cmake_language: Add EXIT subcommand

Add tests to cover these cases:

* run as regular CMake module, in NORMAL_MODE (expected to fail);
* run as CMake script in SCRIPT_MODE (expected to exit with given code);
* run as CMake script that `include()`-s another script with EXIT subcommand;
* run as CMake script which EVAL-uates EXIT subcommand via
  `cmake_language(EVAL CODE "<cmake code>")`.

Fixes: #23162

1 files changed, 26 insertions, 0 deletions

diff --git a/Source/cmCMakeLanguageCommand.cxx b/Source/cmCMakeLanguageCommand.cxx
index 329427c..9ffc363 100644
--- a/Source/cmCMakeLanguageCommand.cxx
+++ b/Source/cmCMakeLanguageCommand.cxx
@@ -398,6 +398,32 @@ bool cmCMakeLanguageCommand(std::vector<cmListFileArgument> const& args,
   if (!moreArgs()) {
     return FatalError(status, "called with incorrect number of arguments");
   }
+  if (expArgs[expArg] == "EXIT"_s) {
+    ++expArg; // consume "EXIT".
+
+    if (!moreArgs()) {
+      return FatalError(status, "EXIT requires one argument");
+    }
+
+    auto workingMode =
+      status.GetMakefile().GetCMakeInstance()->GetWorkingMode();
+    if (workingMode != cmake::SCRIPT_MODE) {
+      return FatalError(status, "EXIT can be used only in SCRIPT mode");
+    }
+
+    long retCode = 0;
+
+    if (!cmStrToLong(expArgs[expArg], &retCode)) {
+      return FatalError(status,
+                        cmStrCat("EXIT requires one integral argument, got \"",
+                                 expArgs[expArg], '\"'));
+    }
+
+    if (workingMode == cmake::SCRIPT_MODE) {
+      status.SetExitCode(static_cast<int>(retCode));
+    }
+    return true;
+  }
 
   if (expArgs[expArg] == "SET_DEPENDENCY_PROVIDER"_s) {
     finishArgs();