Switch to libgit2 experimental

Just patch the package for now, but we should make Nixpkgs provide what
we need (whether that the experimental variant, or a 2.x release with
the new API made non-experimental) before releasing this change.

packaging/dependencies.nix

@@ -74,4 +74,14 @@ scope: {
         buildPhase = lib.replaceStrings [ "--without-python" ] [ "" ] old.buildPhase;
         installPhase = lib.replaceStrings [ "--without-python" ] [ "" ] old.installPhase;
       });
+
+  libgit2 = pkgs.libgit2.overrideAttrs (attrs: {
+    cmakeFlags = (attrs.cmakeFlags or [ ]) ++ [
+      (lib.mesonBool "EXPERIMENTAL_SHA256" true)
+    ];
+
+    postInstall = (attrs.postInstall or "") + ''
+      substituteInPlace $(find $dev/include -type f) --replace-quiet '#include "git2/' '#include "git2-experimental/'
+    '';
+  });
 }

src/libfetchers-tests/git-utils.cc

@@ -1,19 +1,19 @@
 #include "nix/fetchers/git-utils.hh"
 #include "nix/util/file-system.hh"
 #include <gmock/gmock.h>
-#include <git2/global.h>
+#include <git2-experimental/global.h>
-#include <git2/repository.h>
+#include <git2-experimental/repository.h>
-#include <git2/signature.h>
+#include <git2-experimental/signature.h>
-#include <git2/types.h>
+#include <git2-experimental/types.h>
-#include <git2/object.h>
+#include <git2-experimental/object.h>
-#include <git2/tag.h>
+#include <git2-experimental/tag.h>
 #include <gtest/gtest.h>
 #include "nix/util/fs-sink.hh"
 #include "nix/util/serialise.hh"
 #include "nix/fetchers/git-lfs-fetch.hh"
 
-#include <git2/blob.h>
+#include <git2-experimental/blob.h>
-#include <git2/tree.h>
+#include <git2-experimental/tree.h>
 
 namespace nix {
 

src/libfetchers-tests/git.cc

@@ -5,7 +5,7 @@
 #include "nix/fetchers/fetchers.hh"
 #include "nix/fetchers/git-utils.hh"
 
-#include <git2.h>
+#include <git2-experimental.h>
 #include <gtest/gtest.h>
 
 #include <filesystem>

src/libfetchers-tests/meson.build

@@ -33,7 +33,7 @@ deps_private += rapidcheck
 gtest = dependency('gtest', main : true)
 deps_private += gtest
 
-libgit2 = dependency('libgit2')
+libgit2 = dependency('libgit2-experimental')
 deps_private += libgit2
 
 subdir('nix-meson-build-support/common')

src/libfetchers/git-lfs-fetch.cc

@@ -7,10 +7,10 @@
 #include "nix/util/hash.hh"
 #include "nix/store/ssh.hh"
 
-#include <git2/attr.h>
+#include <git2-experimental/attr.h>
-#include <git2/config.h>
+#include <git2-experimental/config.h>
-#include <git2/errors.h>
+#include <git2-experimental/errors.h>
-#include <git2/remote.h>
+#include <git2-experimental/remote.h>
 
 #include <nlohmann/json.hpp>
 

src/libfetchers/git-utils.cc

@@ -13,27 +13,27 @@
 #include "nix/util/thread-pool.hh"
 #include "nix/util/pool.hh"
 
-#include <git2/attr.h>
+#include <git2-experimental/attr.h>
-#include <git2/blob.h>
+#include <git2-experimental/blob.h>
-#include <git2/branch.h>
+#include <git2-experimental/branch.h>
-#include <git2/commit.h>
+#include <git2-experimental/commit.h>
-#include <git2/config.h>
+#include <git2-experimental/config.h>
-#include <git2/describe.h>
+#include <git2-experimental/describe.h>
-#include <git2/errors.h>
+#include <git2-experimental/errors.h>
-#include <git2/global.h>
+#include <git2-experimental/global.h>
-#include <git2/indexer.h>
+#include <git2-experimental/indexer.h>
-#include <git2/object.h>
+#include <git2-experimental/object.h>
-#include <git2/odb.h>
+#include <git2-experimental/odb.h>
-#include <git2/refs.h>
+#include <git2-experimental/refs.h>
-#include <git2/remote.h>
+#include <git2-experimental/remote.h>
-#include <git2/repository.h>
+#include <git2-experimental/repository.h>
-#include <git2/revparse.h>
+#include <git2-experimental/revparse.h>
-#include <git2/status.h>
+#include <git2-experimental/status.h>
-#include <git2/submodule.h>
+#include <git2-experimental/submodule.h>
-#include <git2/sys/odb_backend.h>
+#include <git2-experimental/sys/odb_backend.h>
-#include <git2/sys/mempack.h>
+#include <git2-experimental/sys/mempack.h>
-#include <git2/tag.h>
+#include <git2-experimental/tag.h>
-#include <git2/tree.h>
+#include <git2-experimental/tree.h>
 
 #include <boost/unordered/concurrent_flat_set.hpp>
 #include <boost/unordered/unordered_flat_map.hpp>

src/libfetchers/include/nix/fetchers/git-lfs-fetch.hh

@@ -5,7 +5,7 @@
 #include "nix/util/serialise.hh"
 #include "nix/util/url.hh"
 
-#include <git2/repository.h>
+#include <git2-experimental/repository.h>
 
 #include <nlohmann/json_fwd.hpp>
 

src/libfetchers/meson.build

@@ -28,7 +28,7 @@ subdir('nix-meson-build-support/subprojects')
 nlohmann_json = dependency('nlohmann_json', version : '>= 3.9')
 deps_public += nlohmann_json
 
-libgit2 = dependency('libgit2', version : '>= 1.9')
+libgit2 = dependency('libgit2-experimental', version : '>= 1.9')
 deps_private += libgit2
 
 subdir('nix-meson-build-support/common')