[lldb][CMake] Generating Xcode projects

[sgraenitz]

Summary

Print a warning if the wrong cache script is used when generating a Xcode project, because it's too easy to confuse with Apple-lldb-macOS.cmake

When building with Xcode, we recommend using the corresponding cache
script.  If this was a mistake, clean your lean build directory and re-run
CMake with:

  -C /path/to/llvm-project/lldb/cmake/caches/Apple-lldb-Xcode.cmake

See: https://lldb.llvm.org/resources/build.html#cmakegeneratedxcodeproject

Also set the generator inside the cache script.

[JDevlieghere]

Small comment about the working, but the change itself LGTM.

lldb/cmake/modules/LLDBConfig.cmake

77

[bikeshedding] I think we should say something like:

When building with Xcode, we recommend using the corresponding cache script. If this was a mistake, clean your lean your build directory and re-run CMake with:

[sgraenitz]

Improve warning message

[jingham]

Thanks for doing this. Looks okay to me just one typo... But I don't know CMake well enough to comment on substance...

lldb/cmake/modules/LLDBConfig.cmake

78

This should work not just for Jack Spratt but also his wife! "LEAN build directory"

lldb/cmake/caches/Apple-lldb-Xcode.cmake

 include(${CMAKE_CURRENT_LIST_DIR}/Apple-lldb-base.cmake)
 
-set(LLDB_BUILD_FRAMEWORK ON CACHE BOOL "")
+set(CMAKE_GENERATOR Xcode)
 set(CMAKE_OSX_DEPLOYMENT_TARGET 10.11 CACHE STRING "")
 set(CMAKE_XCODE_GENERATE_SCHEME ON CACHE BOOL "")
+
+set(LLDB_BUILD_FRAMEWORK ON CACHE BOOL "")
+
+# Print a warning with instructions, if we
+# build with Xcode and didn't use this cache.
+set(LLDB_EXPLICIT_XCODE_CACHE_USED ON CACHE INTERNAL "")

lldb/cmake/modules/LLDBConfig.cmake

if(LLDB_BUILD_FRAMEWORK)
   set(LLDB_FRAMEWORK_BUILD_DIR bin CACHE STRING "Output directory for LLDB.framework")
   set(LLDB_FRAMEWORK_INSTALL_DIR Library/Frameworks CACHE STRING "Install directory for LLDB.framework")
 
   # Essentially, emit the framework's dSYM outside of the framework directory.
   set(LLDB_DEBUGINFO_INSTALL_PREFIX ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin CACHE STRING
       "Directory to emit dSYM files stripped from executables and libraries (Darwin Only)")
 endif()
 
+if(APPLE AND CMAKE_GENERATOR STREQUAL Xcode)
+  if(NOT LLDB_EXPLICIT_XCODE_CACHE_USED)
+    message(WARNING
+      "When building with Xcode, we recommend using the corresponding cache script. "
+      "If this was a mistake, clean your lean build directory and re-run CMake with:\n"
+      "  -C ${CMAKE_SOURCE_DIR}/cmake/caches/Apple-lldb-Xcode.cmake\n"
+      "See: https://lldb.llvm.org/resources/build.html#cmakegeneratedxcodeproject\n")
+  endif()
+endif()
+
 if (NOT CMAKE_SYSTEM_NAME MATCHES "Windows")
   set(LLDB_EXPORT_ALL_SYMBOLS 0 CACHE BOOL
     "Causes lldb to export all symbols when building liblldb.")
 else()
   # Windows doesn't support toggling this, so don't bother making it a
   # cache variable.
   set(LLDB_EXPORT_ALL_SYMBOLS 0)
 endif()

lldb/docs/resources/build.rst

::
   > git clone https://github.com/llvm/llvm-project
 
   > cmake -B /path/to/llvm-build -G Ninja \
           -C /path/to/llvm-project/lldb/cmake/caches/Apple-lldb-base.cmake \
           -DLLVM_ENABLE_PROJECTS="clang;libcxx" \
           llvm-project/llvm
   > ninja -C /path/to/llvm-build
 
-  > cmake -B /path/to/lldb-build -G Xcode \
+  > cmake -B /path/to/lldb-build \
           -C /path/to/llvm-project/lldb/cmake/caches/Apple-lldb-Xcode.cmake \
           -DLLVM_DIR=/path/to/llvm-build/lib/cmake/llvm \
           -DClang_DIR=/path/to/llvm-build/lib/cmake/clang \
           llvm-project/lldb
   > open lldb.xcodeproj
   > cmake --build /path/to/lldb-build --target check-lldb
 
 .. note::