.github.com/users/JsonFreeman/events{/privacy}","received_events_url":"https://api.github.com/users/JsonFreeman/received_events","type":"User","site_admin":false},"body":"Also, I noticed parameters are not handled. Is it okay for parameters to reference themselves in their default initializers?","created_at":"2015-03-12T01:40:54Z","updated_at":"2015-03-12T01:40:54Z","html_url":"https://github.com/Microsoft/TypeScript/pull/2309#discussion_r26272622","pull_request_url":"https://api.github.com/repos/Microsoft/TypeScript/pulls/2309","_links":{"self":{"href":"https://api.github.com/repos/Microsoft/TypeScript/pulls/comments/26272622"},"html":{"href":"https://github.com/Microsoft/TypeScript/pull/2309#discussion_r26272622"},"pull_request":{"href":"https://api.github.com/repos/Microsoft/TypeScript/pulls/2309"}}},"pull_request":{"url":"https://api.github.com/repos/Microsoft/TypeScript/pulls/2309","id":30998761,"html_url":"https://github.com/Microsoft/TypeScript/pull/2309","diff_url":"https://github.com/Microsoft/TypeScript/pull/2309.diff","patch_url":"https://github.com/Microsoft/TypeScript/pull/2309.patch","issue_url":"https://api.github.com/repos/Microsoft/TypeScript/issues/2309","number":2309,"state":"open","locked":false,"title":"disallow recursive references for 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