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  16 <h1>Open Clang Projects</h1>
  17
  18 <p>Here are a few tasks that are available for anyone to work on, depending
  19 on what your interests are. This list is provided to generate ideas, it is not
  20 intended to be comprehensive. Please ask on
  21 <a href="https://discourse.llvm.org/c/clang">Discourse</a> for more specifics
  22 or to verify that one of these isn't already completed.</p>
  23
  24 <ul>
  25 <li><b>Refresh and improve Clang's documentation</b>: Clang is inconsistent
  26 with documenting implementation-defined behaviors. We have significant
  27 documentation in the <a href="https://clang.llvm.org/docs/LanguageExtensions.html">
  28 Language Extensions</a> page, but the information is incomplete and the page is
  29 difficult to navigate. We would appreciate help with:
  30 <ul>
  31   <li>improving the way this information is presented to users,</li>
  32   <li><a href="https://llvm.org/docs/TableGen/">table generating</a>
  33       documentation where possible, such as for implementation limits or other
  34       target-specific information,</li>
  35   <li>adding documentation for currently
  36      <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/AttrDocs.td">
  37      undocumented attributes</a>,</li>
  38   <li>documenting <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/DiagnosticDocs.td">
  39       diagnostic group flags</a> (adding code examples of what is diagnosed, or
  40       other relevant information), or</li>
  41   <li>documenting <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Driver/Options.td">
  42       command line options</a>, or</li>
  43   <li>help with completing other missing documentation.</li>
  44 </ul>
  45 These projects are independent of each other.</li>
  46
  47 <li><b>Complete the investigation into Clang's C conformance</b>: Clang's
  48 <a href="c_status.html">C status page</a> contain a number of entries marked as
  49 <code>Unknown</code>. Completing the investigation involves adding
  50 <a href="https://github.com/llvm/llvm-project/tree/main/clang/test/C">test
  51 coverage</a> for the various standards papers and updating the documentation
  52 accordingly.
  53 </li>
  54
  55 <li><b>Improve Clang's C and C++ standard conformance test coverage</b>:
  56 Clang's test suite is structured such that most tests are written to provide
  57 coverage for what part of the compiler the feature's implementation exists in;
  58 we have parsing tests in <code>clang/test/Parser</code>, and semantic analysis
  59 tests in <code>clang/test/Sema*</code>, etc. We also have tests written to
  60 provide coverage for the standard requirements (<code>clang/test/CXX</code> and
  61 <code>clang/test/C</code>). The standards coverage is not structured in a way
  62 that makes it easy to maintain as the standards change over time. No commercial
  63 conformance test suite has a license model suitable for open source projects,
  64 so we would appreciate help in improving the existing coverage we have both in
  65 terms of layout of the tests as well as in coverage of the various standard
  66 modes.</li>
  67
  68 <li><b>Complete the investigation into Clang's C and C++ Defect Report
  69 conformance</b>: Separate from (but related to) general conformance testing is
  70 determining which <a href="c_dr_status.html">C defect reports</a> and
  71 <a href="cxx_dr_status.html">C++ defect reports</a> Clang implements. These
  72 lists currently have a number of entries marked as <code>Unknown</code>.
  73 Completing the investigation involves adding test coverage for
  74 <a href="https://github.com/llvm/llvm-project/tree/main/clang/test/C/drs">C</a>
  75 and
  76 <a href="https://github.com/llvm/llvm-project/tree/main/clang/test/CXX/drs">C++</a>
  77 defect reports and updating the documentation accordingly.</li>
  78
  79 <li><b>Bug triage</b>: Clang's <a href="https://github.com/llvm/llvm-project/issues">
  80 issue tracker</a>currently has over 20,000 open issues, many of which are not
  81 appropriately tagged, are no longer reproducible, could use a reduced test case,
  82 or otherwise needs some manual interaction. We can always use help with
  83 <a href="https://llvm.org/docs/BugLifeCycle.html#triaging-bugs">bug triage and
  84 issue tracker maintenance</a>.
