Merge remote-tracking branch 'upstream/master' into multi-output-hashDerivationModulo

13 files changed, 180 insertions, 97 deletions

diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index f8eff508c..9f52ddafa 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -388,8 +388,6 @@ void BinaryCacheStore::addSignatures(const StorePath & storePath, const StringSe
 
     narInfo->sigs.insert(sigs.begin(), sigs.end());
 
-    auto narInfoFile = narInfoFileFor(narInfo->path);
-
     writeNarInfo(narInfo);
 }
 
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 53a0958aa..82a2ab831 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -86,7 +86,7 @@ struct HookInstance;
 
 
 /* A pointer to a goal. */
-class Goal;
+struct Goal;
 class DerivationGoal;
 typedef std::shared_ptr<Goal> GoalPtr;
 typedef std::weak_ptr<Goal> WeakGoalPtr;
@@ -1195,6 +1195,12 @@ void DerivationGoal::haveDerivation()
 
     parsedDrv = std::make_unique<ParsedDerivation>(drvPath, *drv);
 
+    if (parsedDrv->contentAddressed()) {
+        settings.requireExperimentalFeature("ca-derivations");
+        throw Error("ca-derivations isn't implemented yet");
+    }
+
+
     /* We are first going to try to create the invalid output paths
        through substitutes.  If that doesn't work, we'll build
        them. */
@@ -3712,10 +3718,7 @@ void DerivationGoal::registerOutputs()
 
         if (fixedOutput) {
 
-            FileIngestionMethod outputHashMode; Hash h;
-            i.second.parseHashInfo(outputHashMode, h);
-
-            if (outputHashMode == FileIngestionMethod::Flat) {
+            if (i.second.hash->method == FileIngestionMethod::Flat) {
                 /* The output path should be a regular file without execute permission. */
                 if (!S_ISREG(st.st_mode) || (st.st_mode & S_IXUSR) != 0)
                     throw BuildError(
@@ -3726,20 +3729,22 @@ void DerivationGoal::registerOutputs()
 
             /* Check the hash. In hash mode, move the path produced by
                the derivation to its content-addressed location. */
-            Hash h2 = outputHashMode == FileIngestionMethod::Recursive
-                ? hashPath(h.type, actualPath).first
-                : hashFile(h.type, actualPath);
+            Hash h2 = i.second.hash->method == FileIngestionMethod::Recursive
+                ? hashPath(*i.second.hash->hash.type, actualPath).first
+                : hashFile(*i.second.hash->hash.type, actualPath);
 
-            auto dest = worker.store.makeFixedOutputPath(outputHashMode, h2, i.second.path.name());
+            auto dest = worker.store.makeFixedOutputPath(i.second.hash->method, h2, i.second.path.name());
 
-            if (h != h2) {
+            if (i.second.hash->hash != h2) {
 
                 /* Throw an error after registering the path as
                    valid. */
                 worker.hashMismatch = true;
                 delayedException = std::make_exception_ptr(
                     BuildError("hash mismatch in fixed-output derivation '%s':\n  wanted: %s\n  got:    %s",
-                        worker.store.printStorePath(dest), h.to_string(SRI, true), h2.to_string(SRI, true)));
+                        worker.store.printStorePath(dest),
+                        i.second.hash->hash.to_string(SRI, true),
+                        h2.to_string(SRI, true)));
 
                 Path actualDest = worker.store.Store::toRealPath(dest);
 
@@ -3759,7 +3764,7 @@ void DerivationGoal::registerOutputs()
             else
                 assert(worker.store.parseStorePath(path) == dest);
 
-            ca = makeFixedOutputCA(outputHashMode, h2);
+            ca = makeFixedOutputCA(i.second.hash->method, h2);
         }
 
