From a39526b3ef4488fdb98eabb0cef0985e671a2b5c Mon Sep 17 00:00:00 2001
From: dev-null-undefined <martinkos007@gmail.com>
Date: Thu, 27 Jul 2023 15:29:57 +0200
Subject: [PATCH] nixos/grub: Add submenu for each generation with
 specialisation

Before this commit there was no way to access (boot into) specialisation of previous generations from grub,even tho they are there.

This commit will add grub submenu for each generation if the generation has any specialisation.
Which will allow you to boot into them.

Co-authored-by: Samuel Dionne-Riel <samuel@dionne-riel.com>
---
 .../system/boot/loader/grub/install-grub.pl   | 67 ++++++++++++-------
 1 file changed, 41 insertions(+), 26 deletions(-)

diff --git a/nixos/modules/system/boot/loader/grub/install-grub.pl b/nixos/modules/system/boot/loader/grub/install-grub.pl
index a84e374624d1..d1e7a0cb8178 100644
--- a/nixos/modules/system/boot/loader/grub/install-grub.pl
+++ b/nixos/modules/system/boot/loader/grub/install-grub.pl
@@ -516,38 +516,53 @@ sub addEntry {
     $conf .= "}\n\n";
 }
 
+sub addGeneration {
+    my ($name, $nameSuffix, $path, $options, $current) = @_;
+
+    # Do not search for grand children
+    my @links = sort (glob "$path/specialisation/*");
+
+    if ($current != 1 && scalar(@links) != 0) {
+        $conf .= "submenu \"> $name$nameSuffix\" --class submenu {\n";
+    }
+
+    addEntry("$name" . (scalar(@links) == 0 ? "" : " - Default") . $nameSuffix, $path, $options, $current);
+
+    # Find all the children of the current default configuration
+    # Do not search for grand children
+    foreach my $link (@links) {
+
+        my $entryName = "";
+
+        my $cfgName = readFile("$link/configuration-name");
+
+        my $date = strftime("%F", localtime(lstat($link)->mtime));
+        my $version =
+            -e "$link/nixos-version"
+            ? readFile("$link/nixos-version")
+            : basename((glob(dirname(Cwd::abs_path("$link/kernel")) . "/lib/modules/*"))[0]);
+
+        if ($cfgName) {
+            $entryName = $cfgName;
+        } else {
+            my $linkname = basename($link);
+            $entryName = "($linkname - $date - $version)";
+        }
+        addEntry("$name - $entryName", $link, "", 1);
+    }
+
+    if ($current != 1 && scalar(@links) != 0) {
+        $conf .= "}\n";
+    }
+}
 
 # Add default entries.
 $conf .= "$extraEntries\n" if $extraEntriesBeforeNixOS;
 
-addEntry("@distroName@ - Default", $defaultConfig, $entryOptions, 1);
+addGeneration("@distroName@", "", $defaultConfig, $entryOptions, 1);
 
 $conf .= "$extraEntries\n" unless $extraEntriesBeforeNixOS;
 
-# Find all the children of the current default configuration
-# Do not search for grand children
-my @links = sort (glob "$defaultConfig/specialisation/*");
-foreach my $link (@links) {
-
-    my $entryName = "";
-
-    my $cfgName = readFile("$link/configuration-name");
-
-    my $date = strftime("%F", localtime(lstat($link)->mtime));
-    my $version =
-        -e "$link/nixos-version"
-        ? readFile("$link/nixos-version")
-        : basename((glob(dirname(Cwd::abs_path("$link/kernel")) . "/lib/modules/*"))[0]);
-
-    if ($cfgName) {
-        $entryName = $cfgName;
-    } else {
-        my $linkname = basename($link);
-        $entryName = "($linkname - $date - $version)";
-    }
-    addEntry("@distroName@ - $entryName", $link, "", 1);
-}
-
 my $grubBootPath = $grubBoot->path;
 # extraEntries could refer to @bootRoot@, which we have to substitute
 $conf =~ s/\@bootRoot\@/$grubBootPath/g;
@@ -577,7 +592,7 @@ sub addProfile {
             -e "$link/nixos-version"
             ? readFile("$link/nixos-version")
             : basename((glob(dirname(Cwd::abs_path("$link/kernel")) . "/lib/modules/*"))[0]);
-        addEntry("@distroName@ - Configuration " . nrFromGen($link) . " ($date - $version)", $link, $subEntryOptions, 0);
+        addGeneration("@distroName@ - Configuration " . nrFromGen($link), " ($date - $version)", $link, $subEntryOptions, 0);
     }
 
     $conf .= "}\n";