COMPILER_LAUNCHER: Add support for generator expressions

Fixes: #23441

Help/prop_tgt/LANG_COMPILER_LAUNCHER.rst

@@ -14,3 +14,8 @@ 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.
+
+.. versionadded:: 3.25
+
+  The property value may use
+  :manual:`generator expressions <cmake-generator-expressions(7)>`.

Help/release/dev/compiler-launcher-genexp.rst

@@ -0,0 +1,5 @@
+compiler-launcher-genexp
+------------------------
+
+* The :prop_tgt:`<LANG>_COMPILER_LAUNCHER` target property now supports
+  :manual:`generator expressions <cmake-generator-expressions(7)>`.

Source/cmMakefileTargetGenerator.cxx

@@ -1042,8 +1042,10 @@ void cmMakefileTargetGenerator::WriteObjectRuleFiles(
          lang == "OBJCXX")) {
       std::string const clauncher_prop = lang + "_COMPILER_LAUNCHER";
       cmValue clauncher = this->GeneratorTarget->GetProperty(clauncher_prop);
-      if (cmNonempty(clauncher)) {
-        compilerLauncher = *clauncher;
+      std::string evaluatedClauncher = cmGeneratorExpression::Evaluate(
+        *clauncher, this->LocalGenerator, config);
+      if (!evaluatedClauncher.empty()) {
+        compilerLauncher = evaluatedClauncher;
       }
     }
 

Source/cmNinjaTargetGenerator.cxx

@@ -912,8 +912,10 @@ void cmNinjaTargetGenerator::WriteCompileRule(const std::string& lang,
        lang == "OBJCXX")) {
     std::string const clauncher_prop = cmStrCat(lang, "_COMPILER_LAUNCHER");
     cmValue clauncher = this->GeneratorTarget->GetProperty(clauncher_prop);
-    if (cmNonempty(clauncher)) {
-      compilerLauncher = *clauncher;
+    std::string evaluatedClauncher = cmGeneratorExpression::Evaluate(
+      *clauncher, this->LocalGenerator, config);
+    if (!evaluatedClauncher.empty()) {
+      compilerLauncher = evaluatedClauncher;
     }
   }
 

Tests/RunCMake/CompilerLauncher/RunCMakeTest.cmake

@@ -17,7 +17,8 @@ endfunction()
 
 function(run_compiler_launcher_env lang)
   string(REGEX REPLACE "-.*" "" core_lang "${lang}")
-  set(ENV{CMAKE_${core_lang}_COMPILER_LAUNCHER} "${CMAKE_COMMAND};-E;env;USED_LAUNCHER=1")
+  # Use the noop genexp $<PATH:...> genexp to validate genexp support.
+  set(ENV{CMAKE_${core_lang}_COMPILER_LAUNCHER} "$<PATH:CMAKE_PATH,${CMAKE_COMMAND}>;-E;env;USED_LAUNCHER=1")
   run_compiler_launcher(${lang})
   unset(ENV{CMAKE_${core_lang}_COMPILER_LAUNCHER})
 endfunction()