         /* Get rid of all weird permissions.  This also checks that
@@ -4992,7 +4997,7 @@ bool Worker::pathContentsGood(const StorePath & path)
     if (!pathExists(store.printStorePath(path)))
         res = false;
     else {
-        HashResult current = hashPath(info->narHash.type, store.printStorePath(path));
+        HashResult current = hashPath(*info->narHash.type, store.printStorePath(path));
         Hash nullHash(htSHA256);
         res = info->narHash == nullHash || info->narHash == current.first;
     }
diff --git a/src/libstore/builtins/fetchurl.cc b/src/libstore/builtins/fetchurl.cc
index 2048f8f87..1cfe4a46a 100644
--- a/src/libstore/builtins/fetchurl.cc
+++ b/src/libstore/builtins/fetchurl.cc
@@ -63,9 +63,9 @@ void builtinFetchurl(const BasicDerivation & drv, const std::string & netrcData)
         for (auto hashedMirror : settings.hashedMirrors.get())
             try {
                 if (!hasSuffix(hashedMirror, "/")) hashedMirror += '/';
-                auto ht = parseHashType(getAttr("outputHashAlgo"));
+                auto ht = parseHashTypeOpt(getAttr("outputHashAlgo"));
                 auto h = Hash(getAttr("outputHash"), ht);
-                fetch(hashedMirror + printHashType(h.type) + "/" + h.to_string(Base16, false));
+                fetch(hashedMirror + printHashType(*h.type) + "/" + h.to_string(Base16, false));
                 return;
             } catch (Error & e) {
                 debug(e.what());
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 065702c37..1f64086d7 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -8,22 +8,8 @@
 
 namespace nix {
 
-
-void DerivationOutput::parseHashInfo(FileIngestionMethod & recursive, Hash & hash) const
-{
-    recursive = FileIngestionMethod::Flat;
-    string algo = hashAlgo;
-
-    if (string(algo, 0, 2) == "r:") {
-        recursive = FileIngestionMethod::Recursive;
-        algo = string(algo, 2);
-    }
-
-    HashType hashType = parseHashType(algo);
-    if (hashType == htUnknown)
-        throw Error("unknown hash algorithm '%s'", algo);
-
-    hash = Hash(this->hash, hashType);
+std::string DerivationOutputHash::printMethodAlgo() const {
+    return makeFileIngestionPrefix(method) + printHashType(*hash.type);
 }
 
 
@@ -120,6 +106,34 @@ static StringSet parseStrings(std::istream & str, bool arePaths)
 }
 
 
+static DerivationOutput parseDerivationOutput(const Store & store, istringstream_nocopy & str)
+{
+    expect(str, ","); auto path = store.parseStorePath(parsePath(str));
+    expect(str, ","); auto hashAlgo = parseString(str);
+    expect(str, ","); const auto hash = parseString(str);
+    expect(str, ")");
+
+    std::optional<DerivationOutputHash> fsh;
+    if (hashAlgo != "") {
+        auto method = FileIngestionMethod::Flat;
+        if (string(hashAlgo, 0, 2) == "r:") {
+            method = FileIngestionMethod::Recursive;
+            hashAlgo = string(hashAlgo, 2);
+        }
+        const HashType hashType = parseHashType(hashAlgo);
+        fsh = DerivationOutputHash {
+            .method = std::move(method),
+            .hash = Hash(hash, hashType),
+        };
+    }
+
+    return DerivationOutput {
+        .path = std::move(path),
+        .hash = std::move(fsh),
+    };
+}
+
+
 static Derivation parseDerivation(const Store & store, const string & s)
 {
     Derivation drv;
@@ -129,15 +143,8 @@ static Derivation parseDerivation(const Store & store, const string & s)
     /* Parse the list of outputs. */
     while (!endOfList(str)) {
         expect(str, "("); std::string id = parseString(str);
-        expect(str, ","); auto path = store.parseStorePath(parsePath(str));
-        expect(str, ","); auto hashAlgo = parseString(str);
-        expect(str, ","); auto hash = parseString(str);
-        expect(str, ")");
-        drv.outputs.emplace(id, DerivationOutput {
-            .path = std::move(path),
-            .hashAlgo = std::move(hashAlgo),
-            .hash = std::move(hash)
-        });
+        auto output = parseDerivationOutput(store, str);
+        drv.outputs.emplace(std::move(id), std::move(output));
     }
 
