From b2cc1720f8e8fe9d64549aafa7a26ca70d487a00 Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Fri, 2 Sep 2022 22:03:22 +0800
Subject: [PATCH] Add comment explaining `gcc` exception for undeclared_deps.

---
 Library/Homebrew/extend/os/linux/linkage_checker.rb | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Library/Homebrew/extend/os/linux/linkage_checker.rb b/Library/Homebrew/extend/os/linux/linkage_checker.rb
index 2603ed0d9a..b708cf23a9 100644
--- a/Library/Homebrew/extend/os/linux/linkage_checker.rb
+++ b/Library/Homebrew/extend/os/linux/linkage_checker.rb
@@ -81,6 +81,13 @@ class LinkageChecker
       SYSTEM_LIBRARY_ALLOWLIST.include? File.basename(s)
     end
 
+    # We build all formulae with an RPATH that includes the gcc formula's runtime lib directory.
+    # See: https://github.com/Homebrew/brew/blob/e689cc07/Library/Homebrew/extend/os/linux/extend/ENV/super.rb#L53
+    # This results in formulae showing linkage with gcc whenever it is installed, even if no dependency is declared.
+    # See discussions at:
+    #   https://github.com/Homebrew/brew/pull/13659
+    #   https://github.com/Homebrew/brew/pull/13796
+    # TODO: Find a nicer way to handle this. (e.g. examining the ELF file to determine the required libstdc++.)
     @undeclared_deps.delete("gcc")
   end
 end