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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I can wait to see what you propose for actual coding-standard wording, as guidance for figuring out layering.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></a></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> David Blaikie [mailto:dblaikie@gmail.com]
<br>
<b>Sent:</b> Wednesday, January 17, 2018 11:30 AM<br>
<b>To:</b> Robinson, Paul<br>
<b>Cc:</b> Richard Smith; Chandler Carruth; Reid Kleckner; llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] Layering Requirements in the LLVM Coding Style Guide<o:p></o:p></span></p>
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<p class="MsoNormal">On Wed, Jan 17, 2018 at 11:25 AM Robinson, Paul <<a href="mailto:paul.robinson@sony.com">paul.robinson@sony.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Looking at build-procedure files for link-order hints is technically "written down" but not really
human-friendly and not at all what I had in mind. </span><span style="font-size:11.0pt;font-family:Wingdings;color:#1F497D">J</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><a name="m_119641913190225571__MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I get that writing it down on a doc page will have
the usual bit-rot problems, but if you want to tell developers (especially newer developers) "get the layering right" you really need to point to a place that says what the layering *is*. Maybe you were agreeing to do that, but I'm not sure.</span><o:p></o:p></a></p>
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I wasn't planning on writing it down anymore than it's already necessarily enshrined in the build system. I'm not expecting to yell at/complain to people who violate it unknowingly (Apple/Windows developers in general don't get layering checked today because
their linkers do resolve circular dependencies - but they get failures on Linux buildbots and fix them when they arise) - but to point out "oh, hey, maybe you didn't notice but this introduces a layering violation - please fix it".<br>
<br>
I'm not sure what makes LLVMBuild.txt not human-friendly - they're very terse text files, contain little other than a list of dependencies. They're probably easier to read/maintain than CMakeLists.txt which have to be updated whenever a new source file is added.
These lists have to be updated/maintained when new libraries or dependencies are introduced & yeah, for the most part we don't have to think about them - and most changes won't impact layering/violate layering constraints, but then rarely we will hit these
things & check or update the layering, etc.<br>
<br>
- Dave<br>
<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I have found layering to be a particularly useful and beneficial model in past large software projects.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Is LLVM's layering actually written down anywhere? Last time I went looking, there was nothing.
If there's no spec, there's no verifiable conformance; you have to guess based on what other files do.</span><o:p></o:p></p>
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<br>
Fair point - Google's build system is pretty specific about this & so we've got it codified there, and the open source build system has to know some of this to get the link order right - otherwise LLVM programs couldn't successfully link (if the libraries weren't
placed in the right order on the link command)<br>
<br>
I think the the LLVMBuild.txt files contain the library dependency lists for the CMake build.<br>
<br>
- Dave<br>
<o:p></o:p></p>
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