FASTBuild: generate compile_commands

If `CMAKE_EXPORT_COMPILE_COMMANDS` is set use FASTBuild's `-compdb`
option in order to generate `compile_commands.json` file.

Fixes: #27345

Source/cmGlobalFastbuildGenerator.cxx

@@ -477,11 +477,18 @@ void cmGlobalFastbuildGenerator::Generate()
       this->GetCMakeInstance()->GetIsInTryCompile()) {
     return;
   }
+  std::string const workingDir =
+    this->GetCMakeInstance()->GetHomeOutputDirectory();
   //  Make "rebuild-bff" target up-to-date after the generation.
   //  This is actually a noop, it just asks CMake to touch the generated file
   //  so FASTBuild would consider the target as up-to-date.
-  AskCMakeToMakeRebuildBFFUpToDate(
-    this->GetCMakeInstance()->GetHomeOutputDirectory());
+  AskCMakeToMakeRebuildBFFUpToDate(workingDir);
+
+  if (this->GlobalSettingIsOn("CMAKE_EXPORT_COMPILE_COMMANDS")) {
+    std::string output;
+    ExecuteFastbuildTarget(workingDir, FASTBUILD_ALL_TARGET_NAME, output,
+                           { "-compdb" });
+  }
 }
 
 void cmGlobalFastbuildGenerator::AskCMakeToMakeRebuildBFFUpToDate(

Tests/RunCMake/CMakeLists.txt

@@ -407,7 +407,7 @@ add_RunCMake_test(Configure -DMSVC_IDE=${MSVC_IDE})
 add_RunCMake_test(CpsExportImportBuild)
 add_RunCMake_test(CpsExportImportInstall)
 add_RunCMake_test(DisallowedCommands)
-if("${CMAKE_GENERATOR}" MATCHES "Unix Makefiles|Ninja")
+if("${CMAKE_GENERATOR}" MATCHES "Unix Makefiles|Ninja|FASTBuild")
   add_RunCMake_test(ExportCompileCommands)
 endif()
 add_RunCMake_test(ExcludeFromAll)

Tests/RunCMake/ExportCompileCommands/RunCMakeTest.cmake

@@ -9,4 +9,7 @@ endif()
 run_cmake_with_options(BeforeProject -DCMAKE_PROJECT_INCLUDE_BEFORE=BeforeProjectBEFORE.cmake)
 run_cmake(CustomCompileRule)
 run_cmake(Properties)
-run_cmake(PropertiesGenerateCommand)
+
+if(NOT RunCMake_GENERATOR STREQUAL "FASTBuild")
+  run_cmake(PropertiesGenerateCommand)
+endif()