     /* Parse the list of input derivations. */
@@ -263,8 +270,9 @@ string Derivation::unparse(const Store & store, bool maskOutputs,
         if (first) first = false; else s += ',';
         s += '('; printUnquotedString(s, i.first);
         s += ','; printUnquotedString(s, maskOutputs ? "" : store.printStorePath(i.second.path));
-        s += ','; printUnquotedString(s, i.second.hashAlgo);
-        s += ','; printUnquotedString(s, i.second.hash);
+        s += ','; printUnquotedString(s, i.second.hash ? i.second.hash->printMethodAlgo() : "");
+        s += ','; printUnquotedString(s,
+            i.second.hash ? i.second.hash->hash.to_string(Base16, false) : "");
         s += ')';
     }
 
@@ -320,7 +328,7 @@ bool BasicDerivation::isFixedOutput() const
 {
     return outputs.size() == 1 &&
         outputs.begin()->first == "out" &&
-        outputs.begin()->second.hash != "";
+        outputs.begin()->second.hash;
 }
 
 
@@ -332,7 +340,7 @@ DrvHashes drvHashes;
 /* Look up the derivation by value and memoize the
    `hashDerivationModulo` call.
  */
-static DrvHashModulo & pathDerivationModulo(Store & store, const StorePath & drvPath)
+static const DrvHashModulo & pathDerivationModulo(Store & store, const StorePath & drvPath)
 {
     auto h = drvHashes.find(drvPath);
     if (h == drvHashes.end()) {
@@ -348,6 +356,10 @@ static DrvHashModulo & pathDerivationModulo(Store & store, const StorePath & drv
     return h->second;
 }
 
+// FIXME: Boilerplatflate for `std::visit`, put this somewhere?
+template<class... Ts> struct overloaded : Ts... { using Ts::operator()...; };
+template<class... Ts> overloaded(Ts...) -> overloaded<Ts...>;
+
 /* See the header for interface details. These are the implementation details.
 
    For fixed-output derivations, each hash in the map is not the
@@ -372,8 +384,8 @@ DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool m
         std::map<std::string, Hash> outputHashes;
         for (const auto & i : drv.outputs) {
             const Hash h = hashString(htSHA256, "fixed:out:"
-                + i.second.hashAlgo + ":"
-                + i.second.hash + ":"
+                + i.second.hash->printMethodAlgo() + ":"
+                + i.second.hash->hash.to_string(Base16, false) + ":"
                 + store.printStorePath(i.second.path));
             outputHashes.insert_or_assign(std::string(i.first), std::move(h));
         }
@@ -384,21 +396,24 @@ DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool m
        calls to this function. */
     std::map<std::string, StringSet> inputs2;
     for (auto & i : drv.inputDrvs) {
-        const auto res = pathDerivationModulo(store, i.first);
-        if (const Hash *pval = std::get_if<0>(&res)) {
-            // regular non-CA derivation, replace derivation
-            inputs2.insert_or_assign(pval->to_string(Base16, false), i.second);
-        } else if (const std::map<std::string, Hash> *pval = std::get_if<1>(&res)) {
+        const auto & res = pathDerivationModulo(store, i.first);
+        std::visit(overloaded {
+            // Regular non-CA derivation, replace derivation
+            [&](Hash drvHash) {
+                inputs2.insert_or_assign(drvHash.to_string(Base16, false), i.second);
+            },
             // CA derivation's output hashes
-            std::set justOut = { std::string("out") };
-            for (auto & output : i.second) {
-                /* Put each one in with a single "out" output.. */
-                const auto h = pval->at(output);
-                inputs2.insert_or_assign(
-                    h.to_string(Base16, false),
-                    justOut);
-            }
-        }
+            [&](CaOutputHashes outputHashes) {
+                std::set justOut = { std::string("out") };
+                for (auto & output : i.second) {
+                    /* Put each one in with a single "out" output.. */
+                    const auto h = outputHashes.at(output);
+                    inputs2.insert_or_assign(
+                        h.to_string(Base16, false),
+                        justOut);
+                }
+            },
+        }, res);
     }
 
     return hashString(htSHA256, drv.unparse(store, maskOutputs, &inputs2));
@@ -427,6 +442,31 @@ StorePathSet BasicDerivation::outputPaths() const
     return paths;
 }
 
