EXPORT_PACKAGE_DEPENDENCIES: Add experimental feature gate

Some design concerns have been raised after trying the 3.29 release
candidates.  Avoid committing to a stable public interface for now.

Issue: #25767

4 files changed, 30 insertions, 5 deletions

diff --git a/Source/cmExperimental.cxx b/Source/cmExperimental.cxx
index d75879f..fb21f53 100644
--- a/Source/cmExperimental.cxx
+++ b/Source/cmExperimental.cxx
@@ -19,6 +19,15 @@ namespace {
  * up-to-date.
  */
 cmExperimental::FeatureData LookupTable[] = {
+  // ExportPackageDependencies
+  { "ExportPackageDependencies",
+    "1942b4fa-b2c5-4546-9385-83f254070067",
+    "CMAKE_EXPERIMENTAL_EXPORT_PACKAGE_DEPENDENCIES",
+    "CMake's EXPORT_PACKAGE_DEPENDENCIES support is experimental. It is meant "
+    "only for experimentation and feedback to CMake developers.",
+    {},
+    cmExperimental::TryCompileCondition::Always,
+    false },
   // WindowsKernelModeDriver
   { "WindowsKernelModeDriver",
     "5c2d848d-4efa-4529-a768-efd57171bf68",
diff --git a/Source/cmExperimental.h b/Source/cmExperimental.h
index e4c1448..5593c85 100644
--- a/Source/cmExperimental.h
+++ b/Source/cmExperimental.h
@@ -15,6 +15,7 @@ class cmExperimental
 public:
   enum class Feature
   {
+    ExportPackageDependencies,
     WindowsKernelModeDriver,
 
     Sentinel,
diff --git a/Source/cmExportCommand.cxx b/Source/cmExportCommand.cxx
index 7d23c91..0cb0011 100644
--- a/Source/cmExportCommand.cxx
+++ b/Source/cmExportCommand.cxx
@@ -17,6 +17,7 @@
 #include "cmArgumentParserTypes.h"
 #include "cmCryptoHash.h"
 #include "cmExecutionStatus.h"
+#include "cmExperimental.h"
 #include "cmExportBuildAndroidMKGenerator.h"
 #include "cmExportBuildFileGenerator.h"
 #include "cmExportSet.h"
@@ -83,12 +84,20 @@ bool cmExportCommand(std::vector<std::string> const& args,
       .Bind("CXX_MODULES_DIRECTORY"_s, &Arguments::CxxModulesDirectory);
 
   if (args[0] == "EXPORT") {
-    parser.Bind("EXPORT"_s, &Arguments::ExportSetName)
-      .Bind("EXPORT_PACKAGE_DEPENDENCIES"_s,
-            &Arguments::ExportPackageDependencies);
+    parser.Bind("EXPORT"_s, &Arguments::ExportSetName);
+    if (cmExperimental::HasSupportEnabled(
+          status.GetMakefile(),
+          cmExperimental::Feature::ExportPackageDependencies)) {
+      parser.Bind("EXPORT_PACKAGE_DEPENDENCIES"_s,
+                  &Arguments::ExportPackageDependencies);
+    }
   } else if (args[0] == "SETUP") {
     parser.Bind("SETUP"_s, &Arguments::ExportSetName);
-    parser.Bind("PACKAGE_DEPENDENCY"_s, &Arguments::PackageDependencyArgs);
+    if (cmExperimental::HasSupportEnabled(
+          status.GetMakefile(),
+          cmExperimental::Feature::ExportPackageDependencies)) {
+      parser.Bind("PACKAGE_DEPENDENCY"_s, &Arguments::PackageDependencyArgs);
+    }
     parser.Bind("TARGET"_s, &Arguments::TargetArgs);
   } else {
     parser.Bind("TARGETS"_s, &Arguments::Targets);
diff --git a/Source/cmInstallCommand.cxx b/Source/cmInstallCommand.cxx
index e2755da..1567629 100644
--- a/Source/cmInstallCommand.cxx
+++ b/Source/cmInstallCommand.cxx
@@ -21,6 +21,7 @@
 #include "cmArgumentParser.h"
 #include "cmArgumentParserTypes.h"
 #include "cmExecutionStatus.h"
+#include "cmExperimental.h"
 #include "cmExportSet.h"
 #include "cmFileSet.h"
 #include "cmGeneratorExpression.h"
@@ -2061,7 +2062,12 @@ bool HandleExportMode(std::vector<std::string> const& args,
   ica.Bind("EXPORT_LINK_INTERFACE_LIBRARIES"_s, exportOld);
   ica.Bind("FILE"_s, filename);
   ica.Bind("CXX_MODULES_DIRECTORY"_s, cxx_modules_directory);
-  ica.Bind("EXPORT_PACKAGE_DEPENDENCIES"_s, exportPackageDependencies);
+
+  if (cmExperimental::HasSupportEnabled(
+        status.GetMakefile(),
+        cmExperimental::Feature::ExportPackageDependencies)) {
+    ica.Bind("EXPORT_PACKAGE_DEPENDENCIES"_s, exportPackageDependencies);
+  }
 
   std::vector<std::string> unknownArgs;
   ica.Parse(args, &unknownArgs);