From 22db7aa516ef385949582cac1f12d8984e441f8b Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Thu, 16 Sep 2021 21:11:12 +0800
Subject: [PATCH] superenv: set `M4` on Linux when `bison` is a dependency

Bison no longer remembers the path to `m4` as of
Homebrew/homebrew-core#84931. Since superenv does not put runtime
dependencies of build dependences in `PATH`, we now need to help Bison
find `m4` by setting `M4` in the environment.

See also Homebrew/homebrew-core#85260.
---
 Library/Homebrew/extend/os/linux/extend/ENV/super.rb | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Library/Homebrew/extend/os/linux/extend/ENV/super.rb b/Library/Homebrew/extend/os/linux/extend/ENV/super.rb
index 27b0a292a4..c2dd76f414 100644
--- a/Library/Homebrew/extend/os/linux/extend/ENV/super.rb
+++ b/Library/Homebrew/extend/os/linux/extend/ENV/super.rb
@@ -24,6 +24,7 @@ module Superenv
     self["HOMEBREW_OPTIMIZATION_LEVEL"] = "O2"
     self["HOMEBREW_DYNAMIC_LINKER"] = determine_dynamic_linker_path
     self["HOMEBREW_RPATH_PATHS"] = determine_rpath_paths(@formula)
+    self["M4"] = "#{HOMEBREW_PREFIX}/opt/m4/bin/m4" if deps.any? { |d| d.name == "libtool" || d.name == "bison" }
   end
 
   def homebrew_extra_paths