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 <h1>Open Clang Projects</h1>

 <p>Here are a few tasks that are available for anyone to work on, depending
 on what your interests are. This list is provided to generate ideas, it is not
 intended to be comprehensive. Please ask on
 <a href="https://discourse.llvm.org/c/clang">Discourse</a> for more specifics
 or to verify that one of these isn't already completed.</p>

 <ul>
 <li><b>Refresh and improve Clang's documentation</b>: Clang is inconsistent
 with documenting implementation-defined behaviors. We have significant
 documentation in the <a href="https://clang.llvm.org/docs/LanguageExtensions.html">
 Language Extensions</a> page, but the information is incomplete and the page is
 difficult to navigate. We would appreciate help with:
 <ul>
   <li>improving the way this information is presented to users,</li>
   <li><a href="https://llvm.org/docs/TableGen/">table generating</a>
       documentation where possible, such as for implementation limits or other
       target-specific information,</li>
   <li>adding documentation for currently
      <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/AttrDocs.td">
      undocumented attributes</a>,</li>
   <li>documenting <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/DiagnosticDocs.td">
       diagnostic group flags</a> (adding code examples of what is diagnosed, or
       other relevant information), or</li>
   <li>documenting <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Driver/Options.td">
       command line options</a>, or</li>
   <li>help with completing other missing documentation.</li>
 </ul>
 These projects are independent of each other.</li>

 <li><b>Complete the investigation into Clang's C conformance</b>: Clang's
 <a href="c_status.html">C status page</a> contain a number of entries marked as
 <code>Unknown</code>. Completing the investigation involves adding
 <a href="https://github.com/llvm/llvm-project/tree/main/clang/test/C">test
 coverage</a> for the various standards papers and updating the documentation
 accordingly.
 </li>

 <li><b>Improve Clang's C and C++ standard conformance test coverage</b>:
 Clang's test suite is structured such that most tests are written to provide
 coverage for what part of the compiler the feature's implementation exists in;
 we have parsing tests in <code>clang/test/Parser</code>, and semantic analysis
 tests in <code>clang/test/Sema*</code>, etc. We also have tests written to
 provide coverage for the standard requirements (<code>clang/test/CXX</code> and
 <code>clang/test/C</code>). The standards coverage is not structured in a way
 that makes it easy to maintain as the standards change over time. No commercial
 conformance test suite has a license model suitable for open source projects,
 so we would appreciate help in improving the existing coverage we have both in
 terms of layout of the tests as well as in coverage of the various standard
 modes.</li>

 <li><b>Complete the investigation into Clang's C and C++ Defect Report
 conformance</b>: Separate from (but related to) general conformance testing is
 determining which <a href="c_dr_status.html">C defect reports</a> and
 <a href="cxx_dr_status.html">C++ defect reports</a> Clang implements. These
 lists currently have a number of entries marked as <code>Unknown</code>.
 Completing the investigation involves adding test coverage for
 <a href="https://github.com/llvm/llvm-project/tree/main/clang/test/C/drs">C</a>
 and
 <a href="https://github.com/llvm/llvm-project/tree/main/clang/test/CXX/drs">C++</a>
 defect reports and updating the documentation accordingly.</li>

 <li><b>Bug triage</b>: Clang's <a href="https://github.com/llvm/llvm-project/issues">
 issue tracker</a>currently has over 20,000 open issues, many of which are not
 appropriately tagged, are no longer reproducible, could use a reduced test case,
 or otherwise needs some manual interaction. We can always use help with
 <a href="https://llvm.org/docs/BugLifeCycle.html#triaging-bugs">bug triage and
 issue tracker maintenance</a>.
 </li>

 <li><b>Improve build times with Clang</b>: the time it takes Clang to process a
 translation unit is very important to our users; the lower the build time, the
 better the overall user experience. It would be good to improve Clang's
 performance as well as to find ways to proactively alert us when we've
 introduced a change that has significant negative impact on build times.</li>

 <li><b>Complete support for the experimental constant expression interpreter
 </b>: Clang's production constant expression interpreter computes a constant
 expression result by walking over AST nodes, performing calculations as it
 goes. This does not have good performance properties, and so we've begun work
 on an <a href="https://clang.llvm.org/docs/ConstantInterpreter.html">
 experimental constant expression interpreter</a> that works by converting the
 AST into bytecode that is interpreted. This effort has a long tail of work left
 to complete because it requires implementing byte code for every kind of
 expression and type that can be used in a constant expression for C++ and C.
 </li>

 <li><b>Improve clang-doc</b>: Clang's library-based design allows it to be used
 by a variety of tools that reason about source code.
 <a href="https://clang.llvm.org/extra/clang-doc.html">clang-doc</a> is one
 great application of this functionality, which generates code documentation
 from source code. The tool is in early stages of development and could use more
 dedicated effort to complete the implementation.</li>

 <li><b>Self-testing using clang</b>: There are several neat ways to
 improve the quality of clang by self-testing. Some examples:
 <ul>
   <li>Improve the reliability of AST printing and serialization by
   ensuring that the AST produced by clang on an input doesn't change
   when it is reparsed or unserialized.

