From 36f0c546554b25cc06dbfc89d3a9af3237afe658 Mon Sep 17 00:00:00 2001
From: adisbladis <adisbladis@gmail.com>
Date: Fri, 2 Sep 2022 16:34:23 +1200
Subject: [PATCH] Use the highest compatible Go version whenever possible

It should be generally safe to compile any older Go project with a
newer compiler and in the few cases where it isn't it could be
manually passed.
---
 builder/default.nix | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/builder/default.nix b/builder/default.nix
index 44a92ba..3861f3e 100644
--- a/builder/default.nix
+++ b/builder/default.nix
@@ -126,16 +126,22 @@ let
         ''
       );
 
-  # Select Go attribute based on version specified in go.mod
+  # Return a Go attribute and error out if the Go version is older than was specified in go.mod.
   selectGo = attrs: goMod: attrs.go or (if goMod == null then pkgs.go else
   (
     let
       goVersion = goMod.go;
-      goAttr = "go_" + (replaceStrings [ "." ] [ "_" ] goVersion);
+      goAttrs = lib.reverseList (builtins.filter
+        (
+          attr: lib.hasPrefix "go_" attr && lib.versionAtLeast pkgs.${attr}.version goVersion
+        )
+        (lib.attrNames pkgs));
+      goAttr = elemAt goAttrs 0;
     in
     (
-      if hasAttr goAttr pkgs then pkgs.${goAttr}
-      else trace "go.mod specified Go version ${goVersion} but doesn't exist. Falling back to ${pkgs.go.version}." pkgs.go
+      if goAttrs != [ ]
+      then pkgs.${goAttr}
+      else throw "go.mod specified Go version ${goVersion}, but no compatible Go attribute could be found."
     )
   ));