From 1a81257721fd67ed376bd0a2b3a7dc7258b681ca Mon Sep 17 00:00:00 2001
From: Bo Anderson <mail@boanderson.me>
Date: Wed, 14 Apr 2021 16:37:11 +0100
Subject: [PATCH] build: set SOURCE_DATE_EPOCH

---
 Library/Homebrew/build.rb | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Library/Homebrew/build.rb b/Library/Homebrew/build.rb
index 655e0206c7..d860f2808d 100644
--- a/Library/Homebrew/build.rb
+++ b/Library/Homebrew/build.rb
@@ -144,6 +144,9 @@ class Build
         # which is not known until after the formula has been staged.
         ENV["HOMEBREW_FORMULA_PREFIX"] = formula.prefix
 
+        # https://reproducible-builds.org/docs/source-date-epoch/
+        ENV["SOURCE_DATE_EPOCH"] = formula.source_modified_time.to_i.to_s
+
         formula.patch
 
         if args.git?