+static DerivationOutput readDerivationOutput(Source & in, const Store & store)
+{
+    auto path = store.parseStorePath(readString(in));
+    auto hashAlgo = readString(in);
+    const auto hash = readString(in);
+
+    std::optional<DerivationOutputHash> fsh;
+    if (hashAlgo != "") {
+        auto method = FileIngestionMethod::Flat;
+        if (string(hashAlgo, 0, 2) == "r:") {
+            method = FileIngestionMethod::Recursive;
+            hashAlgo = string(hashAlgo, 2);
+        }
+        const HashType hashType = parseHashType(hashAlgo);
+        fsh = DerivationOutputHash {
+            .method = std::move(method),
+            .hash = Hash(hash, hashType),
+        };
+    }
+
+    return DerivationOutput {
+        .path = std::move(path),
+        .hash = std::move(fsh),
+    };
+}
 
 StringSet BasicDerivation::outputNames() const
 {
@@ -443,14 +483,8 @@ Source & readDerivation(Source & in, const Store & store, BasicDerivation & drv)
     auto nr = readNum<size_t>(in);
     for (size_t n = 0; n < nr; n++) {
         auto name = readString(in);
-        auto path = store.parseStorePath(readString(in));
-        auto hashAlgo = readString(in);
-        auto hash = readString(in);
-        drv.outputs.emplace(name, DerivationOutput {
-            .path = std::move(path),
-            .hashAlgo = std::move(hashAlgo),
-            .hash = std::move(hash)
-        });
+        auto output = readDerivationOutput(in, store);
+        drv.outputs.emplace(std::move(name), std::move(output));
     }
 
     drv.inputSrcs = readStorePaths<StorePathSet>(store, in);
@@ -472,7 +506,10 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
 {
     out << drv.outputs.size();
     for (auto & i : drv.outputs)
-        out << i.first << store.printStorePath(i.second.path) << i.second.hashAlgo << i.second.hash;
+        out << i.first
+            << store.printStorePath(i.second.path)
+            << i.second.hash->printMethodAlgo()
+            << i.second.hash->hash.to_string(Base16, false);
     writeStorePaths(store, out, drv.inputSrcs);
     out << drv.platform << drv.builder << drv.args;
     out << drv.env.size();
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index 97271ac09..9b749598f 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -13,11 +13,17 @@ namespace nix {
 
 /* Abstract syntax of derivations. */
 
+/// Pair of a hash, and how the file system was ingested
+struct DerivationOutputHash {
+    FileIngestionMethod method;
+    Hash hash;
+    std::string printMethodAlgo() const;
+};
+
 struct DerivationOutput
 {
     StorePath path;
-    std::string hashAlgo; /* hash used for expected hash computation */
-    std::string hash; /* expected hash, may be null */
+    std::optional<DerivationOutputHash> hash; /* hash used for expected hash computation */
     void parseHashInfo(FileIngestionMethod & recursive, Hash & hash) const;
 };
 
@@ -82,9 +88,13 @@ Derivation readDerivation(const Store & store, const Path & drvPath);
 // FIXME: remove
 bool isDerivation(const string & fileName);
 
+// known CA drv's output hashes, current just for fixed-output derivations
+// whose output hashes are always known since they are fixed up-front.
+typedef std::map<std::string, Hash> CaOutputHashes;
+
 typedef std::variant<
     Hash, // regular DRV normalized hash
-    std::map<std::string, Hash> // known CA drv's output hashes
+    CaOutputHashes
 > DrvHashModulo;
 
 /* Returns hashes with the details of fixed-output subderivations
diff --git a/src/libstore/export-import.cc b/src/libstore/export-import.cc
index cb9da027d..57b7e9590 100644
--- a/src/libstore/export-import.cc
+++ b/src/libstore/export-import.cc
@@ -55,7 +55,7 @@ void Store::exportPath(const StorePath & path, Sink & sink)
        filesystem corruption from spreading to other machines.
        Don't complain if the stored hash is zero (unknown). */
     Hash hash = hashAndWriteSink.currentHash();
-    if (hash != info->narHash && info->narHash != Hash(info->narHash.type))
+    if (hash != info->narHash && info->narHash != Hash(*info->narHash.type))
         throw Error("hash of path '%s' has changed from '%s' to '%s'!",
             printStorePath(path), info->narHash.to_string(Base32, true), hash.to_string(Base32, true));
 
diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index c954ace7f..531b85af8 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -72,6 +72,7 @@ struct curlFileTransfer : public FileTransfer
 
         curl_off_t writtenToSink = 0;
 
