cmake: Add `cmake -E capabilities` mode

Add `cmake -E capabilities` to report on generators, cmake version and
possibly other static capabilities of cmake.

Closes: #15462

1 files changed, 12 insertions, 0 deletions

diff --git a/Source/cmcmd.cxx b/Source/cmcmd.cxx
index 9d0337a..be023b1 100644
--- a/Source/cmcmd.cxx
+++ b/Source/cmcmd.cxx
@@ -60,6 +60,8 @@ void CMakeCommandUsage(const char* program)
   errorStream
     << "Usage: " << program << " -E <command> [arguments...]\n"
     << "Available commands: \n"
+    << "  capabilities              - Report capabilities built into cmake "
+       "in JSON format\n"
     << "  chdir dir cmd [args...]   - run command in a given directory\n"
     << "  compare_files file1 file2 - check if file1 is same as file2\n"
     << "  copy <file>... destination  - copy files to destination "
@@ -510,6 +512,16 @@ int cmcmd::ExecuteCMakeCommand(std::vector<std::string>& args)
       }
       return 0;
     }
+    // capabilities
+    else if (args[1] == "capabilities") {
+      if (args.size() > 2) {
+        std::cerr << "-E capabilities accepts no additional arguments\n";
+        return 1;
+      }
+      cmake cm;
+      std::cout << cm.ReportCapabilities();
+      return 0;
+    }
 
     // Sleep command
     else if (args[1] == "sleep" && args.size() > 2) {