From ef7c9cf17cf4c65bc198d77d7957b631f58aaea8 Mon Sep 17 00:00:00 2001
From: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Date: Fri, 2 Sep 2022 14:28:07 +0800
Subject: [PATCH 1/2] linux/linkage_checker: remove `gcc` from
 `undeclared_deps`

This is causing warnings all over Homebrew/homebrew-core.

For example, there are dozens of warnings about this in the following CI
run:

    https://github.com/Homebrew/homebrew-core/runs/8116257943?check_suite_focus=true
---
 Library/Homebrew/extend/os/linux/linkage_checker.rb | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Library/Homebrew/extend/os/linux/linkage_checker.rb b/Library/Homebrew/extend/os/linux/linkage_checker.rb
index 583107d85e..2603ed0d9a 100644
--- a/Library/Homebrew/extend/os/linux/linkage_checker.rb
+++ b/Library/Homebrew/extend/os/linux/linkage_checker.rb
@@ -80,5 +80,7 @@ class LinkageChecker
     @unwanted_system_dylibs = @system_dylibs.reject do |s|
       SYSTEM_LIBRARY_ALLOWLIST.include? File.basename(s)
     end
+
+    @undeclared_deps.delete("gcc")
   end
 end

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 2/2] 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