   <li>Improve parser reliability and error generation by automatically
   or randomly changing the input checking that clang doesn't crash and
   that it doesn't generate excessive errors for small input
   changes. Manipulating the input at both the text and token levels is
   likely to produce interesting test cases.
 </ul>
 </li>

 <li><b>Continue work on C++20, C++23, C++2c, and C23 support</b>:
   There are still several C++20 features to complete, and work has begun on
   supporting the latest language standards. Please see the
   <a href="cxx_status.html">C++ status report page</a> to find out what is
   missing.</li>

 <li><b>StringRef'ize APIs</b>: A thankless but incredibly useful project is
 StringRef'izing (converting to use <tt>llvm::StringRef</tt> instead of <tt>const
 char *</tt> or <tt>std::string</tt>) various clang interfaces. This generally
 simplifies the code and makes it more efficient.</li>

 <li><b>Configuration Manager</b>: Clang/LLVM works on a large number of
 architectures and operating systems and can cross-compile to a similarly large
 number of configurations, but the pitfalls of choosing the command-line
 options, making sure the right sub-architecture is chosen and that the correct
 optional elements of your particular system can be a pain.

 <p>A tool that would investigate hosts and targets, and store the configuration
 in files that can later be used by Clang itself to avoid command-line options,
 especially the ones regarding which target options to use, would greatly alleviate
 this problem. A simple tool, with little or no dependency on LLVM itself, that
 will investigate a target architecture by probing hardware, software, libraries
 and compiling and executing code to identify all properties that would be relevant
 to command-line options (VFP, SSE, NEON, ARM vs. Thumb etc), triple settings etc.</p>

 <p>The first stage is to build a CFLAGS for Clang that would produce code on the
 current Host to the identified Target.</p>

 <p>The second stage would be to produce a configuration file (that can be used
 independently of the Host) so that Clang can read it and not need a gazillion
 of command-line options. Such file should be simple JSON / INI or anything that
 a text editor could change.</p></li>
 </ul>

 <p>If you hit a bug with Clang, it is very useful for us if you reduce the code
 that demonstrates the problem down to something small. There are many ways to
 do this; ask on <a href="https://discourse.llvm.org/c/clang">Discourse</a>,
 <a href="https://discord.com/channels/636084430946959380/636725486533345280">Discord</a>,
 or <a href="https://llvm.org/docs/GettingInvolved.html#irc"IRC</a> for advice.</p>

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	<META http-equiv="Content-Type" content="text/html; charset=utf-8">
	<title>Clang - Open Projects</title>
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	<link type="text/css" rel="stylesheet" href="content.css">
	</head>
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	<!--#include virtual="menu.html.incl"-->

	<div id="content">

	<h1>Open Clang Projects</h1>

	<p>Here are a few tasks that are available for anyone to work on, depending
	on what your interests are. This list is provided to generate ideas, it is not
	intended to be comprehensive. Please ask on
	<a href="https://discourse.llvm.org/c/clang">Discourse</a> for more specifics
	or to verify that one of these isn't already completed.</p>

	<ul>
	<li><b>Refresh and improve Clang's documentation</b>: Clang is inconsistent
	with documenting implementation-defined behaviors. We have significant
	documentation in the <a href="https://clang.llvm.org/docs/LanguageExtensions.html">
	Language Extensions</a> page, but the information is incomplete and the page is
	difficult to navigate. We would appreciate help with:
	<ul>
	<li>improving the way this information is presented to users,</li>
	<li><a href="https://llvm.org/docs/TableGen/">table generating</a>
	documentation where possible, such as for implementation limits or other
	target-specific information,</li>
	<li>adding documentation for currently
	<a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/AttrDocs.td">
	undocumented attributes</a>,</li>
	<li>documenting <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/DiagnosticDocs.td">
	diagnostic group flags</a> (adding code examples of what is diagnosed, or
	other relevant information), or</li>
	<li>documenting <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Driver/Options.td">
	command line options</a>, or</li>
	<li>help with completing other missing documentation.</li>
	</ul>
	These projects are independent of each other.</li>

	<li><b>Complete the investigation into Clang's C conformance</b>: Clang's
	<a href="c_status.html">C status page</a> contain a number of entries marked as
	<code>Unknown</code>. Completing the investigation involves adding
	<a href="https://github.com/llvm/llvm-project/tree/main/clang/test/C">test
	coverage</a> for the various standards papers and updating the documentation
	accordingly.
	</li>

	<li><b>Improve Clang's C and C++ standard conformance test coverage</b>:
	Clang's test suite is structured such that most tests are written to provide
	coverage for what part of the compiler the feature's implementation exists in;
	we have parsing tests in <code>clang/test/Parser</code>, and semantic analysis
	tests in <code>clang/test/Sema*</code>, etc. We also have tests written to
	provide coverage for the standard requirements (<code>clang/test/CXX</code> and
	<code>clang/test/C</code>). The standards coverage is not structured in a way
	that makes it easy to maintain as the standards change over time. No commercial
	conformance test suite has a license model suitable for open source projects,
	so we would appreciate help in improving the existing coverage we have both in
	terms of layout of the tests as well as in coverage of the various standard
	modes.</li>

