From 50aae0a14c5bbbde5785ead8f46b28333e6248ae Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 1 Nov 2023 15:39:40 +0100
Subject: [PATCH] FSAccessor: Make the fileSize and narOffset fields optional

The narOffset field only applies to NAR accessors. The fileSize field
may be too expensive to compute for certain accessors (e.g. libgit).
---
 src/libstore/fs-accessor.hh  |  4 ++--
 src/libstore/nar-accessor.cc | 11 ++++++-----
 src/nix/ls.cc                |  2 +-
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/src/libstore/fs-accessor.hh b/src/libstore/fs-accessor.hh
index f04a92206..f6c002a2d 100644
--- a/src/libstore/fs-accessor.hh
+++ b/src/libstore/fs-accessor.hh
@@ -23,7 +23,7 @@ public:
         /**
          * For regular files only: the size of the file.
          */
-        uint64_t fileSize = 0;
+        std::optional<uint64_t> fileSize;
         /**
          * For regular files only: whether this is an executable.
          */
@@ -32,7 +32,7 @@ public:
          * For regular files only: the position of the contents of this
          * file in the NAR.
          */
-        uint64_t narOffset = 0;
+        std::optional<uint64_t> narOffset;
     };
 
     virtual ~FSAccessor() { }
diff --git a/src/libstore/nar-accessor.cc b/src/libstore/nar-accessor.cc
index fe857a60e..f1be5606e 100644
--- a/src/libstore/nar-accessor.cc
+++ b/src/libstore/nar-accessor.cc
@@ -210,10 +210,10 @@ struct NarAccessor : public FSAccessor
         if (i.stat.type != Type::tRegular)
             throw Error("path '%1%' inside NAR file is not a regular file", path);
 
-        if (getNarBytes) return getNarBytes(i.stat.narOffset, i.stat.fileSize);
+        if (getNarBytes) return getNarBytes(*i.stat.narOffset, *i.stat.fileSize);
 
         assert(nar);
-        return std::string(*nar, i.stat.narOffset, i.stat.fileSize);
+        return std::string(*nar, *i.stat.narOffset, *i.stat.fileSize);
     }
 
     std::string readLink(const Path & path) override
@@ -253,11 +253,12 @@ json listNar(ref<FSAccessor> accessor, const Path & path, bool recurse)
     switch (st->type) {
     case SourceAccessor::Type::tRegular:
         obj["type"] = "regular";
-        obj["size"] = st->fileSize;
+        if (st->fileSize)
+            obj["size"] = *st->fileSize;
         if (st->isExecutable)
             obj["executable"] = true;
-        if (st->narOffset)
-            obj["narOffset"] = st->narOffset;
+        if (st->narOffset && *st->narOffset)
+            obj["narOffset"] = *st->narOffset;
         break;
     case SourceAccessor::Type::tDirectory:
         obj["type"] = "directory";
diff --git a/src/nix/ls.cc b/src/nix/ls.cc
index 0ca08cea8..da978f379 100644
--- a/src/nix/ls.cc
+++ b/src/nix/ls.cc
@@ -52,7 +52,7 @@ struct MixLs : virtual Args, MixJSON
                         (st->isExecutable ? "-r-xr-xr-x" : "-r--r--r--") :
                     st->type == FSAccessor::Type::tSymlink ? "lrwxrwxrwx" :
                     "dr-xr-xr-x";
-                auto line = fmt("%s %20d %s", tp, st->fileSize, relPath);
+                auto line = fmt("%s %20d %s", tp, st->fileSize.value_or(0), relPath);
                 if (st->type == FSAccessor::Type::tSymlink)
                     line += " -> " + accessor->readLink(curPath);
                 logger->cout(line);