From 4e37d03ba265234fe56a7da1e07251d3ec2867d5 Mon Sep 17 00:00:00 2001
From: Yueh-Shun Li <shamrocklee@posteo.net>
Date: Sat, 22 Nov 2025 06:14:29 +0800
Subject: [PATCH] fetchgit: reference hash from finalAttrs.hash

---
 pkgs/build-support/fetchgit/default.nix | 22 ++++++++++--
 pkgs/test/overriding.nix                | 46 +++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/pkgs/build-support/fetchgit/default.nix b/pkgs/build-support/fetchgit/default.nix
index 7a8f689df439..2a175a71ccd2 100644
--- a/pkgs/build-support/fetchgit/default.nix
+++ b/pkgs/build-support/fetchgit/default.nix
@@ -47,7 +47,7 @@ lib.makeOverridable (
 
       # Hashes, handled by `lib.fetchers.withNormalizedHash`
       # whose outputs contain outputHash* attributes.
-      "hash"
+      # Use `hash` when overriding with `<pkg>.overrideAttrs`.
       "sha256"
     ];
 
@@ -131,6 +131,11 @@ lib.makeOverridable (
           server admins start using the new version?
         */
 
+        let
+          finalHashHasColon = lib.hasInfix ":" finalAttrs.hash;
+          finalHashColonMatch = lib.match "([^:]+)[:](.*)" finalAttrs.hash;
+        in
+
         derivationArgs
         // {
           inherit name;
@@ -145,7 +150,20 @@ lib.makeOverridable (
           ++ lib.optionals fetchLFS [ git-lfs ]
           ++ nativeBuildInputs;
 
-          inherit outputHash outputHashAlgo;
+          hash =
+            if outputHashAlgo == null || outputHash == "" || lib.hasPrefix outputHashAlgo outputHash then
+              outputHash
+            else
+              "${outputHashAlgo}:${outputHash}";
+
+          outputHash =
+            if finalAttrs.hash == "" then
+              lib.fakeHash
+            else if finalHashHasColon then
+              lib.elemAt finalHashColonMatch 1
+            else
+              finalAttrs.hash;
+          outputHashAlgo = if finalHashHasColon then lib.head finalHashColonMatch else null;
           outputHashMode = "recursive";
 
           sparseCheckout =
diff --git a/pkgs/test/overriding.nix b/pkgs/test/overriding.nix
index 2ee08e590408..3daa01b6247d 100644
--- a/pkgs/test/overriding.nix
+++ b/pkgs/test/overriding.nix
@@ -137,6 +137,52 @@ let
       };
     };
 
+  tests-fetchgit =
+    let
+      src-with-sha256 = pkgs.fetchgit {
+        url = "https://example.com/source.git";
+        sha256 = lib.fakeSha256;
+      };
+    in
+    {
+      test-fetchgit-hash-compat = {
+        expr = {
+          inherit (src-with-sha256)
+            outputHash
+            outputHashAlgo
+            ;
+        };
+        expected = {
+          outputHash = lib.fakeSha256;
+          outputHashAlgo = "sha256";
+        };
+      };
+      test-fetchgit-overrideAttrs-hash = {
+        expr = {
+          inherit (src-with-sha256.overrideAttrs { hash = pkgs.nix.src.hash; })
+            outputHash
+            outputHashAlgo
+            ;
+        };
+        expected = {
+          outputHash = pkgs.nix.src.hash;
+          outputHashAlgo = null;
+        };
+      };
+      test-fetchurl-overrideAttrs-hash-empty = {
+        expr = {
+          inherit (src-with-sha256.overrideAttrs { hash = ""; })
+            outputHash
+            outputHashAlgo
+            ;
+        };
+        expected = {
+          outputHash = lib.fakeHash;
+          outputHashAlgo = null;
+        };
+      };
+    };
+
   tests-fetchurl =
     let
       src-with-sha256 = pkgs.fetchurl {