libutil: Make HashResult a proper struct

This resolves an existing TODO and makes the
code slightly more readable.

src/libutil/file-content-address.cc

@@ -101,7 +101,7 @@ hashPath(const SourcePath & path, FileIngestionMethod method, HashAlgorithm ht,
     case FileIngestionMethod::Flat:
     case FileIngestionMethod::NixArchive: {
         auto res = hashPath(path, (FileSerialisationMethod) method, ht, filter);
-        return {res.first, {res.second}};
+        return {res.hash, res.numBytesDigested};
     }
     case FileIngestionMethod::Git:
         return {git::dumpHash(ht, path, filter).hash, std::nullopt};

src/libutil/git.cc

@@ -329,7 +329,7 @@ TreeEntry dumpHash(HashAlgorithm ha, const SourcePath & path, PathFilter & filte
     hook = [&](const SourcePath & path) -> TreeEntry {
         auto hashSink = HashSink(ha);
         auto mode = dump(path, hashSink, hook, filter);
-        auto hash = hashSink.finish().first;
+        auto hash = hashSink.finish().hash;
         return {
             .mode = mode,
             .hash = hash,

src/libutil/hash.cc

@@ -338,7 +338,7 @@ Hash hashFile(HashAlgorithm ha, const Path & path)
 {
     HashSink sink(ha);
     readFile(path, sink);
-    return sink.finish().first;
+    return sink.finish().hash;
 }
 
 HashSink::HashSink(HashAlgorithm ha)

src/libutil/include/nix/util/hash.hh

@@ -153,10 +153,12 @@ Hash hashFile(HashAlgorithm ha, const Path & path);
 
 /**
  * The final hash and the number of bytes digested.
- *
- * @todo Convert to proper struct
  */
-typedef std::pair<Hash, uint64_t> HashResult;
+struct HashResult
+{
+    Hash hash;
+    uint64_t numBytesDigested;
+};
 
 /**
  * Compress a hash to the specified number of bytes by cyclically

src/libutil/references.cc

@@ -120,7 +120,7 @@ HashResult HashModuloSink::finish()
         hashSink(fmt("|%d", pos));
 
     auto h = hashSink.finish();
-    return {h.first, rewritingSink.pos};
+    return {.hash = h.hash, .numBytesDigested = rewritingSink.pos};
 }
 
 } // namespace nix

src/libutil/source-accessor.cc

@@ -65,7 +65,7 @@ Hash SourceAccessor::hashPath(const CanonPath & path, PathFilter & filter, HashA
 {
     HashSink sink(ha);
     dumpPath(path, sink, filter);
-    return sink.finish().first;
+    return sink.finish().hash;
 }
 
 SourceAccessor::Stat SourceAccessor::lstat(const CanonPath & path)