youcompleteme: fix compilation

1) Replace --system-libclang with an explicit setting for the path to
nix libclang 3.9. Otherwise it will find system's libclang on darwin.

2) Remove clang/llvm from build inputs. This prevents ycm itself from
being compiled by clang 3.9. stdenv's standard compiler (gcc or
clang 3.7) will suffice.

3) Enable C++11 again as #16212 is caused by incopatibility between
clang 3.9 and libc++ 3.7, but we don't compile YCM with clang 3.9, so
this is not needed anymore.

pkgs/misc/vim-plugins/default.nix

@@ -1309,17 +1309,18 @@ rec {
     dependencies = [];
     buildInputs = [
       python go cmake
-      (if stdenv.isDarwin then llvmPackages.clang else llvmPackages.clang-unwrapped)
-      llvmPackages.llvm
     ] ++ stdenv.lib.optional stdenv.isDarwin Cocoa;
 
     propagatedBuildInputs = stdenv.lib.optional (!stdenv.isDarwin) rustracerd;
 
     patches = [
-      ./patches/youcompleteme/1-top-cmake.patch
       ./patches/youcompleteme/2-ycm-cmake.patch
     ];
 
+    # YCM requires path to external libclang 3.9
+    # For explicit use and as env variable for ../third_party/ycmd/build.py
+    EXTRA_CMAKE_ARGS="-DEXTERNAL_LIBCLANG_PATH=${llvmPackages.clang.cc}/lib/libclang.${if stdenv.isDarwin then "dylib" else "so"}";
+
     buildPhase = ''
       patchShebangs .
       substituteInPlace plugin/youcompleteme.vim \
@@ -1327,9 +1328,10 @@ rec {
 
       mkdir build
       pushd build
-      cmake -G "Unix Makefiles" . ../third_party/ycmd/cpp -DPYTHON_LIBRARIES:PATH=${python}/lib/libpython2.7.so -DPYTHON_INCLUDE_DIR:PATH=${python}/include/python2.7 -DUSE_CLANG_COMPLETER=ON -DUSE_SYSTEM_LIBCLANG=ON
+      cmake -G "Unix Makefiles" . ../third_party/ycmd/cpp -DPYTHON_LIBRARIES:PATH=${python}/lib/libpython2.7.so -DPYTHON_INCLUDE_DIR:PATH=${python}/include/python2.7 -DUSE_CLANG_COMPLETER=ON \
+        $EXTRA_CMAKE_ARGS
       make ycm_core -j''${NIX_BUILD_CORES} -l''${NIX_BUILD_CORES}}
-      ${python}/bin/python ../third_party/ycmd/build.py --gocode-completer --clang-completer --system-libclang
+      ${python}/bin/python ../third_party/ycmd/build.py --gocode-completer --clang-completer
       popd
     '';
 

pkgs/misc/vim-plugins/patches/youcompleteme/1-top-cmake.patch

@@ -1,14 +0,0 @@
-
---- ./third_party/ycmd/cpp/CMakeLists.txt
-+++ ./third_party/ycmd/cpp/CMakeLists.txt
-@@ -121,8 +121,8 @@
-     set( CPP11_AVAILABLE true )
-   endif()
- elseif( COMPILER_IS_CLANG )
--  set( CPP11_AVAILABLE true )
--  set( CMAKE_XCODE_ATTRIBUTE_CLANG_CXX_LANGUAGE_STANDARD "c++11" )
-+  #set( CPP11_AVAILABLE true )
-+  #  set( CMAKE_XCODE_ATTRIBUTE_CLANG_CXX_LANGUAGE_STANDARD "c++11" )
-   set( CMAKE_XCODE_ATTRIBUTE_CLANG_CXX_LIBRARY "libc++" )
- endif()
- 

pkgs/misc/vim-plugins/vim2nix/additional-nix-code/youcompleteme

@@ -1,16 +1,17 @@
     buildInputs = [
       python go cmake
-      (if stdenv.isDarwin then llvmPackages.clang else llvmPackages.clang-unwrapped)
-      llvmPackages.llvm
     ] ++ stdenv.lib.optional stdenv.isDarwin Cocoa;
 
     propagatedBuildInputs = stdenv.lib.optional (!stdenv.isDarwin) rustracerd;
 
     patches = [
-      ./patches/youcompleteme/1-top-cmake.patch
       ./patches/youcompleteme/2-ycm-cmake.patch
     ];
 
+    # YCM requires path to external libclang 3.9
+    # For explicit use and as env variable for ../third_party/ycmd/build.py
+    EXTRA_CMAKE_ARGS="-DEXTERNAL_LIBCLANG_PATH=${llvmPackages.clang.cc}/lib/libclang.${if stdenv.isDarwin then "dylib" else "so"}";
+
     buildPhase = ''
       patchShebangs .
       substituteInPlace plugin/youcompleteme.vim \
@@ -18,9 +19,10 @@
 
       mkdir build
       pushd build
-      cmake -G "Unix Makefiles" . ../third_party/ycmd/cpp -DPYTHON_LIBRARIES:PATH=${python}/lib/libpython2.7.so -DPYTHON_INCLUDE_DIR:PATH=${python}/include/python2.7 -DUSE_CLANG_COMPLETER=ON -DUSE_SYSTEM_LIBCLANG=ON
+      cmake -G "Unix Makefiles" . ../third_party/ycmd/cpp -DPYTHON_LIBRARIES:PATH=${python}/lib/libpython2.7.so -DPYTHON_INCLUDE_DIR:PATH=${python}/include/python2.7 -DUSE_CLANG_COMPLETER=ON \
+        $EXTRA_CMAKE_ARGS
       make ycm_core -j''${NIX_BUILD_CORES} -l''${NIX_BUILD_CORES}}
-      ${python}/bin/python ../third_party/ycmd/build.py --gocode-completer --clang-completer --system-libclang
+      ${python}/bin/python ../third_party/ycmd/build.py --gocode-completer --clang-completer
       popd
     '';