cmake: Teach -E capabilities to report supported fileapi requests

Fixes: #19339

Help/manual/cmake-file-api.7.rst

@@ -379,6 +379,8 @@ finds the file missing, that means a concurrent CMake has generated
 a new reply.  The client may simply start again by reading the new
 reply index file.
 
+.. _`file-api object kinds`:
+
 Object Kinds
 ============
 

Help/manual/cmake.1.rst

@@ -423,6 +423,22 @@ Available commands are:
       A list of strings with all the extra generators compatible with
       the generator.
 
+  ``fileApi``
+    Optional member that is present when the :manual:`cmake-file-api(7)`
+    is available.  The value is a JSON object with one member:
+
+    ``requests``
+      A JSON array containing zero or more supported file-api requests.
+      Each request is a JSON object with members:
+
+      ``kind``
+        Specifies one of the supported :ref:`file-api object kinds`.
+
+      ``version``
+        A JSON array whose elements are each a JSON object containing
+        ``major`` and ``minor`` members specifying non-negative integer
+        version components.
+
   ``serverMode``
     ``true`` if cmake supports server-mode and ``false`` otherwise.
 

Source/cmFileAPI.cxx

@@ -801,3 +801,35 @@ Json::Value cmFileAPI::BuildInternalTest(Object const& object)
   }
   return test;
 }
+
+Json::Value cmFileAPI::ReportCapabilities()
+{
+  Json::Value capabilities = Json::objectValue;
+  Json::Value& requests = capabilities["requests"] = Json::arrayValue;
+
+  {
+    Json::Value request = Json::objectValue;
+    request["kind"] = ObjectKindName(ObjectKind::CodeModel);
+    Json::Value& versions = request["version"] = Json::arrayValue;
+    versions.append(BuildVersion(2, CodeModelV2Minor));
+    requests.append(std::move(request));
+  }
+
+  {
+    Json::Value request = Json::objectValue;
+    request["kind"] = ObjectKindName(ObjectKind::Cache);
+    Json::Value& versions = request["version"] = Json::arrayValue;
+    versions.append(BuildVersion(2, CacheV2Minor));
+    requests.append(std::move(request));
+  }
+
+  {
+    Json::Value request = Json::objectValue;
+    request["kind"] = ObjectKindName(ObjectKind::CMakeFiles);
+    Json::Value& versions = request["version"] = Json::arrayValue;
+    versions.append(BuildVersion(1, CMakeFilesV1Minor));
+    requests.append(std::move(request));
+  }
+
+  return capabilities;
+}

Source/cmFileAPI.h

@@ -36,6 +36,9 @@ public:
       and holding the original object.  Other JSON types are unchanged.  */
   Json::Value MaybeJsonFile(Json::Value in, std::string const& prefix);
 
+  /** Report file-api capabilities for cmake -E capabilities.  */
+  static Json::Value ReportCapabilities();
+
 private:
   cmake* CMakeInstance;
 

Source/cmake.cxx

@@ -284,6 +284,7 @@ Json::Value cmake::ReportCapabilitiesJson() const
     generators.append(i.second);
   }
   obj["generators"] = generators;
+  obj["fileApi"] = cmFileAPI::ReportCapabilities();
   obj["serverMode"] = true;
 
   return obj;

Tests/RunCMake/CommandLine/E_capabilities-stdout.txt

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