+        inline static const std::set<long> successfulStatuses {200, 201, 204, 206, 304, 0 /* other protocol */};
         /* Get the HTTP status code, or 0 for other protocols. */
         long getHTTPStatus()
         {
@@ -98,7 +99,7 @@ struct curlFileTransfer : public FileTransfer
 
                     /* Only write data to the sink if this is a
                        successful response. */
-                    if (httpStatus == 0 || httpStatus == 200 || httpStatus == 201 || httpStatus == 206) {
+                    if (successfulStatuses.count(httpStatus)) {
                         writtenToSink += len;
                         this->request.dataCallback((char *) data, len);
                     }
@@ -352,8 +353,7 @@ struct curlFileTransfer : public FileTransfer
             if (writeException)
                 failEx(writeException);
 
-            else if (code == CURLE_OK &&
-                (httpStatus == 200 || httpStatus == 201 || httpStatus == 204 || httpStatus == 206 || httpStatus == 304 || httpStatus == 0 /* other protocol */))
+            else if (code == CURLE_OK && successfulStatuses.count(httpStatus))
             {
                 result.cached = httpStatus == 304;
                 act.progress(result.bodySize, result.bodySize);
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 460be97a1..6953d17de 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -561,10 +561,12 @@ void LocalStore::checkDerivationOutputs(const StorePath & drvPath, const Derivat
         if (out == drv.outputs.end())
             throw Error("derivation '%s' does not have an output named 'out'", printStorePath(drvPath));
 
-        FileIngestionMethod method; Hash h;
-        out->second.parseHashInfo(method, h);
-
-        check(makeFixedOutputPath(method, h, drvName), out->second.path, "out");
+        check(
+            makeFixedOutputPath(
+                out->second.hash->method,
+                out->second.hash->hash,
+                drvName),
+            out->second.path, "out");
     }
 
     else {
@@ -1255,9 +1257,9 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
 
                 std::unique_ptr<AbstractHashSink> hashSink;
                 if (info->ca == "" || !info->references.count(info->path))
-                    hashSink = std::make_unique<HashSink>(info->narHash.type);
+                    hashSink = std::make_unique<HashSink>(*info->narHash.type);
                 else
-                    hashSink = std::make_unique<HashModuloSink>(info->narHash.type, std::string(info->path.hashPart()));
+                    hashSink = std::make_unique<HashModuloSink>(*info->narHash.type, std::string(info->path.hashPart()));
 
                 dumpPath(Store::toRealPath(i), *hashSink);
                 auto current = hashSink->finish();
diff --git a/src/libstore/parsed-derivations.cc b/src/libstore/parsed-derivations.cc
index 24f848e46..c7797b730 100644
--- a/src/libstore/parsed-derivations.cc
+++ b/src/libstore/parsed-derivations.cc
@@ -117,4 +117,9 @@ bool ParsedDerivation::substitutesAllowed() const
     return getBoolAttr("allowSubstitutes", true);
 }
 
+bool ParsedDerivation::contentAddressed() const
+{
+    return getBoolAttr("__contentAddressed", false);
+}
+
 }
diff --git a/src/libstore/parsed-derivations.hh b/src/libstore/parsed-derivations.hh
index 7621342d7..d24d1eb4f 100644
--- a/src/libstore/parsed-derivations.hh
+++ b/src/libstore/parsed-derivations.hh
@@ -34,6 +34,8 @@ public:
     bool willBuildLocally() const;
 
     bool substitutesAllowed() const;
+
+    bool contentAddressed() const;
 };
 
 }
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index fc5ab5865..f5f2ab7fd 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -228,7 +228,7 @@ struct ConnectionHandle
 
     ~ConnectionHandle()
     {
-        if (!daemonException && std::uncaught_exception()) {
+        if (!daemonException && std::uncaught_exceptions()) {
             handle.markBad();
             debug("closing daemon connection because of an exception");
         }
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index aae227bae..982fc22b6 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -61,7 +61,7 @@ StorePathWithOutputs Store::followLinksToStorePathWithOutputs(std::string_view p
 
 /* Store paths have the following form:
 
