Merge pull request swiftlang#50 from ddunbar/libllbuild-get-signature

[libllbuild] Allow clients to supply custom command signatures.

Author: ddunbar

examples/c-api/buildsystem/main.c

@@ -52,6 +52,7 @@ static llb_buildsystem_command_t*
 fancy_tool_create_command(void *context, const llb_data_t* name) {
   llb_buildsystem_external_command_delegate_t delegate;
   delegate.context = NULL;
+  delegate.get_signature = NULL;
   delegate.execute_command = fancy_command_execute_command;
   return llb_buildsystem_external_command_create(name, delegate);
 }

products/libllbuild/BuildSystem-C-API.cpp

@@ -20,6 +20,7 @@
 #include "llbuild/BuildSystem/ExternalCommand.h"
 #include "llbuild/Core/BuildEngine.h"
 
+#include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/raw_ostream.h"
@@ -409,6 +410,24 @@ class CAPIExternalCommand : public ExternalCommand {
     // FIXME: Provide client control.
     llvm::raw_svector_ostream(result) << getName();
   }
+
+  virtual uint64_t getSignature() override {
+    // FIXME: Use a more appropriate hashing infrastructure.
+    using llvm::hash_combine;
+    llvm::hash_code code = ExternalCommand::getSignature();
+    if (cAPIDelegate.get_signature) {
+      llb_data_t data;
+      cAPIDelegate.get_signature(cAPIDelegate.context, (llb_buildsystem_command_t*)this,
+                                 &data);
+      code = hash_combine(code, StringRef((const char*)data.data, data.length));
+
+      // Release the client memory.
+      //
+      // FIXME: This is gross, come up with a general purpose solution.
+      free((char*)data.data);
+    }
+    return size_t(code);
+  }
 };
 
 }

products/libllbuild/public-api/llbuild/buildsystem.h

@@ -371,6 +371,19 @@ typedef struct llb_buildsystem_external_command_delegate_t_ {
   /// User context pointer.
   void* context;
 
+  /// Called to get a signature which represents the internal state of the
+  /// command which is not tracked by any other attribute visible to the build
+  /// system (for example, a declared input or output). This signature is
+  /// compared with previous executions of the command when determining whether
+  /// or not it needs to rerun.
+  ///
+  /// The contents *MUST* be returned in a new buffer allocated with \see
+  /// malloc().
+  //
+  // FIXME: We need to use a better data type than a uint64_t here.
+  void (*get_signature)(void* context, llb_buildsystem_command_t* command,
+                        llb_data_t* data_out);
+
   /// Called by the build system's execution queue after the command's inputs
   /// are available and the execution queue is ready to schedule the command.
   ///