From 7d554f295ca0a8947042f367adb4f198730696be Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 1 Jul 2020 14:57:59 +0200
Subject: [PATCH] Support building flakes from a shallow Git repo

Fixes #3756.
---
 src/libexpr/flake/flakeref.cc | 3 +++
 src/libfetchers/git.cc        | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/src/libexpr/flake/flakeref.cc b/src/libexpr/flake/flakeref.cc
index 615269218..701546671 100644
--- a/src/libexpr/flake/flakeref.cc
+++ b/src/libexpr/flake/flakeref.cc
@@ -142,6 +142,9 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
                     parsedURL.query.insert_or_assign("dir", subdir);
                 }
 
+                if (pathExists(flakeRoot + "/.git/shallow"))
+                    parsedURL.query.insert_or_assign("shallow", "1");
+
                 return std::make_pair(
                     FlakeRef(Input::fromURL(parsedURL), get(parsedURL.query, "dir").value_or("")),
                     fragment);
diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index 0b6155e71..5d38e0c2b 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -42,6 +42,8 @@ struct GitInputScheme : InputScheme
         for (auto &[name, value] : url.query) {
             if (name == "rev" || name == "ref")
                 attrs.emplace(name, value);
+            else if (name == "shallow")
+                attrs.emplace(name, Explicit<bool> { value == "1" });
             else
                 url2.query.emplace(name, value);
         }