	<li><b>Complete the investigation into Clang's C and C++ Defect Report
	conformance</b>: Separate from (but related to) general conformance testing is
	determining which <a href="c_dr_status.html">C defect reports</a> and
	<a href="cxx_dr_status.html">C++ defect reports</a> Clang implements. These
	lists currently have a number of entries marked as <code>Unknown</code>.
	Completing the investigation involves adding test coverage for
	<a href="https://github.com/llvm/llvm-project/tree/main/clang/test/C/drs">C</a>
	and
	<a href="https://github.com/llvm/llvm-project/tree/main/clang/test/CXX/drs">C++</a>
	defect reports and updating the documentation accordingly.</li>

	<li><b>Bug triage</b>: Clang's <a href="https://github.com/llvm/llvm-project/issues">
	issue tracker</a>currently has over 20,000 open issues, many of which are not
	appropriately tagged, are no longer reproducible, could use a reduced test case,
	or otherwise needs some manual interaction. We can always use help with
	<a href="https://llvm.org/docs/BugLifeCycle.html#triaging-bugs">bug triage and
	issue tracker maintenance</a>.
	</li>

	<li><b>Improve build times with Clang</b>: the time it takes Clang to process a
	translation unit is very important to our users; the lower the build time, the
	better the overall user experience. It would be good to improve Clang's
	performance as well as to find ways to proactively alert us when we've
	introduced a change that has significant negative impact on build times.</li>

	<li><b>Complete support for the experimental constant expression interpreter
	</b>: Clang's production constant expression interpreter computes a constant
	expression result by walking over AST nodes, performing calculations as it
	goes. This does not have good performance properties, and so we've begun work
	on an <a href="https://clang.llvm.org/docs/ConstantInterpreter.html">
	experimental constant expression interpreter</a> that works by converting the
	AST into bytecode that is interpreted. This effort has a long tail of work left
	to complete because it requires implementing byte code for every kind of
	expression and type that can be used in a constant expression for C++ and C.
	</li>

	<li><b>Improve clang-doc</b>: Clang's library-based design allows it to be used
	by a variety of tools that reason about source code.
	<a href="https://clang.llvm.org/extra/clang-doc.html">clang-doc</a> is one
	great application of this functionality, which generates code documentation
	from source code. The tool is in early stages of development and could use more
	dedicated effort to complete the implementation.</li>

	<li><b>Self-testing using clang</b>: There are several neat ways to
	improve the quality of clang by self-testing. Some examples:
	<ul>
	<li>Improve the reliability of AST printing and serialization by
	ensuring that the AST produced by clang on an input doesn't change
	when it is reparsed or unserialized.

	<li>Improve parser reliability and error generation by automatically
	or randomly changing the input checking that clang doesn't crash and
	that it doesn't generate excessive errors for small input
	changes. Manipulating the input at both the text and token levels is
	likely to produce interesting test cases.
	</ul>
	</li>

	<li><b>Continue work on C++20, C++23, C++2c, and C23 support</b>:
	There are still several C++20 features to complete, and work has begun on
	supporting the latest language standards. Please see the
	<a href="cxx_status.html">C++ status report page</a> to find out what is
	missing.</li>

	<li><b>StringRef'ize APIs</b>: A thankless but incredibly useful project is
	StringRef'izing (converting to use <tt>llvm::StringRef</tt> instead of <tt>const
	char *</tt> or <tt>std::string</tt>) various clang interfaces. This generally
	simplifies the code and makes it more efficient.</li>

	<li><b>Configuration Manager</b>: Clang/LLVM works on a large number of
	architectures and operating systems and can cross-compile to a similarly large
	number of configurations, but the pitfalls of choosing the command-line
	options, making sure the right sub-architecture is chosen and that the correct
	optional elements of your particular system can be a pain.

	<p>A tool that would investigate hosts and targets, and store the configuration
	in files that can later be used by Clang itself to avoid command-line options,
	especially the ones regarding which target options to use, would greatly alleviate
	this problem. A simple tool, with little or no dependency on LLVM itself, that
	will investigate a target architecture by probing hardware, software, libraries
	and compiling and executing code to identify all properties that would be relevant
	to command-line options (VFP, SSE, NEON, ARM vs. Thumb etc), triple settings etc.</p>

	<p>The first stage is to build a CFLAGS for Clang that would produce code on the
	current Host to the identified Target.</p>

	<p>The second stage would be to produce a configuration file (that can be used
	independently of the Host) so that Clang can read it and not need a gazillion
	of command-line options. Such file should be simple JSON / INI or anything that
	a text editor could change.</p></li>
	</ul>

	<p>If you hit a bug with Clang, it is very useful for us if you reduce the code
	that demonstrates the problem down to something small. There are many ways to
	do this; ask on <a href="https://discourse.llvm.org/c/clang">Discourse</a>,
	<a href="https://discord.com/channels/636084430946959380/636725486533345280">Discord</a>,
	or <a href="https://llvm.org/docs/GettingInvolved.html#irc"IRC</a> for advice.</p>

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