CMAKE_EXPORT_COMPILE_COMMANDS: allow configuration per target

The new target property `EXPORT_COMPILE_COMMANDS` associated with the
existing global variable can be used to optionally configure targets for
their compile commands to be exported.

Fixes: #19462

Help/manual/cmake-properties.7.rst

@@ -196,6 +196,7 @@ Properties on Targets
    /prop_tgt/EXCLUDE_FROM_ALL
    /prop_tgt/EXCLUDE_FROM_DEFAULT_BUILD
    /prop_tgt/EXCLUDE_FROM_DEFAULT_BUILD_CONFIG
+   /prop_tgt/EXPORT_COMPILE_COMMANDS
    /prop_tgt/EXPORT_NAME
    /prop_tgt/EXPORT_PROPERTIES
    /prop_tgt/FOLDER

Help/prop_tgt/EXPORT_COMPILE_COMMANDS.rst

+EXPORT_COMPILE_COMMANDS
+-----------------------
+
+.. versionadded:: 3.20
+
+Enable/Disable output of compile commands during generation for a target.
+
+This property is initialized by the value of the variable
+:variable:`CMAKE_EXPORT_COMPILE_COMMANDS` if it is set when a target is created.

Help/release/dev/export-compile-commands-per-target.rst

+export-compile-commands-per-target
+----------------------------------
+
+* The :prop_tgt:`EXPORT_COMPILE_COMMANDS` target property was added
+  for the associated :variable:`CMAKE_EXPORT_COMPILE_COMMANDS` variable
+  to allow for configuration of exporting compile commands per target.

Help/variable/CMAKE_EXPORT_COMPILE_COMMANDS.rst

@@ -28,7 +28,8 @@ form.  The format of the JSON file looks like:
   ]
 
 This is initialized by the :envvar:`CMAKE_EXPORT_COMPILE_COMMANDS` environment
-variable.
+variable, and initializes the :prop_tgt:`EXPORT_COMPILE_COMMANDS` target
+property for all targets.
 
 .. note::
   This option is implemented only by :ref:`Makefile Generators`

Source/cmMakefileTargetGenerator.cxx

@@ -897,7 +897,7 @@ void cmMakefileTargetGenerator::WriteObjectRuleFiles(
       cmExpandList(compileRule, compileCommands);
     }
 
-    if (this->Makefile->IsOn("CMAKE_EXPORT_COMPILE_COMMANDS") &&
+    if (this->GeneratorTarget->GetPropertyAsBool("EXPORT_COMPILE_COMMANDS") &&
         lang_can_export_cmds && compileCommands.size() == 1) {
       std::string compileCommand = compileCommands[0];
 

Source/cmNinjaTargetGenerator.cxx

@@ -1532,7 +1532,7 @@ void cmNinjaTargetGenerator::ExportObjectCompileCommand(
   std::string const& objectFileDir, std::string const& flags,
   std::string const& defines, std::string const& includes)
 {
-  if (!this->Makefile->IsOn("CMAKE_EXPORT_COMPILE_COMMANDS")) {
+  if (!this->GeneratorTarget->GetPropertyAsBool("EXPORT_COMPILE_COMMANDS")) {
     return;
   }
 

Source/cmTarget.cxx

@@ -382,6 +382,7 @@ cmTarget::cmTarget(std::string const& name, cmStateEnums::TargetType type,
     initProp("UNITY_BUILD");
     initProp("UNITY_BUILD_UNIQUE_ID");
     initProp("OPTIMIZE_DEPENDENCIES");
+    initProp("EXPORT_COMPILE_COMMANDS");
     initPropValue("UNITY_BUILD_BATCH_SIZE", "8");
     initPropValue("UNITY_BUILD_MODE", "BATCH");
     initPropValue("PCH_WARN_INVALID", "ON");

Tests/RunCMake/ExportCompileCommands/Properties.cmake

+enable_language(C)
+
+add_library(Unset STATIC empty.c)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+add_library(SetOn STATIC empty.c)
+set(CMAKE_EXPORT_COMPILE_COMMANDS OFF)
+add_library(SetOff STATIC empty.c)
+
+get_property(_set TARGET Unset PROPERTY EXPORT_COMPILE_COMMANDS)
+if(_set)
+  message(SEND_ERROR "EXPORT_COMPILE_COMMANDS property should be unset for Unset target (got \"${_set}\")")
+endif()
+
+get_property(_on TARGET SetOn PROPERTY EXPORT_COMPILE_COMMANDS)
+if(NOT _on STREQUAL "ON")
+  message(SEND_ERROR "EXPORT_COMPILE_COMMANDS property should be \"ON\" for SetOn target (got \"${_on}\")")
+endif()
+
+get_property(_off TARGET SetOff PROPERTY EXPORT_COMPILE_COMMANDS)
+if(NOT _off STREQUAL "OFF")
+  message(SEND_ERROR "EXPORT_COMPILE_COMMANDS property should be \"OFF\" for SetOff target (got \"${_off}\")")
+endif()

Tests/RunCMake/ExportCompileCommands/PropertiesGenerateCommand-check.cmake

+if(NOT EXISTS "${RunCMake_TEST_BINARY_DIR}/compile_commands.json")
+  set(RunCMake_TEST_FAILED "compile_commands.json not generated")
+  return()
+endif()
+
+file(READ "${RunCMake_TEST_BINARY_DIR}/compile_commands.json" compile_commands)
+
+macro(check_error)
+  if(error)
+    message(SEND_ERROR "Unexpected error \"${error}\"\nFor: ${compile_commands}")
+  endif()
+endmacro()
+
+string(JSON num_commands ERROR_VARIABLE error LENGTH "${compile_commands}")
+check_error()
+
+# Only one of the targets has the EXPORT_COMPILE_COMMANDS property enabled.
+if(NOT num_commands STREQUAL 1)
+  message(SEND_ERROR "Expected 1 compile command, got ${num_commands} for ${compile_commands}")
+endif()
+
+# Get the compile command generated.
+string(JSON result ERROR_VARIABLE error GET "${compile_commands}" 0)
+check_error()
+string(JSON result ERROR_VARIABLE error GET "${result}" file)
+check_error()
+
+# And ensure the correct target is in that compile command.
+cmake_path(COMPARE "${result}" EQUAL "${RunCMake_TEST_SOURCE_DIR}/expected_file.c" good)
+if(NOT good)
+  message(SEND_ERROR "Expected \"${result}\" in \"${RunCMake_TEST_SOURCE_DIR}/expected_file.c\"")
+endif()

Tests/RunCMake/ExportCompileCommands/PropertiesGenerateCommand.cmake

+enable_language(C)
+
+add_library(Unset STATIC empty.c)
+add_library(ToBeSet STATIC expected_file.c)
+
+# Only one target with EXPORT_COMPILE_COMMANDS property.
+set_property(TARGET ToBeSet PROPERTY EXPORT_COMPILE_COMMANDS TRUE)

Tests/RunCMake/ExportCompileCommands/RunCMakeTest.cmake

 include(RunCMake)
 
+if(RunCMake_GENERATOR_IS_MULTI_CONFIG)
+  set(RunCMake_TEST_OPTIONS -DCMAKE_CONFIGURATION_TYPES=Debug)
+else()
+  set(RunCMake_TEST_OPTIONS -DCMAKE_BUILD_TYPE=Debug)
+endif()
+
 run_cmake_with_options(BeforeProject -DCMAKE_PROJECT_INCLUDE_BEFORE=BeforeProjectBEFORE.cmake)
 run_cmake(CustomCompileRule)
+run_cmake(Properties)
+run_cmake(PropertiesGenerateCommand)