Use $root:default as a "default" rule

When the root build file is changed in .gn file, we should check
$root:default rather than //:default when looking for "default" rule.

Review-Url: https://codereview.chromium.org/2824153002
Cr-Commit-Position: refs/heads/master@{#465758}

tools/gn/build_settings.cc

@@ -25,6 +25,10 @@ BuildSettings::BuildSettings(const BuildSettings& other)
 BuildSettings::~BuildSettings() {
 }
 
+void BuildSettings::SetRootTargetLabel(const Label& r) {
+  root_target_label_ = r;
+}
+
 void BuildSettings::SetRootPath(const base::FilePath& r) {
   DCHECK(r.value()[r.value().size() - 1] != base::FilePath::kSeparators[0]);
   root_path_ = r.NormalizePathSeparatorsTo('/');

tools/gn/build_settings.h

@@ -14,6 +14,7 @@
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "tools/gn/args.h"
+#include "tools/gn/label.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/source_dir.h"
 #include "tools/gn/source_file.h"
@@ -31,6 +32,10 @@ class BuildSettings {
   BuildSettings(const BuildSettings& other);
   ~BuildSettings();
 
+  // Root target label.
+  const Label& root_target_label() const { return root_target_label_; }
+  void SetRootTargetLabel(const Label& r);
+
   // Absolute path of the source root on the local system. Everything is
   // relative to this. Does not end in a [back]slash.
   const base::FilePath& root_path() const { return root_path_; }
@@ -104,6 +109,7 @@ class BuildSettings {
   }
 
  private:
+  Label root_target_label_;
   base::FilePath root_path_;
   std::string root_path_utf8_;
   base::FilePath secondary_source_path_;

tools/gn/docs/reference.md

@@ -5861,8 +5861,9 @@
   All generated targets (see "gn help execution") will be added to an implicit
   build rule called "all" so "ninja all" will always compile everything. The
   default rule will be used by Ninja if no specific target is specified (just
-  typing "ninja"). If there is a target named "//:default" it will be the
-  default build rule, otherwise the implicit "all" rule will be used.
+  typing "ninja"). If there is a target named "default" in the root build file,
+  it will be the default build rule, otherwise the implicit "all" rule will be
+  used.
 ```
 
 #### **Phony rules**

tools/gn/ninja_build_writer.cc

@@ -349,8 +349,9 @@ The "all" and "default" rules
   All generated targets (see "gn help execution") will be added to an implicit
   build rule called "all" so "ninja all" will always compile everything. The
   default rule will be used by Ninja if no specific target is specified (just
-  typing "ninja"). If there is a target named "//:default" it will be the
-  default build rule, otherwise the implicit "all" rule will be used.
+  typing "ninja"). If there is a target named "default" in the root build file,
+  it will be the default build rule, otherwise the implicit "all" rule will be
+  used.
 
 Phony rules
 
@@ -396,7 +397,7 @@ bool NinjaBuildWriter::WritePhonyAndAllRules(Err* err) {
   written_rules.insert("all");
 
   // Set if we encounter a target named "//:default".
-  bool default_target_exists = false;
+  const Target* default_target = nullptr;
 
   // Targets in the root build file.
   std::vector<const Target*> toplevel_targets;
@@ -418,8 +419,9 @@ bool NinjaBuildWriter::WritePhonyAndAllRules(Err* err) {
     const Label& label = target->label();
     const std::string& short_name = label.name();
 
-    if (label.dir().value() == "//" && label.name() == "default")
-      default_target_exists = true;
+    if (label.dir() == build_settings_->root_target_label().dir() &&
+        short_name == "default")
+      default_target = target;
 
     // Count the number of targets with the given short name.
     Counts& short_names_counts = short_names[short_name];
@@ -537,10 +539,18 @@ bool NinjaBuildWriter::WritePhonyAndAllRules(Err* err) {
   }
   out_ << std::endl;
 
-  if (default_target_exists)
-    out_ << "\ndefault default" << std::endl;
-  else if (!default_toolchain_targets_.empty())
+  if (default_target) {
+    // Use the short name when available
+    if (written_rules.find("default") != written_rules.end()) {
+      out_ << "\ndefault default" << std::endl;
+    } else {
+      out_ << "\ndefault ";
+      path_output_.WriteFile(out_, default_target->dependency_output_file());
+      out_ << std::endl;
+    }
+  } else if (!default_toolchain_targets_.empty()) {
     out_ << "\ndefault all" << std::endl;
+  }
 
   return true;
 }

tools/gn/setup.cc

@@ -698,6 +698,7 @@ bool Setup::RunConfigFile() {
 bool Setup::FillOtherConfig(const base::CommandLine& cmdline) {
   Err err;
   SourceDir current_dir("//");
+  Label root_target_label(current_dir, "");
 
   // Secondary source path, read from the config file if present.
   // Read from the config file if present.
@@ -720,8 +721,7 @@ bool Setup::FillOtherConfig(const base::CommandLine& cmdline) {
       return false;
     }
 
-    Label root_target_label =
-        Label::Resolve(current_dir, Label(), *root_value, &err);
+    root_target_label = Label::Resolve(current_dir, Label(), *root_value, &err);
     if (err.has_error()) {
       err.PrintToStdout();
       return false;
@@ -729,6 +729,7 @@ bool Setup::FillOtherConfig(const base::CommandLine& cmdline) {
 
     root_build_file_ = Loader::BuildFileForLabel(root_target_label);
   }
+  build_settings_.SetRootTargetLabel(root_target_label);
 
   // Build config file.
   const Value* build_config_value =