cmake -E capabilities: Tell whether TLS is enabled

Fixes: #20507

Help/manual/cmake.1.rst

@@ -773,6 +773,11 @@ Available commands are:
     ``true`` if cmake supports server-mode and ``false`` otherwise.
     Always false since CMake 3.20.
 
+  ``tls``
+    .. versionadded:: 3.25
+
+    ``true`` if TLS support is enabled and ``false`` otherwise.
+
 .. option:: cat [--] <files>...
 
   .. versionadded:: 3.18

Help/release/dev/E-capabilities-tls.rst

@@ -0,0 +1,5 @@
+E-capabilities-tls
+------------------
+
+* The :manual:`cmake -E capabilities <cmake(1)>` command gained a new ``tls``
+  field that tells whether or not TLS is enabled.

Source/cmake.cxx

@@ -63,6 +63,7 @@
 #if !defined(CMAKE_BOOTSTRAP)
 #  include <unordered_map>
 
+#  include <cm3p/curl/curl.h>
 #  include <cm3p/json/writer.h>
 
 #  include "cmFileAPI.h"
@@ -252,6 +253,8 @@ Json::Value cmake::ReportCapabilitiesJson() const
   std::vector<cmake::GeneratorInfo> generatorInfoList;
   this->GetRegisteredGenerators(generatorInfoList);
 
+  auto* curlVersion = curl_version_info(CURLVERSION_FIRST);
+
   JsonValueMapType generatorMap;
   for (cmake::GeneratorInfo const& gi : generatorInfoList) {
     if (gi.isAlias) { // skip aliases, they are there for compatibility reasons
@@ -286,6 +289,7 @@ Json::Value cmake::ReportCapabilitiesJson() const
   obj["generators"] = generators;
   obj["fileApi"] = cmFileAPI::ReportCapabilities();
   obj["serverMode"] = false;
+  obj["tls"] = static_cast<bool>(curlVersion->features & CURL_VERSION_SSL);
 
   return obj;
 }

Tests/RunCMake/CommandLine/E_capabilities-stdout.txt

@@ -1 +1 @@
-^{"fileApi":{"requests":\[{"kind":"codemodel","version":\[{"major":2,"minor":4}]},{"kind":"cache","version":\[{"major":2,"minor":0}]},{"kind":"cmakeFiles","version":\[{"major":1,"minor":0}]},{"kind":"toolchains","version":\[{"major":1,"minor":0}]}]},"generators":\[.*\],"serverMode":false,"version":{.*}}$
+^{"fileApi":{"requests":\[{"kind":"codemodel","version":\[{"major":2,"minor":4}]},{"kind":"cache","version":\[{"major":2,"minor":0}]},{"kind":"cmakeFiles","version":\[{"major":1,"minor":0}]},{"kind":"toolchains","version":\[{"major":1,"minor":0}]}]},"generators":\[.*\],"serverMode":false,"tls":(true|false),"version":{.*}}$