From a3fd89f1bbb03bb580fd47f1ee7daa9018bba7cb Mon Sep 17 00:00:00 2001
From: Malo Bourgon <mbourgon@gmail.com>
Date: Mon, 9 Feb 2026 19:36:07 -0800
Subject: [PATCH] modules/homebrew: add `link: :overwrite` support

Homebrew supports `link: :overwrite` which runs `brew link --overwrite`,
force-overwriting existing symlinks. Extract the existing
`restart_service` special-case logic into a reusable helper
(`mkBrewfileLineBoolOrSymbolString`) for options that can be either a
bool or a Ruby symbol in the Brewfile.
---
 modules/homebrew.nix | 34 ++++++++++++++++++++--------------
 tests/homebrew.nix   |  7 ++++---
 2 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/modules/homebrew.nix b/modules/homebrew.nix
index eba43c6..61fb5c8 100644
--- a/modules/homebrew.nix
+++ b/modules/homebrew.nix
@@ -28,6 +28,15 @@ let
   mkBrewfileLineOptionsListString = attrs:
     concatStringsSep ", " (mapAttrsToList (n: v: "${n}: ${v}") attrs);
 
+  # Renders a Brewfile option that can be either a bool or a Ruby symbol (e.g. `:overwrite`).
+  mkBrewfileLineBoolOrSymbolString = name: config: sCfg:
+    optionalString (hasAttr name sCfg) (
+      ", ${name}: " + (
+        if isBool config.${name} then sCfg.${name}
+        else ":${config.${name}}"
+      )
+    );
+
 
   # Option and submodule helper functions ----------------------------------------------------------
 
@@ -456,12 +465,15 @@ let
           Homebrew's default is `false`.
         '';
       };
-      link = mkNullOrBoolOption {
+      link = mkOption {
+        type = with types; nullOr (either bool (enum [ "overwrite" ]));
+        default = null;
         description = ''
-          Whether to link the formula to the Homebrew prefix. When this option is
-          `null`, Homebrew will use it's default behavior which is to link the
-          formula if it's currently unlinked and not keg-only, and to unlink the formula if it's
-          currently linked and keg-only.
+          Whether to link the formula to the Homebrew prefix. When set to `"overwrite"`,
+          existing symlinks will be overwritten ({command}`brew link --overwrite`). When this
+          option is `null`, Homebrew will use its default behavior which is to link the formula
+          if it's currently unlinked and not keg-only, and to unlink the formula if it's currently
+          linked and keg-only.
         '';
       };
 
@@ -471,20 +483,14 @@ let
     config =
       let
         sCfg = mkProcessedSubmodConfig config;
-        sCfgSubset = removeAttrs sCfg [ "name" "restart_service" ];
+        sCfgSubset = removeAttrs sCfg [ "name" "restart_service" "link" ];
       in
       {
         brewfileLine =
           "brew ${sCfg.name}"
           + optionalString (sCfgSubset != { }) ", ${mkBrewfileLineOptionsListString sCfgSubset}"
-          # We need to handle the `restart_service` option seperately since it can be either a bool
-          # or `:changed` in the Brewfile.
-          + optionalString (sCfg ? restart_service) (
-            ", restart_service: " + (
-              if isBool config.restart_service then sCfg.restart_service
-              else ":${config.restart_service}"
-            )
-          );
+          + mkBrewfileLineBoolOrSymbolString "link" config sCfg
+          + mkBrewfileLineBoolOrSymbolString "restart_service" config sCfg;
       };
   };
 
diff --git a/tests/homebrew.nix b/tests/homebrew.nix
index 64e52c4..7815158 100644
--- a/tests/homebrew.nix
+++ b/tests/homebrew.nix
@@ -17,7 +17,7 @@ in
 
   homebrew.user = "test-homebrew-user";
 
-  # Examples taken from https://github.com/Homebrew/homebrew-bundle
+  # Examples adapted from https://docs.brew.sh/Brew-Bundle-and-Brewfile
   homebrew.taps = [
     "homebrew/cask"
     {
@@ -41,7 +41,8 @@ in
     {
       name = "denji/nginx/nginx-full";
       args = [ "with-rmtp" ];
-      restart_service = "changed";
+      link = "overwrite";
+      restart_service = "always";
     }
     {
       name = "mysql@5.6";
@@ -89,7 +90,7 @@ in
 
     echo "checking brew entries in Brewfile" >&2
     ${mkTest "imagemagick" ''brew "imagemagick"''}
-    ${mkTest "denji/nginx/nginx-full" ''brew "denji/nginx/nginx-full", args: ["with-rmtp"], restart_service: :changed''}
+    ${mkTest "denji/nginx/nginx-full" ''brew "denji/nginx/nginx-full", args: ["with-rmtp"], link: :overwrite, restart_service: :always''}
     ${mkTest "mysql@5.6" ''brew "mysql@5.6", conflicts_with: ["mysql"], link: true, restart_service: true''}
 
     echo "checking cask entries in Brewfile" >&2