Prevent deps of build-time deps from leaking into the build environment

When decided what dependencies should be part of the build environment
(and have appropriate entries added to variables like PKG_CONFIG_PATH),
we select the entire dependency tree except for

 (1) inactive optional and recommended deps (2) indirect build-time deps
 (i.e., build-time deps of other deps)

There is a third category that sould be excluded: dependencies of direct
build-time deps. These are irrelevant to the build, and including them
can cause unexpected linkages.

1 files changed, 7 insertions, 0 deletions

diff --git a/Library/Homebrew/dependency.rb b/Library/Homebrew/dependency.rb
index df22eed90..fda491b99 100644
--- a/Library/Homebrew/dependency.rb
+++ b/Library/Homebrew/dependency.rb
@@ -82,6 +82,8 @@ class Dependency
           next []
         when :skip
           expand(dep.to_formula, &block)
+        when :keep_but_prune_recursive_deps
+          [dep]
         else
           expand(dep.to_formula, &block) << dep
         end
@@ -110,6 +112,11 @@ class Dependency
       throw(:action, :skip)
     end
 
+    # Keep a dependency, but prune its dependencies
+    def keep_but_prune_recursive_deps
+      throw(:action, :keep_but_prune_recursive_deps)
+    end
+
     def merge_repeats(deps)
       grouped = deps.group_by(&:name)