  85 </li>
  86
  87 <li><b>Improve build times with Clang</b>: the time it takes Clang to process a
  88 translation unit is very important to our users; the lower the build time, the
  89 better the overall user experience. It would be good to improve Clang's
  90 performance as well as to find ways to proactively alert us when we've
  91 introduced a change that has significant negative impact on build times.</li>
  92
  93 <li><b>Complete support for the experimental constant expression interpreter
  94 </b>: Clang's production constant expression interpreter computes a constant
  95 expression result by walking over AST nodes, performing calculations as it
  96 goes. This does not have good performance properties, and so we've begun work
  97 on an <a href="https://clang.llvm.org/docs/ConstantInterpreter.html">
  98 experimental constant expression interpreter</a> that works by converting the
  99 AST into bytecode that is interpreted. This effort has a long tail of work left
 100 to complete because it requires implementing byte code for every kind of
 101 expression and type that can be used in a constant expression for C++ and C.
 102 </li>
 103
 104 <li><b>Improve clang-doc</b>: Clang's library-based design allows it to be used
 105 by a variety of tools that reason about source code.
 106 <a href="https://clang.llvm.org/extra/clang-doc.html">clang-doc</a> is one
 107 great application of this functionality, which generates code documentation
 108 from source code. The tool is in early stages of development and could use more
 109 dedicated effort to complete the implementation.</li>
 110
 111 <li><b>Self-testing using clang</b>: There are several neat ways to
 112 improve the quality of clang by self-testing. Some examples:
 113 <ul>
 114   <li>Improve the reliability of AST printing and serialization by
 115   ensuring that the AST produced by clang on an input doesn't change
 116   when it is reparsed or unserialized.
 117
 118   <li>Improve parser reliability and error generation by automatically
 119   or randomly changing the input checking that clang doesn't crash and
 120   that it doesn't generate excessive errors for small input
 121   changes. Manipulating the input at both the text and token levels is
 122   likely to produce interesting test cases.
 123 </ul>
 124 </li>
 125
 126 <li><b>Continue work on C++20, C++23, C++2c, and C23 support</b>:
 127   There are still several C++20 features to complete, and work has begun on
 128   supporting the latest language standards. Please see the
 129   <a href="cxx_status.html">C++ status report page</a> to find out what is
 130   missing.</li>
 131
 132 <li><b>StringRef'ize APIs</b>: A thankless but incredibly useful project is
 133 StringRef'izing (converting to use <tt>llvm::StringRef</tt> instead of <tt>const
 134 char *</tt> or <tt>std::string</tt>) various clang interfaces. This generally
 135 simplifies the code and makes it more efficient.</li>
 136
 137 <li><b>Configuration Manager</b>: Clang/LLVM works on a large number of
 138 architectures and operating systems and can cross-compile to a similarly large
 139 number of configurations, but the pitfalls of choosing the command-line
 140 options, making sure the right sub-architecture is chosen and that the correct
 141 optional elements of your particular system can be a pain.
 142
 143 <p>A tool that would investigate hosts and targets, and store the configuration
 144 in files that can later be used by Clang itself to avoid command-line options,
 145 especially the ones regarding which target options to use, would greatly alleviate
 146 this problem. A simple tool, with little or no dependency on LLVM itself, that
 147 will investigate a target architecture by probing hardware, software, libraries
 148 and compiling and executing code to identify all properties that would be relevant
 149 to command-line options (VFP, SSE, NEON, ARM vs. Thumb etc), triple settings etc.</p>
 150
 151 <p>The first stage is to build a CFLAGS for Clang that would produce code on the
 152 current Host to the identified Target.</p>
 153
 154 <p>The second stage would be to produce a configuration file (that can be used
 155 independently of the Host) so that Clang can read it and not need a gazillion
 156 of command-line options. Such file should be simple JSON / INI or anything that
 157 a text editor could change.</p></li>
 158 </ul>
 159
 160 <p>If you hit a bug with Clang, it is very useful for us if you reduce the code
 161 that demonstrates the problem down to something small. There are many ways to
 162 do this; ask on <a href="https://discourse.llvm.org/c/clang">Discourse</a>,
 163 <a href="https://discord.com/channels/636084430946959380/636725486533345280">Discord</a>,
 164 or <a href="https://llvm.org/docs/GettingInvolved.html#irc"IRC</a> for advice.</p>
 165
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