Bug 1216901 - Make the FasterMake backend reticulate splines when moz.build or jar.mn files are modified. r=mshal

config/faster/rules.mk

@@ -24,6 +24,8 @@
 # python/mozbuild/mozbuild/backend/fastermake.py is the following:
 # - TOPSRCDIR/TOPOBJDIR, respectively the top source directory and the top
 #   object directory
+# - BACKEND, the path to the file the backend will always update when running
+#   mach build-backend
 # - PYTHON, the path to the python executable
 # - ACDEFINES, which contains a set of -Dvar=name to be used during
 #   preprocessing
@@ -69,12 +71,22 @@ $(TOPOBJDIR)/%: FORCE
 # fallback
 $(TOPOBJDIR)/faster/%: ;
 
+# Files under the python virtualenv, which are dependencies of the BACKEND
+# file, are not meant to use the fallback either.
+$(TOPOBJDIR)/_virtualenv/%: ;
+
 # And files under dist/ are meant to be copied from their first dependency
 # if there is no other rule.
 $(TOPOBJDIR)/dist/%:
 	rm -f $@
 	cp $< $@
 
+# Refresh backend
+$(BACKEND):
+	cd $(TOPOBJDIR) && $(PYTHON) config.status --backend FasterMake
+
+$(MAKEFILE_LIST): $(BACKEND)
+
 # Install files using install manifests
 #
 # The list of base directories is given in INSTALL_MANIFESTS. The

python/mozbuild/mozbuild/backend/fastermake.py

@@ -207,6 +207,7 @@ class FasterMakeBackend(CommonBackend):
         )
         pp.out = JarManifestParser()
         pp.do_include(obj.path)
+        self.backend_input_files |= pp.includes
 
         for jarinfo in pp.out:
             install_target = obj.install_target
@@ -294,6 +295,7 @@ class FasterMakeBackend(CommonBackend):
         mk.create_rule(['default'])
         mk.add_statement('TOPSRCDIR = %s' % self.environment.topsrcdir)
         mk.add_statement('TOPOBJDIR = %s' % self.environment.topobjdir)
+        mk.add_statement('BACKEND = %s' % self._backend_output_list_file)
 
         # Add a few necessary variables inherited from configure
         for var in (
@@ -324,6 +326,10 @@ class FasterMakeBackend(CommonBackend):
             mk.create_rule([target]).add_dependencies(
                 '$(TOPOBJDIR)/%s' % d for d in deps)
 
+        # Add backend dependencies:
+        mk.create_rule([self._backend_output_list_file]).add_dependencies(
+            self.backend_input_files)
+
         mk.add_statement('include $(TOPSRCDIR)/config/faster/rules.mk')
 
         for base, install_manifest in self._install_manifests.iteritems():