Add options to launch the compiler through tools like ccache or distcc

Create a <LANG>_COMPILER_LAUNCHER target property (initialized by a
CMAKE_<LANG>_COMPILER_LAUNCHER variable) to specify a compiler launcher
tool.  This will supersede the CMAKE_<LANG>_COMPILER_ARG1 approach to
using such tools.  The old approach set CMAKE_<LANG>_COMPILER to the
launcher tool while the new approach leaves this variable set to the
actual compiler.

Implement this property for Makefile and Ninja generators.  It cannot be
implemented for VS or Xcode generators as the IDE build tools offer no
such hooks.

Help/manual/cmake-properties.7.rst

@@ -177,6 +177,7 @@ Properties on Targets
    /prop_tgt/JOB_POOL_COMPILE
    /prop_tgt/JOB_POOL_LINK
    /prop_tgt/LABELS
+   /prop_tgt/LANG_COMPILER_LAUNCHER
    /prop_tgt/LANG_INCLUDE_WHAT_YOU_USE
    /prop_tgt/LANG_VISIBILITY_PRESET
    /prop_tgt/LIBRARY_OUTPUT_DIRECTORY_CONFIG

Help/manual/cmake-variables.7.rst

@@ -235,6 +235,7 @@ Variables that Control the Build
    /variable/CMAKE_INSTALL_NAME_DIR
    /variable/CMAKE_INSTALL_RPATH
    /variable/CMAKE_INSTALL_RPATH_USE_LINK_PATH
+   /variable/CMAKE_LANG_COMPILER_LAUNCHER
    /variable/CMAKE_LANG_INCLUDE_WHAT_YOU_USE
    /variable/CMAKE_LANG_VISIBILITY_PRESET
    /variable/CMAKE_LIBRARY_OUTPUT_DIRECTORY

Help/prop_tgt/LANG_COMPILER_LAUNCHER.rst

@@ -0,0 +1,13 @@
+<LANG>_COMPILER_LAUNCHER
+------------------------
+
+This property is implemented only when ``<LANG>`` is ``C`` or ``CXX``.
+
+Specify a :ref:`;-list <CMake Language Lists>` containing a command line
+for a compiler launching tool. The :ref:`Makefile Generators` and the
+:generator:`Ninja` generator will run this tool and pass the compiler and
+its arguments to the tool. Some example tools are distcc and ccache.
+
+This property is initialized by the value of
+the :variable:`CMAKE_<LANG>_COMPILER_LAUNCHER` variable if it is set
+when a target is created.

Help/release/dev/compiler-launcher.rst

@@ -0,0 +1,8 @@
+compiler-launcher
+-----------------
+
+* The :ref:`Makefile Generators` and the :generator:`Ninja` generator
+  learned to add compiler launcher tools like distcc and ccache along with the
+  compiler for ``C`` and ``CXX`` languages.  See the
+  :variable:`CMAKE_<LANG>_COMPILER_LAUNCHER` variable and
+  :prop_tgt:`<LANG>_COMPILER_LAUNCHER` target property for details.

Help/variable/CMAKE_LANG_COMPILER_LAUNCHER.rst

@@ -0,0 +1,6 @@
+CMAKE_<LANG>_COMPILER_LAUNCHER
+------------------------------
+
+Default value for :prop_tgt:`<LANG>_COMPILER_LAUNCHER` target property.
+This variable is used to initialize the property on each target as it is
+created.  This is done only when ``<LANG>`` is ``C`` or ``CXX``.

Source/cmMakefileTargetGenerator.cxx

@@ -775,6 +775,25 @@ cmMakefileTargetGenerator
       }
     }
 
+  // Maybe insert a compiler launcher like ccache or distcc
+  if (!compileCommands.empty() && (lang == "C" || lang == "CXX"))
+    {
+    std::string const clauncher_prop = lang + "_COMPILER_LAUNCHER";
+    const char *clauncher = this->Target->GetProperty(clauncher_prop);
+    if (clauncher && *clauncher)
+      {
+      std::vector<std::string> launcher_cmd;
+      cmSystemTools::ExpandListArgument(clauncher, launcher_cmd, true);
+      for (std::vector<std::string>::iterator i = launcher_cmd.begin(),
+             e = launcher_cmd.end(); i != e; ++i)
+        {
+        *i = this->LocalGenerator->EscapeForShell(*i);
+        }
+      std::string const& run_launcher = cmJoin(launcher_cmd, " ") + " ";
+      compileCommands.front().insert(0, run_launcher);
+      }
+    }
+
   // Expand placeholders in the commands.
   for(std::vector<std::string>::iterator i = compileCommands.begin();
       i != compileCommands.end(); ++i)

Source/cmNinjaTargetGenerator.cxx

@@ -22,6 +22,7 @@
 #include "cmComputeLinkInformation.h"
 #include "cmSourceFile.h"
 #include "cmCustomCommandGenerator.h"
+#include "cmAlgorithms.h"
 
 #include <algorithm>
 
@@ -475,6 +476,25 @@ cmNinjaTargetGenerator
       }
     }
 
+  // Maybe insert a compiler launcher like ccache or distcc
+  if (!compileCmds.empty() && (lang == "C" || lang == "CXX"))
+    {
+    std::string const clauncher_prop = lang + "_COMPILER_LAUNCHER";
+    const char *clauncher = this->Target->GetProperty(clauncher_prop);
+    if (clauncher && *clauncher)
+      {
+      std::vector<std::string> launcher_cmd;
+      cmSystemTools::ExpandListArgument(clauncher, launcher_cmd, true);
+      for (std::vector<std::string>::iterator i = launcher_cmd.begin(),
+             e = launcher_cmd.end(); i != e; ++i)
+        {
+        *i = this->LocalGenerator->EscapeForShell(*i);
+        }
+      std::string const& run_launcher = cmJoin(launcher_cmd, " ") + " ";
+      compileCmds.front().insert(0, run_launcher);
+      }
+    }
+
   if (!compileCmds.empty())
     {
     compileCmds.front().insert(0, cldeps);

