Support checking out cte to 'extra' only as backward compatibility

[steveire]

Summary

This requirement to check it out in a directory called 'extra' was never
documented for git users, so git users doing the obvious thing (just
clone, don't specify a name) will silently not get clang-tools-extra
built.

Even reading the code is confusing because the
add_llvm_external_project macro appears to be used in place of the
add_subdirectory command, though the latter treats the second
placement argument as just a build directory name. So, anyone assuming
the same semantic with add_llvm_external_project would be confused.

[aaron.ballman]

Given the scope of what this changes (such as 3rd party configurations), I think that this requires a broader community discussion than what you'll get from this patch. I would suggest starting an [RFC] thread on cfe-commits and cfe-dev to see what people think of the idea.

Personally, I'm opposed to the idea. There is limited benefit compared to the number of scripts I will have to go update for out-of-tree builds where I'll suddenly be getting cmake warnings about a directory name that I've used without issue for years. If anything, I think the logic should be reversed so that we warn users who try to use "clang-tools-extra" as the directory name rather than "extra".

[steveire]

Will do!

tools/CMakeLists.txt

 
 if(CLANG_ENABLE_STATIC_ANALYZER)
   add_clang_subdirectory(clang-check)
   add_clang_subdirectory(clang-func-mapping)
   add_clang_subdirectory(scan-build)
   add_clang_subdirectory(scan-view)
 endif()
 
-# We support checking out the clang-tools-extra repository into the 'extra'
-# subdirectory. It contains tools developed as part of the Clang/LLVM project
-# on top of the Clang tooling platform. We keep them in a separate repository
-# to keep the primary Clang repository small and focused.
-# It also may be included by LLVM_EXTERNAL_CLANG_TOOLS_EXTRA_SOURCE_DIR.
+if (IS_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/extra)
+
+    # Documentation for working with SVN used to recommend using
+    # the name 'extra'.  Support that for now as backwards
+    # compatibility
+    message(DEPRECATION "Checking out clang-tools-extra into a directory called 'extra' is deprecated.
+Rename the directory to 'clang-tools-extra' instead.")
     add_llvm_external_project(clang-tools-extra extra)
+else()
+    add_llvm_external_project(clang-tools-extra)
+endif()
 
 # libclang may require clang-tidy in clang-tools-extra.
 add_clang_subdirectory(libclang)

www/get_started.html

<ul>
     <li><tt>svn co http://llvm.org/svn/llvm-project/cfe/trunk clang</tt></li>
     <li><tt>cd ../..</tt></li>
   </ul>
   </li>
   <li>Check out extra Clang tools: (optional)
   <ul>
     <li><tt>cd llvm/tools/clang/tools</tt></li>
     <li><tt>svn co http://llvm.org/svn/llvm-project/clang-tools-extra/trunk
-        extra</tt></li>
+        clang-tools-extra</tt></li>
     <li><tt>cd ../../../..</tt></li>
   </ul>
   </li>
   <li>Check out Compiler-RT (optional):
   <ul>
     <li><tt>cd llvm/projects</tt></li>
     <li><tt>svn co http://llvm.org/svn/llvm-project/compiler-rt/trunk
         compiler-rt</tt></li>