Use $root:default as a "default" rule

tools/gn/ninja_build_writer.cc

Index: tools/gn/ninja_build_writer.cc
diff --git a/tools/gn/ninja_build_writer.cc b/tools/gn/ninja_build_writer.cc
index 2f2336cde034b77baf63cfcc8963f195b51347b5..85e7e617865db27fa5d56f1edc62956684b6e240 100644
--- a/tools/gn/ninja_build_writer.cc
+++ b/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" (or $root:default in

[brettw, 2017/04/19 19:49:25]

Ditto

[Petr Hosek, 2017/04/19 20:20:26]

Done.

+  case the non-default root build target is used) 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 +539,21 @@ 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 {
+      EscapeOptions ninja_escape;
+      ninja_escape.mode = ESCAPE_NINJA;
+      std::string name = default_target->label().GetUserVisibleName(false);

[brettw, 2017/04/19 19:49:25]

This is making assumptions about the types of rules written. This should
reference the file associated with the target instead. This will be
default_target->dependency_output_file() and write with a PathOutput object.

[Petr Hosek, 2017/04/19 20:20:26]

Done.

+      base::TrimString(name, "/", &name);
+      std::string escaped = EscapeString(name, ninja_escape, nullptr);
+      out_ << "\ndefault " << escaped << std::endl;
+    }
+  } else if (!default_toolchain_targets_.empty()) {
     out_ << "\ndefault all" << std::endl;
+  }
 
   return true;
 }