Add cxxstdlib_check method to request changing C++ stdlib checking.

* In certain cases, a C++ software may result in linking to a different
  and incompatible C++ standard library than its dependencies and still
  works fine because it is by design. Examples include GCC, which will
  bootstrap itself and self-host after finish.

* Add a cxxstdlib_check method to formula to request changing the C++
  standard library checking. Currently using "cxxstdlib_check :skip"
  will let a formula skip such checking. This should only be used on
  rare occasions and be very careful.

Closes Homebrew/homebrew#23687.

1 files changed, 11 insertions, 8 deletions

diff --git a/Library/Homebrew/cxxstdlib.rb b/Library/Homebrew/cxxstdlib.rb
index 2b4ec5827..fba868277 100644
--- a/Library/Homebrew/cxxstdlib.rb
+++ b/Library/Homebrew/cxxstdlib.rb
@@ -33,14 +33,17 @@ class CxxStdlib
   end
 
   def check_dependencies(formula, deps)
-    deps.each do |dep|
-      # Software is unlikely to link against anything from its buildtime deps,
-      # so it doesn't matter at all if they link against different C++ stdlibs
-      next if dep.tags.include? :build
-
-      dep_stdlib = Tab.for_formula(dep.to_formula).cxxstdlib
-      if !compatible_with? dep_stdlib
-        raise IncompatibleCxxStdlibs.new(formula, dep, dep_stdlib, self)
+    unless formula.cxxstdlib.include? :skip
+      deps.each do |dep|
+        # Software is unlikely to link against anything from its
+        # buildtime deps, so it doesn't matter at all if they link
+        # against different C++ stdlibs
+        next if dep.tags.include? :build
+
+        dep_stdlib = Tab.for_formula(dep.to_formula).cxxstdlib
+        if !compatible_with? dep_stdlib
+          raise IncompatibleCxxStdlibs.new(formula, dep, dep_stdlib, self)
+        end
       end
     end
   end