1 files changed, 17 insertions, 0 deletions
diff --git a/src/libstore/file-hash.hh b/src/libstore/file-hash.hh
index 94122db07..9d2b78688 100644
--- a/src/libstore/file-hash.hh
+++ b/src/libstore/file-hash.hh
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <variant>
 #include "hash.hh"
 
 namespace nix {
@@ -23,6 +24,22 @@ struct FileSystemHash {
     std::string printMethodAlgo() const;
 };
 
+/*
+  We've accumulated several types of content-addressed paths over the years;
+  fixed-output derivations support multiple hash algorithms and serialisation
+  methods (flat file vs NAR). Thus, ‘ca’ has one of the following forms:
+
+  * ‘text:sha256:<sha256 hash of file contents>’: For paths
+    computed by makeTextPath() / addTextToStore().
+
+  * ‘fixed:<r?>:<ht>:<h>’: For paths computed by
+    makeFixedOutputPath() / addToStore().
+*/
+typedef std::variant<
+    Hash, // for paths computed by makeTextPath() / addTextToStore
+    FileSystemHash // for path computed by makeFixedOutputPath
+> ContentAddress;
+
 /* Compute the prefix to the hash algorithm which indicates how the files were
    ingested. */
 std::string makeFileIngestionPrefix(const FileIngestionMethod m);