GN: Use implicit dependency for binary input deps

tools/gn/ninja_binary_target_writer_unittest.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/ninja_binary_target_writer.h"
 
 #include <sstream>
 #include <utility>
 
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 276 matching lines @@
   const char expected[] =
       "defines =\n"
       "include_dirs =\n"
       "cflags =\n"
       "cflags_cc =\n"
       "root_out_dir = .\n"
       "target_out_dir = obj/foo\n"
       "target_output_name = libshlib\n"
       "\n"
       "build obj/foo/libshlib.input1.o: cxx ../../foo/input1.cc"
-        " || obj/foo/action.stamp\n"
+        " | obj/foo/action.stamp\n"

[brettw, 2016/06/16 19:41:34]

Actually, we specifically don't want to change this case. This is what
order-only deps were designed for.

What I was imagining when I talked about this is how the "inputs" list in a
binary target is treated. Currently they also appear in the order only deps, but
I think we want to split them out to be implicit deps. This should apply only to
the explicit inputs on a target, and not the transitive dependencies of it. So
it would apply to these things:

source_set("foo") {
  sources = [ "foo", "bar" ]
  inputs = [ "baz.dat" ]
}

Changing all actions to be implicit dependencies of binary targets that depend
on them in some way (what it looks like you're doing) will reduce build
parallelism significantly.

[Petr Hosek, 2016/06/16 23:11:47]

Acknowledged.

       "build obj/foo/libshlib.input2.o: cxx ../../foo/input2.cc"
-        " || obj/foo/action.stamp\n"
+        " | obj/foo/action.stamp\n"
       "\n"
       "build ./libshlib.so.6: solink obj/foo/libshlib.input1.o "
       // The order-only dependency here is stricly unnecessary since the
       // sources list this as an order-only dep. See discussion in the code
       // that writes this.
           "obj/foo/libshlib.input2.o || obj/foo/action.stamp\n"
       "  ldflags =\n"
       "  libs =\n"
       "  output_extension = .so.6\n"
       "  output_dir = foo\n";
@@ skipping 537 matching lines @@
 
   EXPECT_FALSE(scheduler.is_failed());
 
   std::ostringstream out;
   NinjaBinaryTargetWriter writer(&target, out);
   writer.Run();
 
   // Should have issued an error.
   EXPECT_TRUE(scheduler.is_failed());
 }