Add support for tarball flake inputs

For example,

  $ nix flake info https://github.com/edolstra/dwarffs/archive/master.tar.gz

Fixes #2929.

src/libstore/fetchers/fetchers.cc

@@ -39,6 +39,10 @@ std::pair<Tree, std::shared_ptr<const Input>> Input::fetchTree(ref<Store> store)
     if (input->narHash)
         assert(input->narHash == tree.narHash);
 
+    if (narHash && narHash != input->narHash)
+        throw Error("NAR hash mismatch in input '%s', expected '%s', got '%s'",
+            to_string(), narHash->to_string(SRI), input->narHash->to_string(SRI));
+
     return {std::move(tree), input};
 }
 

src/libstore/fetchers/fetchers.hh

@@ -25,7 +25,7 @@ struct Tree
 struct Input : std::enable_shared_from_this<Input>
 {
     std::string type;
-    std::optional<Hash> narHash;
+    std::optional<Hash> narHash; // FIXME: implement
 
     virtual ~Input() { }
 

src/libstore/fetchers/tarball.cc

@@ -0,0 +1,91 @@
+#include "fetchers.hh"
+#include "download.hh"
+#include "globals.hh"
+#include "parse.hh"
+#include "store-api.hh"
+
+namespace nix::fetchers {
+
+struct TarballInput : Input
+{
+    ParsedURL url;
+    std::optional<Hash> hash;
+
+    bool operator ==(const Input & other) const override
+    {
+        auto other2 = dynamic_cast<const TarballInput *>(&other);
+        return
+            other2
+            && to_string() == other2->to_string()
+            && hash == other2->hash;
+    }
+
+    bool isImmutable() const override
+    {
+        return (bool) hash;
+    }
+
+    std::string to_string() const override
+    {
+        auto url2(url);
+        if (narHash)
+            url2.query.insert_or_assign("narHash", narHash->to_string(SRI));
+        return url2.to_string();
+    }
+
+    std::pair<Tree, std::shared_ptr<const Input>> fetchTreeInternal(nix::ref<Store> store) const override
+    {
+        CachedDownloadRequest request(url.to_string());
+        request.unpack = true;
+        request.getLastModified = true;
+        request.name = "source";
+
+        auto res = getDownloader()->downloadCached(store, request);
+
+        auto input = std::make_shared<TarballInput>(*this);
+
+        auto storePath = store->parseStorePath(res.storePath);
+
+        input->narHash = store->queryPathInfo(storePath)->narHash;
+
+        return {
+            Tree {
+                .actualPath = res.path,
+                .storePath = std::move(storePath),
+                .lastModified = *res.lastModified
+            },
+            input
+        };
+    }
+};
+
+struct TarballInputScheme : InputScheme
+{
+    std::unique_ptr<Input> inputFromURL(const ParsedURL & url) override
+    {
+        if (url.scheme != "file" && url.scheme != "http" && url.scheme != "https") return nullptr;
+
+        if (!hasSuffix(url.path, ".zip")
+            && !hasSuffix(url.path, ".tar")
+            && !hasSuffix(url.path, ".tar.gz")
+            && !hasSuffix(url.path, ".tar.xz")
+            && !hasSuffix(url.path, ".tar.bz2"))
+            return nullptr;
+
+        auto input = std::make_unique<TarballInput>();
+        input->type = "tarball";
+        input->url = url;
+
+        auto narHash = url.query.find("narHash");
+        if (narHash != url.query.end()) {
+            // FIXME: require SRI hash.
+            input->narHash = Hash(narHash->second);
+        }
+
+        return input;
+    }
+};
+
+static auto r1 = OnStartup([] { registerInputScheme(std::make_unique<TarballInputScheme>()); });
+
+}

tests/flakes.sh

@@ -573,3 +573,17 @@ nix flake info --flake-registry $registry --json hg+file://$flake5Dir
 [[ $(nix flake info --flake-registry $registry --json hg+file://$flake5Dir | jq -e -r .revCount) = 1 ]]
 
 nix build -o $TEST_ROOT/result hg+file://$flake5Dir --no-registries --no-allow-dirty
+
+# Test tarball flakes
+tar cfz $TEST_ROOT/flake.tar.gz -C $TEST_ROOT flake5
+
+nix build -o $TEST_ROOT/result file://$TEST_ROOT/flake.tar.gz
+
+# Building with a tarball URL containing a SRI hash should also work.
+url=$(nix flake info --json file://$TEST_ROOT/flake.tar.gz | jq -r .url)
+[[ $url =~ sha256- ]]
+
+nix build -o $TEST_ROOT/result $url
+
+# Building with an incorrect SRI hash should fail.
+nix build -o $TEST_ROOT/result "file://$TEST_ROOT/flake.tar.gz?narHash=sha256-qQ2Zz4DNHViCUrp6gTS7EE4+RMqFQtUfWF2UNUtJKS0=" 2>&1 | grep 'NAR hash mismatch'