Add date of last commit to SourceInfo

This is primarily useful for version string generation, where we need
a monotonically increasing number. The revcount is the preferred thing
to use, but isn't available for GitHub flakes (since it requires
fetching the entire history). The last commit timestamp OTOH can be
extracted from GitHub tarballs.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/libexpr/primops/fetchGit.cc b/src/libexpr/primops/fetchGit.cc
index f6b096c4a..10f6b6f72 100644
--- a/src/libexpr/primops/fetchGit.cc
+++ b/src/libexpr/primops/fetchGit.cc
@@ -69,6 +69,9 @@ GitInfo exportGit(ref<Store> store, std::string uri,
 
             gitInfo.storePath = store->addToStore("source", uri, true, htSHA256, filter);
             gitInfo.revCount = std::stoull(runProgram("git", true, { "-C", uri, "rev-list", "--count", "HEAD" }));
+            // FIXME: maybe we should use the timestamp of the last
+            // modified dirty file?
+            gitInfo.lastModified = std::stoull(runProgram("git", true, { "-C", uri, "show", "-s", "--format=%ct", "HEAD" }));
 
             return gitInfo;
         }
@@ -85,8 +88,9 @@ GitInfo exportGit(ref<Store> store, std::string uri,
     }
 
     deletePath(getCacheDir() + "/nix/git");
+    deletePath(getCacheDir() + "/nix/gitv2");
 
-    Path cacheDir = getCacheDir() + "/nix/gitv2/" + hashString(htSHA256, uri).to_string(Base32, false);
+    Path cacheDir = getCacheDir() + "/nix/gitv3/" + hashString(htSHA256, uri).to_string(Base32, false);
     Path repoDir;
 
     if (isLocal) {
@@ -181,6 +185,7 @@ GitInfo exportGit(ref<Store> store, std::string uri,
         if (store->isValidPath(storePath)) {
             gitInfo.storePath = storePath;
             gitInfo.revCount = json["revCount"];
+            gitInfo.lastModified = json["lastModified"];
             return gitInfo;
         }
 
@@ -200,6 +205,7 @@ GitInfo exportGit(ref<Store> store, std::string uri,
     gitInfo.storePath = store->addToStore(name, tmpDir);
 
     gitInfo.revCount = std::stoull(runProgram("git", true, { "-C", repoDir, "rev-list", "--count", gitInfo.rev.gitRev() }));
+    gitInfo.lastModified = std::stoull(runProgram("git", true, { "-C", repoDir, "show", "-s", "--format=%ct", gitInfo.rev.gitRev() }));
 
     nlohmann::json json;
     json["storePath"] = gitInfo.storePath;
@@ -207,6 +213,7 @@ GitInfo exportGit(ref<Store> store, std::string uri,
     json["name"] = name;
     json["rev"] = gitInfo.rev.gitRev();
     json["revCount"] = gitInfo.revCount;
+    json["lastModified"] = gitInfo.lastModified;
 
     writeFile(storeLink, json.dump());