Source/cmTarget.cxx

@@ -333,10 +333,12 @@ void cmTarget::SetMakefile(cmMakefile* mf)
     this->SetPropertyDefault("MACOSX_BUNDLE", 0);
     this->SetPropertyDefault("MACOSX_RPATH", 0);
     this->SetPropertyDefault("NO_SYSTEM_FROM_IMPORTED", 0);
+    this->SetPropertyDefault("C_COMPILER_LAUNCHER", 0);
     this->SetPropertyDefault("C_INCLUDE_WHAT_YOU_USE", 0);
     this->SetPropertyDefault("C_STANDARD", 0);
     this->SetPropertyDefault("C_STANDARD_REQUIRED", 0);
     this->SetPropertyDefault("C_EXTENSIONS", 0);
+    this->SetPropertyDefault("CXX_COMPILER_LAUNCHER", 0);
     this->SetPropertyDefault("CXX_INCLUDE_WHAT_YOU_USE", 0);
     this->SetPropertyDefault("CXX_STANDARD", 0);
     this->SetPropertyDefault("CXX_STANDARD_REQUIRED", 0);

Tests/RunCMake/CMakeLists.txt

@@ -232,4 +232,5 @@ endif()
 if("${CMAKE_GENERATOR}" MATCHES "Make|Ninja")
   add_executable(pseudo_iwyu pseudo_iwyu.c)
   add_RunCMake_test(IncludeWhatYouUse -DPSEUDO_IWYU=$<TARGET_FILE:pseudo_iwyu>)
+  add_RunCMake_test(CompilerLauncher)
 endif()

Tests/RunCMake/CompilerLauncher/C-Build-stdout.txt

@@ -0,0 +1 @@
+.*-E env USED_LAUNCHER=1.*

Tests/RunCMake/CompilerLauncher/C-launch-Build-stdout.txt

@@ -0,0 +1 @@
+.*-E env USED_LAUNCHER=1.*

Tests/RunCMake/CompilerLauncher/C-launch.cmake

@@ -0,0 +1,3 @@
+set(CTEST_USE_LAUNCHERS 1)
+include(CTestUseLaunchers)
+include(C.cmake)

Tests/RunCMake/CompilerLauncher/C.cmake

@@ -0,0 +1,4 @@
+enable_language(C)
+set(CMAKE_C_COMPILER_LAUNCHER "${CMAKE_COMMAND};-E;env;USED_LAUNCHER=1")
+set(CMAKE_VERBOSE_MAKEFILE TRUE)
+add_executable(main main.c)

Tests/RunCMake/CompilerLauncher/CMakeLists.txt

@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.2)
+project(${RunCMake_TEST} NONE)
+include(${RunCMake_TEST}.cmake)

Tests/RunCMake/CompilerLauncher/CXX-Build-stdout.txt

@@ -0,0 +1 @@
+.*-E env USED_LAUNCHER=1.*

Tests/RunCMake/CompilerLauncher/CXX-launch-Build-stdout.txt

@@ -0,0 +1 @@
+.*-E env USED_LAUNCHER=1.*

Tests/RunCMake/CompilerLauncher/CXX-launch.cmake

@@ -0,0 +1,3 @@
+set(CTEST_USE_LAUNCHERS 1)
+include(CTestUseLaunchers)
+include(CXX.cmake)

Tests/RunCMake/CompilerLauncher/CXX.cmake

@@ -0,0 +1,4 @@
+enable_language(CXX)
+set(CMAKE_CXX_COMPILER_LAUNCHER "${CMAKE_COMMAND};-E;env;USED_LAUNCHER=1")
+set(CMAKE_VERBOSE_MAKEFILE TRUE)
+add_executable(main main.cxx)

Tests/RunCMake/CompilerLauncher/RunCMakeTest.cmake

@@ -0,0 +1,23 @@
+include(RunCMake)
+
+function(run_compiler_launcher lang)
+  # Use a single build tree for tests without cleaning.
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/${lang}-build)
+  set(RunCMake_TEST_NO_CLEAN 1)
+  file(REMOVE_RECURSE "${RunCMake_TEST_BINARY_DIR}")
+  file(MAKE_DIRECTORY "${RunCMake_TEST_BINARY_DIR}")
+  run_cmake(${lang})
+
+  set(RunCMake_TEST_OUTPUT_MERGE 1)
+  if("${RunCMake_GENERATOR}" STREQUAL "Ninja")
+    set(verbose_args -- -v)
+  endif()
+  run_cmake_command(${lang}-Build ${CMAKE_COMMAND} --build . ${verbose_args})
+endfunction()
+
+run_compiler_launcher(C)
+run_compiler_launcher(CXX)
+if (NOT RunCMake_GENERATOR STREQUAL "Watcom WMake")
+  run_compiler_launcher(C-launch)
+  run_compiler_launcher(CXX-launch)
+endif()

Tests/RunCMake/CompilerLauncher/main.c

@@ -0,0 +1,3 @@
+int main(void) {
+  return 0;
+}

Tests/RunCMake/CompilerLauncher/main.cxx

@@ -0,0 +1 @@
+int main() { return 0; }