diff --git a/docs/codeql/codeql-language-guides/basic-query-for-rust-code.rst b/docs/codeql/codeql-language-guides/basic-query-for-rust-code.rst new file mode 100644 index 00000000000..9e146513a20 --- /dev/null +++ b/docs/codeql/codeql-language-guides/basic-query-for-rust-code.rst @@ -0,0 +1,130 @@ +.. _basic-query-for-swift-code: + +Basic query for Swift code +========================== + +Learn to write and run a simple CodeQL query using Visual Studio Code with the CodeQL extension. + +.. include:: ../reusables/vs-code-basic-instructions/setup-to-run-queries.rst + +About the query +--------------- + +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: + +.. code-block:: swift + + if error { + // we should handle the error + } + +.. include:: ../reusables/vs-code-basic-instructions/find-database.rst + +Running a quick query +--------------------- + +.. include:: ../reusables/vs-code-basic-instructions/run-quick-query-1.rst + +#. In the quick query tab, delete the content and paste in the following query. + + .. code-block:: ql + + import swift + + from IfStmt ifStmt + where ifStmt.getThen().(BraceStmt).getNumberOfElements() = 0 + select ifStmt, "This 'if' statement is redundant." + +.. include:: ../reusables/vs-code-basic-instructions/run-quick-query-2.rst + +.. image:: ../images/codeql-for-visual-studio-code/basic-swift-query-results-1.png + :align: center + +If any matching code is found, click a link in the ``ifStmt`` column to open the file and highlight the matching ``if`` statement. + +.. image:: ../images/codeql-for-visual-studio-code/basic-swift-query-results-2.png + :align: center + +.. include:: ../reusables/vs-code-basic-instructions/note-store-quick-query.rst + +About the query structure +~~~~~~~~~~~~~~~~~~~~~~~~~ + +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. + ++------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+ +| Query part | Purpose | Details | ++==================================================================+===================================================================================================================+=================================================================================================+ +| ``import swift`` | Imports the standard CodeQL AST libraries for Swift. | Every query begins with one or more ``import`` statements. | ++------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+ +| ``from IfStmt ifStmt`` | Defines the variables for the query. | We use: an ``IfStmt`` variable for ``if`` statements. | +| | Declarations are of the form: | | +| | `` `` | | ++------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+ +| ``where ifStmt.getThen().(BraceStmt).getNumberOfElements() = 0`` | Defines a condition on the variables. | ``ifStmt.getThen()``: gets the ``then`` branch of the ``if`` expression. | +| | | ``.(BraceStmt)``: requires that the ``then`` branch is a brace statement (``{ }``). | +| | | ``.getNumberOfElements() = 0``: requires that the brace statement contains no child statements. | ++------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+ +| ``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. | +| | | | +| | ``select`` statements for queries that are used to find instances of poor coding practice are always in the form: | | +| | ``select , ""`` | | ++------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+ + +Extend the query +---------------- + +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. + +Remove false positive results +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +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: + +.. code-block:: swift + + if (option == "-verbose") { + // nothing to do - handled earlier + } else { + handleError("unrecognized option") + } + +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. + +To exclude ``if`` statements that have an ``else`` branch: + +#. Add the following to the where clause: + + .. code-block:: ql + + and not exists(ifStmt.getElse()) + + The ``where`` clause is now: + + .. code-block:: ql + + where + ifStmt.getThen().(BraceStmt).getNumberOfElements() = 0 and + not exists(ifStmt.getElse()) + +#. Re-run the query. + + There are now fewer results because ``if`` expressions with an ``else`` branch are no longer included. + +Further reading +--------------- + +.. include:: ../reusables/swift-further-reading.rst +.. include:: ../reusables/codeql-ref-tools-further-reading.rst + +.. Article-specific substitutions for the reusables used in docs/codeql/reusables/vs-code-basic-instructions + +.. |language-text| replace:: Swift + +.. |language-code| replace:: ``swift`` + +.. |example-url| replace:: https://github.com/alamofire/alamofire + +.. |image-quick-query| image:: ../images/codeql-for-visual-studio-code/quick-query-tab-swift.png + +.. |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. diff --git a/docs/codeql/codeql-language-guides/codeql-for-rust.rst b/docs/codeql/codeql-language-guides/codeql-for-rust.rst index 24292909467..4d68f080b87 100644 --- a/docs/codeql/codeql-language-guides/codeql-for-rust.rst +++ b/docs/codeql/codeql-language-guides/codeql-for-rust.rst @@ -12,5 +12,8 @@ Experiment and learn how to write effective and efficient queries for CodeQL dat codeql-library-for-rust analyzing-data-flow-in-rust +- :doc:`Basic query for Rust code `: Learn to write and run a simple CodeQL query. + - :doc:`CodeQL library for Rust `: When analyzing Rust code, you can make use of the large collection of classes in the CodeQL library for Rust. + - :doc:`Analyzing data flow in Rust `: You can use CodeQL to track the flow of data through a Rust program to places where the data is used.