Require build directories exist for some GN commands.

Some GN commands just query the state of the build. They generally take the
build directory as a first argument. But this is easy to forget and GN will
auto-create these directories if they don't exist. So I end up with directories
named "base/*" because I was trying to list all targets in base but forgot the
build argument.

This patch requires that the build directory contain a build.ninja file for
the "querying" commands to prevent this case.

Review URL: https://codereview.chromium.org/558763002

Cr-Commit-Position: refs/heads/master@{#294071}

tools/gn/command_args.cc

@@ -115,7 +115,7 @@ void PrintArgHelp(const base::StringPiece& name, const Value& value) {
 int ListArgs(const std::string& build_dir) {
   Setup* setup = new Setup;
   setup->set_check_for_bad_items(false);
-  if (!setup->DoSetup(build_dir) || !setup->Run())
+  if (!setup->DoSetup(build_dir, false) || !setup->Run())
     return 1;
 
   Scope::KeyValueMap build_args;
@@ -233,7 +233,7 @@ int EditArgsFile(const std::string& build_dir) {
     // Don't fill build arguments. We're about to edit the file which supplies
     // these in the first place.
     setup.set_fill_arguments(false);
-    if (!setup.DoSetup(build_dir))
+    if (!setup.DoSetup(build_dir, true))
       return 1;
 
     // Ensure the file exists. Need to normalize path separators since on

tools/gn/command_check.cc

@@ -51,7 +51,7 @@ int RunCheck(const std::vector<std::string>& args) {
 
   // Deliberately leaked to avoid expensive process teardown.
   Setup* setup = new Setup();
-  if (!setup->DoSetup(args[0]))
+  if (!setup->DoSetup(args[0], false))
     return 1;
   if (!setup->Run())
     return 1;

tools/gn/command_desc.cc

@@ -579,7 +579,7 @@ int RunDesc(const std::vector<std::string>& args) {
 
   // Deliberately leaked to avoid expensive process teardown.
   Setup* setup = new Setup;
-  if (!setup->DoSetup(args[0]))
+  if (!setup->DoSetup(args[0], false))
     return 1;
   if (!setup->Run())
     return 1;

tools/gn/command_gen.cc

@@ -77,7 +77,7 @@ int RunGen(const std::vector<std::string>& args) {
 
   // Deliberately leaked to avoid expensive process teardown.
   Setup* setup = new Setup();
-  if (!setup->DoSetup(args[0]))
+  if (!setup->DoSetup(args[0], true))
     return 1;
 
   if (CommandLine::ForCurrentProcess()->HasSwitch(kSwitchCheck))

tools/gn/command_ls.cc

@@ -67,7 +67,7 @@ int RunLs(const std::vector<std::string>& args) {
   }
 
   Setup* setup = new Setup;
-  if (!setup->DoSetup(args[0]) || !setup->Run())
+  if (!setup->DoSetup(args[0], false) || !setup->Run())
     return 1;
 
   const CommandLine* cmdline = CommandLine::ForCurrentProcess();

tools/gn/command_refs.cc

@@ -230,7 +230,7 @@ int RunRefs(const std::vector<std::string>& args) {
 
   Setup* setup = new Setup;
   setup->set_check_for_bad_items(false);
-  if (!setup->DoSetup(args[0]) || !setup->Run())
+  if (!setup->DoSetup(args[0], false) || !setup->Run())
     return 1;
 
   // Figure out the target or targets that the user is querying.

tools/gn/setup.cc

@@ -225,7 +225,7 @@ Setup::Setup()
 Setup::~Setup() {
 }
 
-bool Setup::DoSetup(const std::string& build_dir) {
+bool Setup::DoSetup(const std::string& build_dir, bool force_create) {
   CommandLine* cmdline = CommandLine::ForCurrentProcess();
 
   scheduler_.set_verbose_logging(cmdline->HasSwitch(kSwitchVerbose));
@@ -241,8 +241,11 @@ bool Setup::DoSetup(const std::string& build_dir) {
     return false;
   if (!FillOtherConfig(*cmdline))
     return false;
-  if (!FillBuildDir(build_dir))  // Must be after FillSourceDir to resolve.
+
+  // Must be after FillSourceDir to resolve.
+  if (!FillBuildDir(build_dir, !force_create))
     return false;
+
   if (fill_arguments_) {
     if (!FillArguments(*cmdline))
       return false;
@@ -438,7 +441,7 @@ bool Setup::FillSourceDir(const CommandLine& cmdline) {
   return true;
 }
 
-bool Setup::FillBuildDir(const std::string& build_dir) {
+bool Setup::FillBuildDir(const std::string& build_dir, bool require_exists) {
   SourceDir resolved =
       SourceDirForCurrentDirectory(build_settings_.root_path()).
           ResolveRelativeDir(build_dir);
@@ -451,6 +454,21 @@ bool Setup::FillBuildDir(const std::string& build_dir) {
 
   if (scheduler_.verbose_logging())
     scheduler_.Log("Using build dir", resolved.value());
+
+  if (require_exists) {
+    base::FilePath build_dir_path = build_settings_.GetFullPath(resolved);
+    if (!base::PathExists(build_dir_path.Append(
+            FILE_PATH_LITERAL("build.ninja")))) {
+      Err(Location(), "Not a build directory.",
+          "This command requires an existing build directory. I interpreted "
+          "your input\n\"" + build_dir + "\" as:\n  " +
+          FilePathToUTF8(build_dir_path) +
+          "\nwhich doesn't seem to contain a previously-generated build.")
+          .PrintToStdout();
+      return false;
+    }
+  }
+
   build_settings_.SetBuildDir(resolved);
   return true;
 }

tools/gn/setup.h

@@ -98,7 +98,14 @@ class Setup : public CommonSetup {
   // The parameter is the string the user specified for the build directory. We
   // will try to interpret this as a SourceDir if possible, and will fail if is
   // is malformed.
-  bool DoSetup(const std::string& build_dir);
+  //
+  // With force_create = false, setup will fail if the build directory doesn't
+  // alreay exist with an args file in it. With force_create set to true, the
+  // directory will be created if necessary. Commands explicitly doing
+  // generation should set this to true to create it, but querying commands
+  // should set it to false to prevent creating oddly-named directories in case
+  // the user omits the build directory argument (which is easy to do).
+  bool DoSetup(const std::string& build_dir, bool force_create);
 
   // Runs the load, returning true on success. On failure, prints the error
   // and returns false. This includes both RunPreMessageLoop() and
@@ -139,8 +146,8 @@ class Setup : public CommonSetup {
 
   // Fills the build directory given the value the user has specified.
   // Must happen after FillSourceDir so we can resolve source-relative
-  // paths.
-  bool FillBuildDir(const std::string& build_dir);
+  // paths. If require_exists is false, it will fail if the dir doesn't exist.
+  bool FillBuildDir(const std::string& build_dir, bool require_exists);
 
   // Fills the python path portion of the command line. On failure, sets
   // it to just "python".