Improve generated Makefile rules for rules with 2 outputs.

pylib/gyp/generator/make.py

 # Copyright (c) 2013 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Notes:
 #
 # This is all roughly based on the Makefile system used by the Linux
 # kernel, but is a non-recursive make -- we put the entire dependency
 # graph in front of make and let it figure it out.
 #
@@ skipping 1001 matching lines @@
         outputs = [gyp.xcode_emulation.ExpandEnvVars(o, env) for o in outputs]
         inputs = [gyp.xcode_emulation.ExpandEnvVars(i, env) for i in inputs]
 
         outputs = map(self.Absolutify, outputs)
         all_outputs += outputs
         # Only write the 'obj' and 'builddir' rules for the "primary" output
         # (:1); it's superfluous for the "extra outputs", and this avoids
         # accidentally writing duplicate dummy rules for those outputs.
         self.WriteLn('%s: obj := $(abs_obj)' % outputs[0])
         self.WriteLn('%s: builddir := $(abs_builddir)' % outputs[0])
-        self.WriteMakeRule(outputs, inputs + ['FORCE_DO_CMD'], actions)
+        self.WriteMakeRule(outputs, inputs, actions,
+                           command="%s_%d" % (name, count))
         # Spaces in rule filenames are not supported, but rule variables have
         # spaces in them (e.g. RULE_INPUT_PATH expands to '$(abspath $<)').
         # The spaces within the variables are valid, so remove the variables
         # before checking.
         variables_with_spaces = re.compile(r'\$\([^ ]* \$<\)')
         for output in outputs:
           output = re.sub(variables_with_spaces, '', output)
           assert ' ' not in output, (
               "Spaces in rule filenames not yet supported (%s)"  % output)
         self.WriteLn('all_deps += %s' % ' '.join(outputs))
@@ skipping 648 matching lines @@
     This makes the outputs dependent on the command line that was run,
     as well as support the V= make command line flag.
     """
     suffix = ''
     if postbuilds:
       assert ',' not in command
       suffix = ',,1'  # Tell do_cmd to honor $POSTBUILDS
     self.WriteMakeRule(outputs, inputs,
                        actions = ['$(call do_cmd,%s%s)' % (command, suffix)],
                        comment = comment,
+                       command = command,
                        force = True)
     # Add our outputs to the list of targets we read depfiles from.
     # all_deps is only used for deps file reading, and for deps files we replace
     # spaces with ? because escaping doesn't work with make's $(sort) and
     # other functions.
     outputs = [QuoteSpaces(o, SPACE_REPLACEMENT) for o in outputs]
     self.WriteLn('all_deps += %s' % ' '.join(outputs))
 
 
   def WriteMakeRule(self, outputs, inputs, actions=None, comment=None,
-                    order_only=False, force=False, phony=False):
+                    order_only=False, force=False, phony=False, command=None):
     """Write a Makefile rule, with some extra tricks.
 
     outputs: a list of outputs for the rule (note: this is not directly
              supported by make; see comments below)
     inputs: a list of inputs for the rule
     actions: a list of shell commands to run for the rule
     comment: a comment to put in the Makefile above the rule (also useful
              for making this Python script's code self-documenting)
     order_only: if true, makes the dependency order-only
     force: if true, include FORCE_DO_CMD as an order-only dep
     phony: if true, the rule does not actually generate the named output, the
            output is just a name to run the rule
+    command: (optional) command name to generate unambiguous labels
     """
     outputs = map(QuoteSpaces, outputs)
     inputs = map(QuoteSpaces, inputs)
 
     if comment:
       self.WriteLn('# ' + comment)
     if phony:
       self.WriteLn('.PHONY: ' + ' '.join(outputs))
-    # TODO(evanm): just make order_only a list of deps instead of these hacks.
-    if order_only:
-      order_insert = '| '
-      pick_output = ' '.join(outputs)
-    else:
-      order_insert = ''
-      pick_output = outputs[0]
-    if force:
-      force_append = ' FORCE_DO_CMD'
-    else:
-      force_append = ''
     if actions:
       self.WriteLn("%s: TOOLSET := $(TOOLSET)" % outputs[0])
-    self.WriteLn('%s: %s%s%s' % (pick_output, order_insert, ' '.join(inputs),
-                                 force_append))
+    force_append = ' FORCE_DO_CMD' if force else ''
+
+    if order_only:
+      # Order only rule: Just write a simple rule.
+      # TODO(evanm): just make order_only a list of deps instead of this hack.
+      self.WriteLn('%s: | %s%s' %
+                   (' '.join(outputs), ' '.join(inputs), force_append))
+    elif len(outputs) == 1:
+      # Regular rule, one output: Just write a simple rule.
+      self.WriteLn('%s: %s%s' % (outputs[0], ' '.join(inputs), force_append))
+    else:
+      # Regular rule, more than one output: Multiple outputs are tricky in
+      # make. We will write three rules:
+      # - All outputs depend on an intermediate file.
+      # - Make .INTERMEDIATE depend on the intermediate.
+      # - The intermediate file depends on the inputs and executes the
+      #   actual command.
+      #
+      # For an explanation of the problem and several solutions that don't
+      # work, see this:
+      # http://www.gnu.org/software/hello/manual/automake/Multiple-Outputs.html
+      intermediate = "%s.intermediate" % (command if command else self.target)
+      self.WriteLn('%s: %s' % (' '.join(outputs), intermediate))
+      self.WriteLn('%s: %s' % ('.INTERMEDIATE', intermediate))
+      self.WriteLn('%s: %s%s' %
+                   (intermediate, ' '.join(inputs), force_append))
+
     if actions:
       for action in actions:
         self.WriteLn('\t%s' % action)
-    if not order_only and len(outputs) > 1:
-      # If we have more than one output, a rule like
-      #   foo bar: baz
-      # that for *each* output we must run the action, potentially
-      # in parallel.  That is not what we're trying to write -- what
-      # we want is that we run the action once and it generates all
-      # the files.
-      # http://www.gnu.org/software/hello/manual/automake/Multiple-Outputs.html
-      # discusses this problem and has this solution:
-      # 1) Write the naive rule that would produce parallel runs of
-      # the action.
-      # 2) Make the outputs seralized on each other, so we won't start
-      # a parallel run until the first run finishes, at which point
-      # we'll have generated all the outputs and we're done.
-      self.WriteLn('%s: %s' % (' '.join(outputs[1:]), outputs[0]))
-      # Add a dummy command to the "extra outputs" rule, otherwise make seems to
-      # think these outputs haven't (couldn't have?) changed, and thus doesn't
-      # flag them as changed (i.e. include in '$?') when evaluating dependent
-      # rules, which in turn causes do_cmd() to skip running dependent commands.
-      self.WriteLn('%s: ;' % (' '.join(outputs[1:])))
     self.WriteLn()
 
 
   def WriteAndroidNdkModuleRule(self, module_name, all_sources, link_deps):
     """Write a set of LOCAL_XXX definitions for Android NDK.
 
     These variable definitions will be used by Android NDK but do nothing for
     non-Android applications.
 
     Arguments:
@@ skipping 433 matching lines @@
     root_makefile.write("endif\n")
   root_makefile.write('\n')
 
   if (not generator_flags.get('standalone')
       and generator_flags.get('auto_regeneration', True)):
     WriteAutoRegenerationRule(params, root_makefile, makefile_name, build_files)
 
   root_makefile.write(SHARED_FOOTER)
 
   root_makefile.close()