fileapi: Add protocol v1 infrastructure with support for shared query files

Add a file-based API that clients may use to get semantic information
about the buildsystem that CMake generates.  Clients will write query
files under a designated location in the build tree, and CMake will
write reply files for clients to read.

Start with support for shared stateless query files.  These allow
clients to share requests for major object versions and get all those
recognized by CMake.  Once any client has written a shared request to a
build tree it will persist.  Other clients will not need to overwrite
the request (since it is stateless) and should not remove it either.

For now we add only an undocumented object kind to use for testing the
query and reply infrastructure.  Object kinds providing real semantic
information will be added later.

Issue: #18398

1 files changed, 109 insertions, 0 deletions

diff --git a/Source/cmFileAPI.h b/Source/cmFileAPI.h
new file mode 100644
index 0000000..39b054d
--- /dev/null
+++ b/Source/cmFileAPI.h
@@ -0,0 +1,109 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#ifndef cmFileAPI_h
+#define cmFileAPI_h
+
+#include "cmConfigure.h" // IWYU pragma: keep
+
+#include "cm_jsoncpp_value.h"
+#include "cm_jsoncpp_writer.h"
+
+#include <map>
+#include <memory> // IWYU pragma: keep
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+class cmake;
+
+class cmFileAPI
+{
+public:
+  cmFileAPI(cmake* cm);
+
+  /** Read fileapi queries from disk.  */
+  void ReadQueries();
+
+  /** Write fileapi replies to disk.  */
+  void WriteReplies();
+
+  /** Get the "cmake" instance with which this was constructed.  */
+  cmake* GetCMakeInstance() const { return this->CMakeInstance; }
+
+private:
+  cmake* CMakeInstance;
+
+  /** The api/v1 directory location.  */
+  std::string APIv1;
+
+  /** The set of files we have just written to the reply directory.  */
+  std::unordered_set<std::string> ReplyFiles;
+
+  static std::vector<std::string> LoadDir(std::string const& dir);
+  void RemoveOldReplyFiles();
+
+  // Keep in sync with ObjectKindName.
+  enum class ObjectKind
+  {
+    InternalTest
+  };
+
+  /** Identify one object kind and major version.  */
+  struct Object
+  {
+    ObjectKind Kind;
+    unsigned long Version = 0;
+    friend bool operator<(Object const& l, Object const& r)
+    {
+      if (l.Kind != r.Kind) {
+        return l.Kind < r.Kind;
+      }
+      return l.Version < r.Version;
+    }
+  };
+
+  /** Represent content of a query directory.  */
+  struct Query
+  {
+    /** Known object kind-version pairs.  */
+    std::vector<Object> Known;
+    /** Unknown object kind names.  */
+    std::vector<std::string> Unknown;
+  };
+
+  /** Whether the top-level query directory exists at all.  */
+  bool QueryExists = false;
+
+  /** The content of the top-level query directory.  */
+  Query TopQuery;
+
+  /** Reply index object generated for object kind/version.
+      This populates the "objects" field of the reply index.  */
+  std::map<Object, Json::Value> ReplyIndexObjects;
+
+  std::unique_ptr<Json::StreamWriter> JsonWriter;
+
+  std::string WriteJsonFile(
+    Json::Value const& value, std::string const& prefix,
+    std::string (*computeSuffix)(std::string const&) = ComputeSuffixHash);
+  static std::string ComputeSuffixHash(std::string const&);
+  static std::string ComputeSuffixTime(std::string const&);
+
+  static bool ReadQuery(std::string const& query,
+                        std::vector<Object>& objects);
+
+  Json::Value BuildReplyIndex();
+  Json::Value BuildCMake();
+  Json::Value BuildReply(Query const& q);
+  static Json::Value BuildReplyError(std::string const& error);
+  Json::Value const& AddReplyIndexObject(Object const& o);
+
+  static const char* ObjectKindName(ObjectKind kind);
+  static std::string ObjectName(Object const& o);
+
+  Json::Value BuildObject(Object const& object);
+
+  Json::Value BuildInternalTest(Object const& object);
+};
+
+#endif