ENV: allow a user-configurable number of make jobs

Let an environment variable, HOMEBREW_MAKE_JOBS, override the default
'-j<cores>' make flag.

Now we can more easily debug formula that normally build in parallel, or
(potentially) speed up lengthy builds.

1 files changed, 10 insertions, 1 deletions

diff --git a/Library/Homebrew/extend/ENV.rb b/Library/Homebrew/extend/ENV.rb
index 931f69271..8ca166ac0 100644
--- a/Library/Homebrew/extend/ENV.rb
+++ b/Library/Homebrew/extend/ENV.rb
@@ -8,7 +8,7 @@ module HomebrewEnvExtension
     delete('CPPFLAGS')
     delete('LDFLAGS')
 
-    self['MAKEFLAGS'] = "-j#{Hardware.processor_count}"
+    self['MAKEFLAGS'] = "-j#{self.make_jobs}"
 
     unless HOMEBREW_PREFIX.to_s == '/usr/local'
       # /usr/local is already an -isystem and -L directory so we skip it
@@ -309,4 +309,13 @@ Please take one of the following actions:
   def use_llvm?
     self['HOMEBREW_USE_LLVM'] or ARGV.include? '--use-llvm'
   end
+
+  def make_jobs
+    # '-j' requires a positive integral argument
+    if self['HOMEBREW_MAKE_JOBS'].to_i > 0
+      self['HOMEBREW_MAKE_JOBS']
+    else
+      Hardware.processor_count
+    end
+  end
 end