From ee5a1b5a4c53918c029316fb9c961bee58e7d518 Mon Sep 17 00:00:00 2001
From: Qyriad <qyriad@qyriad.me>
Date: Sat, 27 Apr 2024 23:09:02 -0600
Subject: [PATCH] nix3-upgrade-nix: allow manually specifying new nix

This allows manually specifying a store path for the new Nix that
gets linked into Nix's profile.

Change-Id: Ib71711ffb466febf4a6892e3fdbda644e053770d
---
 doc/manual/rl-next/upgrade-nix-override.md |  6 ++++++
 src/nix/upgrade-nix.cc                     | 17 +++++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 doc/manual/rl-next/upgrade-nix-override.md

diff --git a/doc/manual/rl-next/upgrade-nix-override.md b/doc/manual/rl-next/upgrade-nix-override.md
new file mode 100644
index 000000000..d3046ff13
--- /dev/null
+++ b/doc/manual/rl-next/upgrade-nix-override.md
@@ -0,0 +1,6 @@
+---
+synopsis: add --store-path argument to `nix upgrade-nix`, to manually specify the Nix to upgrade to
+cls: 953
+---
+
+`nix upgrade-nix` by default downloads a manifest to find the new Nix version to upgrade to, but now you can specify `--store-path` to upgrade Nix to an arbitrary version from the Nix store.
diff --git a/src/nix/upgrade-nix.cc b/src/nix/upgrade-nix.cc
index 4940d93f8..31a051246 100644
--- a/src/nix/upgrade-nix.cc
+++ b/src/nix/upgrade-nix.cc
@@ -21,6 +21,8 @@ struct CmdUpgradeNix : MixDryRun, EvalCommand
     Path profileDir;
     std::string storePathsUrl = "https://github.com/NixOS/nixpkgs/raw/master/nixos/modules/installer/tools/nix-fallback-paths.nix";
 
+    std::optional<Path> overrideStorePath;
+
     CmdUpgradeNix()
     {
         addFlag({
@@ -31,6 +33,13 @@ struct CmdUpgradeNix : MixDryRun, EvalCommand
             .handler = {&profileDir}
         });
 
+        addFlag({
+            .longName = "store-path",
+            .description = "A specific store path to upgrade Nix to",
+            .labels = {"store-path"},
+            .handler = {&overrideStorePath},
+        });
+
         addFlag({
             .longName = "nix-store-paths-url",
             .description = "The URL of the file that contains the store paths of the latest Nix release.",
@@ -246,6 +255,14 @@ struct CmdUpgradeNix : MixDryRun, EvalCommand
     /* Return the store path of the latest stable Nix. */
     StorePath getLatestNix(ref<Store> store)
     {
+        if (this->overrideStorePath) {
+            printTalkative(
+                "skipping Nix version query and using '%s' as latest Nix",
+                *this->overrideStorePath
+            );
+            return store->parseStorePath(*this->overrideStorePath);
+        }
+
         Activity act(*logger, lvlInfo, actUnknown, "querying latest Nix version");
 
         // FIXME: use nixos.org?