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Using `sccache` with Xcode

docs/Xcode.md

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Using sccache with Xcode

It is possible to use sccache with Xcode with some setup.

Running the daemon

Before building, you need to run the daemon outside of Xcode. This needs to be done because if sccache invocation happens to implicitly start the server daemon, the Xcode build will hang on the sccache invocation, waiting for the process to idle timeout.

You can do this in another terminal windows by calling

sh
SCCACHE_LOG=info SCCACHE_START_SERVER=1 SCCACHE_NO_DAEMON=1 sccache

Or by setting it up in a launchd configuration, perhaps as ~/Library/LaunchAgents/sccache.plist (note the paths in the plist):

xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>Label</key>
    <string>sccache.server</string>
    <key>ProgramArguments</key>
    <array>
      <string>/path/to/sccache</string>
    </array>
    <key>EnvironmentVariables</key>
    <dict>
        <key>SCCACHE_START_SERVER</key>
        <string>1</string>
        <key>SCCACHE_NO_DAEMON</key>
        <string>1</string>
        <key>SCCACHE_IDLE_TIMEOUT</key>
        <string>0</string>
        <key>SCCACHE_LOG</key>
        <string>info</string>
    </dict>

    <key>StandardOutPath</key>
    <string>/tmp/sccache.log</string>
    <key>StandardErrorPath</key>
    <string>/tmp/sccache.log</string>

  </dict>
</plist>

Setting it up for xcodebuild

Xcode seems to support barely documented C_COMPILER_LAUNCHER attribute, for having a custom launcher program.

Then you can invoke xcodebuild like so

sh
xcodebuild C_COMPILER_LAUNCHER=sccache
           CLANG_ENABLE_MODULES=NO
           COMPILER_INDEX_STORE_ENABLE=NO
           CLANG_USE_RESPONSE_FILE=NO

Where the additional arguments are for disabling some features that sccache can't cache currently.

These build settings can also be put in a xcconfig file, like sccache.xcconfig

C_COMPILER_LAUNCHER=sccache
CLANG_ENABLE_MODULES=NO
COMPILER_INDEX_STORE_ENABLE=NO
CLANG_USE_RESPONSE_FILE=NO

Which can then be invoked with

sh
xcodebuild -xcconfig sccache.xcconfig

Setting it up for cmake Xcode generator

While cmake has the convenient CMAKE_<LANG>_COMPILER_LAUNCHER for prepending tools like sccache, it is not supported for the Xcode generator.

But you can configuring it directly with something like

cmake

# This bit before the first `project()`, as the COMPILER_LAUNCHER variables are read in then
if(DEFINED CCACHE)
    find_program(CCACHE_EXE ${CCACHE} REQUIRED)
    if(NOT CMAKE_GENERATOR STREQUAL "Xcode")
        # Support for other generators should work with these
        set(CMAKE_C_COMPILER_LAUNCHER "${CCACHE_EXE}")
        set(CMAKE_CXX_COMPILER_LAUNCHER "${CCACHE_EXE}")
    else()
        # And this should work for Xcode generator
        set(CMAKE_XCODE_ATTRIBUTE_C_COMPILER_LAUNCHER ${CCACHE_EXE})
        set(CMAKE_XCODE_ATTRIBUTE_CLANG_ENABLE_MODULES "NO")
        set(CMAKE_XCODE_ATTRIBUTE_COMPILER_INDEX_STORE_ENABLE "NO")
        set(CMAKE_XCODE_ATTRIBUTE_CLANG_USE_RESPONSE_FILE "NO")
    endif()
endif()

Then configuring with -DCCACHE=sccache should work on all generators.