-   <store>/<h>-<name>
+   <realized-path> = <store>/<h>-<name>
 
    where
 
@@ -85,11 +85,14 @@ StorePathWithOutputs Store::followLinksToStorePathWithOutputs(std::string_view p
    <type> = one of:
      "text:<r1>:<r2>:...<rN>"
        for plain text files written to the store using
-       addTextToStore(); <r1> ... <rN> are the references of the
-       path.
-     "source"
+       addTextToStore(); <r1> ... <rN> are the store paths referenced
+       by this path, in the form described by <realized-path>
+     "source:<r1>:<r2>:...:<rN>:self"
        for paths copied to the store using addToStore() when recursive
-       = true and hashAlgo = "sha256"
+       = true and hashAlgo = "sha256". Just like in the text case, we
+       can have the store paths referenced by the path.
+       Additionally, we can have an optional :self label to denote self
+       reference.
      "output:<id>"
        for either the outputs created by derivations, OR paths copied
        to the store using addToStore() with recursive != true or
@@ -117,6 +120,12 @@ StorePathWithOutputs Store::followLinksToStorePathWithOutputs(std::string_view p
              the contents of the path (or expected contents of the
              path for fixed-output derivations)
 
+   Note that since an output derivation has always type output, while
+   something added by addToStore can have type output or source depending
+   on the hash, this means that the same input can be hashed differently
+   if added to the store via addToStore or via a derivation, in the sha256
+   recursive case.
+
    It would have been nicer to handle fixed-output derivations under
    "source", e.g. have something like "source:<rec><algo>", but we're
    stuck with this for now...
@@ -164,20 +173,20 @@ static std::string makeType(
 
 
 StorePath Store::makeFixedOutputPath(
-    FileIngestionMethod recursive,
+    FileIngestionMethod method,
     const Hash & hash,
     std::string_view name,
     const StorePathSet & references,
     bool hasSelfReference) const
 {
-    if (hash.type == htSHA256 && recursive == FileIngestionMethod::Recursive) {
+    if (hash.type == htSHA256 && method == FileIngestionMethod::Recursive) {
         return makeStorePath(makeType(*this, "source", references, hasSelfReference), hash, name);
     } else {
         assert(references.empty());
         return makeStorePath("output:out",
             hashString(htSHA256,
                 "fixed:out:"
-                + (recursive == FileIngestionMethod::Recursive ? (string) "r:" : "")
+                + makeFileIngestionPrefix(method)
                 + hash.to_string(Base16, true) + ":"),
             name);
     }
@@ -813,10 +822,21 @@ Strings ValidPathInfo::shortRefs() const
 }
 
 
-std::string makeFixedOutputCA(FileIngestionMethod recursive, const Hash & hash)
+std::string makeFileIngestionPrefix(const FileIngestionMethod m) {
+    switch (m) {
+    case FileIngestionMethod::Flat:
+        return "";
+    case FileIngestionMethod::Recursive:
+        return "r:";
+    default:
+        throw Error("impossible, caught both cases");
+    }
+}
+
+std::string makeFixedOutputCA(FileIngestionMethod method, const Hash & hash)
 {
     return "fixed:"
-        + (recursive == FileIngestionMethod::Recursive ? (std::string) "r:" : "")
+        + makeFileIngestionPrefix(method)
         + hash.to_string(Base32, true);
 }
 
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 6f4dd959c..a05048290 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -189,9 +189,10 @@ struct ValidPathInfo
 
     Strings shortRefs() const;
 
-    ValidPathInfo(const StorePath & path) : path(path) { }
+    ValidPathInfo(const ValidPathInfo & other) = default;
 
-    ValidPathInfo(StorePath && path) : path(std::move(path)) { }
+    ValidPathInfo(StorePath && path) : path(std::move(path)) { };
+    ValidPathInfo(const StorePath & path) : path(path) { };
 
     virtual ~ValidPathInfo() { }
 };
@@ -838,6 +839,9 @@ std::optional<ValidPathInfo> decodeValidPathInfo(
     std::istream & str,
     bool hashGiven = false);
 
+/* Compute the prefix to the hash algorithm which indicates how the files were
+   ingested. */
+std::string makeFileIngestionPrefix(const FileIngestionMethod m);
 
 /* Compute the content-addressability assertion (ValidPathInfo::ca)
    for paths created by makeFixedOutputPath() / addToStore(). */