Make the gn copy() tool honor dependencies.

Previously it didn't, and perhaps there was no need for
it to, but it seems like NaCl has a need. Specifically,
NaCl has two targets A and B with both run fine on their
own, but A can delete the output of B, and so needs to run
before B.

R=brettw@chromium.org
BUG=428576

Review URL: https://codereview.chromium.org/693443002

Cr-Commit-Position: refs/heads/master@{#302342}

tools/gn/ninja_copy_target_writer.cc

@@ -71,6 +71,9 @@ void NinjaCopyTargetWriter::WriteCopyRules(
       GetNinjaRulePrefixForToolchain(settings_) +
       Toolchain::ToolTypeToName(Toolchain::TYPE_COPY);
 
+  OutputFile input_dep =
+      WriteInputDepsStampAndGetDep(std::vector<const Target*>());
+
   // Note that we don't write implicit deps for copy steps. "copy" only
   // depends on the output files themselves, rather than having includes
   // (the possibility of generated #includes is the main reason for implicit
@@ -92,6 +95,11 @@ void NinjaCopyTargetWriter::WriteCopyRules(
   //
   // Moreover, doing this assumes that the copy step is always a simple
   // locally run command, so there is no need for a toolchain dependency.
+  //
+  // Note that there is the need in some cases for order-only dependencies
+  // where a command might need to make sure something else runs before it runs
+  // to avoid conflicts. Such cases should be avoided where possible, but
+  // sometimes that's not possible.
   for (size_t i = 0; i < target_->sources().size(); i++) {
     const SourceFile& input_file = target_->sources()[i];
 
@@ -104,6 +112,10 @@ void NinjaCopyTargetWriter::WriteCopyRules(
     path_output_.WriteFile(out_, output_file);
     out_ << ": " << tool_name << " ";
     path_output_.WriteFile(out_, input_file);
+    if (!input_dep.value().empty()) {
+      out_ << " || ";
+      path_output_.WriteFile(out_, input_dep);
+    }
     out_ << std::endl;
   }
 }

tools/gn/ninja_copy_target_writer_unittest.cc

@@ -10,7 +10,7 @@
 #include "tools/gn/target.h"
 #include "tools/gn/test_with_scope.h"
 
-// Tests mutliple files with an output pattern and no toolchain dependency.
+// Tests multiple files with an output pattern and no toolchain dependency.
 TEST(NinjaCopyTargetWriter, Run) {
   TestWithScope setup;
   Err err;
@@ -71,3 +71,33 @@ TEST(NinjaCopyTargetWriter, ToolchainDeps) {
   std::string out_str = out.str();
   EXPECT_EQ(expected_linux, out_str);
 }
+
+TEST(NinjaCopyTargetWriter, OrderOnlyDeps) {
+  TestWithScope setup;
+  Err err;
+
+  setup.settings()->set_target_os(Settings::LINUX);
+  setup.build_settings()->SetBuildDir(SourceDir("//out/Debug/"));
+
+  Target target(setup.settings(), Label(SourceDir("//foo/"), "bar"));
+  target.set_output_type(Target::COPY_FILES);
+  target.sources().push_back(SourceFile("//foo/input1.txt"));
+  target.action_values().outputs() =
+      SubstitutionList::MakeForTest("//out/Debug/{{source_name_part}}.out");
+  target.inputs().push_back(SourceFile("//foo/script.py"));
+  target.SetToolchain(setup.toolchain());
+  ASSERT_TRUE(target.OnResolved(&err));
+
+  std::ostringstream out;
+  NinjaCopyTargetWriter writer(&target, out);
+  writer.Run();
+
+  const char expected_linux[] =
+      "build obj/foo/bar.inputdeps.stamp: stamp ../../foo/script.py\n"
+      "build input1.out: copy ../../foo/input1.txt || "
+          "obj/foo/bar.inputdeps.stamp\n"
+      "\n"
+      "build obj/foo/bar.stamp: stamp input1.out\n";
+  std::string out_str = out.str();
+  EXPECT_EQ(expected_linux, out_str);
+}