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‎docs/codeql/codeql-language-guides/basic-query-for-swift-code.rst

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.. _basic-query-for-swift-code:
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Basic query for Swift code
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=========================
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Learn to write and run a simple CodeQL query using Visual Studio Code with the CodeQL extension.
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.. include:: ../reusables/vs-code-basic-instructions/setup-to-run-queries.rst
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About the query
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---------------
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The query we're going to run performs a basic search of the code for ``if`` expressions that are redundant, in the sense that they have an empty ``then`` branch. For example, code such as:
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.. code-block:: swift
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if error {
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// we should handle the error
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}
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.. include:: ../reusables/vs-code-basic-instructions/find-database.rst
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Running a quick query
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---------------------
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.. include:: ../reusables/vs-code-basic-instructions/run-quick-query-1.rst
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#. In the quick query tab, delete the content and paste in the following query.
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.. code-block:: ql
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import swift
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from IfStmt ifStmt
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where ifStmt.getThen().(BraceStmt).getNumberOfElements() = 0
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select ifStmt, "This 'if' statement is redundant."
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.. include:: ../reusables/vs-code-basic-instructions/run-quick-query-2.rst
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.. image:: ../images/codeql-for-visual-studio-code/basic-swift-query-results-1.png
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:align: center
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If any matching code is found, click a link in the ``ifStmt`` column to open the file and highlight the matching ``if`` statement.
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.. image:: ../images/codeql-for-visual-studio-code/basic-swift-query-results-2.png
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:align: center
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.. include:: ../reusables/vs-code-basic-instructions/note-store-quick-query.rst
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About the query structure
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~~~~~~~~~~~~~~~~~~~~~~~~~
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After the initial ``import`` statement, this simple query comprises three parts that serve similar purposes to the FROM, WHERE, and SELECT parts of an SQL query.
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+------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
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| Query part | Purpose | Details |
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+==================================================================+===================================================================================================================+=================================================================================================+
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| ``import swift`` | Imports the standard CodeQL AST libraries for Swift. | Every query begins with one or more ``import`` statements. |
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+------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
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| ``from IfStmt ifStmt`` | Defines the variables for the query. | We use: an ``IfStmt`` variable for ``if`` statements. |
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| | Declarations are of the form: | |
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| | ``<type> <variable name>`` | |
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+------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
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| ``where ifStmt.getThen().(BraceStmt).getNumberOfElements() = 0`` | Defines a condition on the variables. | ``ifStmt.getThen()``: gets the ``then`` branch of the ``if`` expression. |
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| | | ``.(BraceStmt)``: requires that the ``then`` branch is a brace statement (``{ }``). |
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| | | ``.getNumberOfElements() = 0``: requires that the brace statement contains no child statements. |
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+------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
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| ``select ifStmt, "This 'if' statement is redundant."`` | Defines what to report for each match. | Reports the resulting ``if`` statement with a string that explains the problem. |
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| | | |
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| | ``select`` statements for queries that are used to find instances of poor coding practice are always in the form: | |
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| | ``select <program element>, "<alert message>"`` | |
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+------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
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Extend the query
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----------------
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Query writing is an inherently iterative process. You write a simple query and then, when you run it, you discover examples that you had not previously considered, or opportunities for improvement.
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Remove false positive results
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Browsing the results of our basic query shows that it could be improved. Among the results you are likely to find examples of ``if`` statements with an ``else`` branch, where an empty ``then`` branch does serve a purpose. For example:
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.. code-block:: swift
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if (option == "-verbose") {
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// nothing to do - handled earlier
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} else {
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handleError("unrecognized option")
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}
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In this case, identifying the ``if`` statement with the empty ``then`` branch as redundant is a false positive. One solution to this is to modify the query to select ``if`` statements where both the ``then`` and ``else`` branches are missing.
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To exclude ``if`` statements that have an ``else`` branch:
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#. Add the following to the where clause:
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.. code-block:: ql
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and not exists(ifStmt.getElse())
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The ``where`` clause is now:
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.. code-block:: ql
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where
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ifStmt.getThen().(BraceStmt).getNumberOfElements() = 0 and
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not exists(ifStmt.getElse())
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#. Re-run the query.
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There are now fewer results because ``if`` expressions with an ``else`` branch are no longer included.
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Further reading
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---------------
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.. include:: ../reusables/swift-further-reading.rst
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.. include:: ../reusables/codeql-ref-tools-further-reading.rst
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.. Article-specific substitutions for the reusables used in docs/codeql/reusables/vs-code-basic-instructions
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.. |language-text| replace:: Swift
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.. |language-code| replace:: ``swift``
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.. |example-url| replace:: https://github.com/alamofire/alamofire
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.. |image-quick-query| image:: ../images/codeql-for-visual-studio-code/quick-query-tab-swift.png
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.. |result-col-1| replace:: The first column corresponds to the expression ``ifStmt`` and is linked to the location in the source code of the project where ``ifStmt`` occurs.

‎docs/codeql/codeql-language-guides/codeql-for-swift.rst

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.. _codeql-for-swift:
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CodeQL for Swift
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===============
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Experiment and learn how to write effective and efficient queries for CodeQL databases generated from Swift codebases.
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.. toctree::
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:hidden:
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basic-query-for-swift-code
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- :doc:`Basic query for Swift code <basic-query-for-swift-code>`: Learn to write and run a simple CodeQL query.

‎docs/codeql/codeql-language-guides/index.rst

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codeql-for-javascript
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codeql-for-python
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codeql-for-ruby
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codeql-for-swift

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