cmExperimental: add a mechanism for experimental CMake features

1 files changed, 56 insertions, 0 deletions

diff --git a/Source/cmExperimental.cxx b/Source/cmExperimental.cxx
new file mode 100644
index 0000000000..5689714f1f
--- /dev/null
+++ b/Source/cmExperimental.cxx
@@ -0,0 +1,56 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+
+#include "cmExperimental.h"
+
+#include <cassert>
+#include <cstddef>
+#include <string>
+
+#include "cmMakefile.h"
+#include "cmMessageType.h"
+#include "cmValue.h"
+
+namespace {
+
+/*
+ * The `Uuid` fields of these objects should change periodically.
+ * Search for other instances to keep the documentation and test suite
+ * up-to-date.
+ */
+
+struct FeatureData
+{
+  std::string const Uuid;
+  std::string const Variable;
+  std::string const Description;
+  bool Warned;
+} LookupTable[] = {};
+static_assert(sizeof(LookupTable) / sizeof(LookupTable[0]) ==
+                static_cast<size_t>(cmExperimental::Feature::Sentinel),
+              "Experimental feature lookup table mismatch");
+
+FeatureData& DataForFeature(cmExperimental::Feature f)
+{
+  assert(f != cmExperimental::Feature::Sentinel);
+  return LookupTable[static_cast<size_t>(f)];
+}
+}
+
+bool cmExperimental::HasSupportEnabled(cmMakefile const& mf, Feature f)
+{
+  bool enabled = false;
+  auto& data = DataForFeature(f);
+
+  auto value = mf.GetDefinition(data.Variable);
+  if (value == data.Uuid) {
+    enabled = true;
+  }
+
+  if (enabled && !data.Warned) {
+    mf.IssueMessage(MessageType::AUTHOR_WARNING, data.Description);
+    data.Warned = true;
+  }
+
+  return enabled;
+}