Add initial prototype for the GN meta-buildsystem.

tools/gn/label.cc

Index: tools/gn/label.cc
diff --git a/tools/gn/label.cc b/tools/gn/label.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f9b48da3c77eb54856cb80bd98d0714ea40119d2
--- /dev/null
+++ b/tools/gn/label.cc
@@ -0,0 +1,263 @@
+// 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/label.h"
+
+#include "base/logging.h"
+#include "tools/gn/err.h"
+#include "tools/gn/parse_tree.h"
+#include "tools/gn/value.h"
+
+namespace {
+
+// We print user visible label names with no trailing slash after the
+// directory name.
+std::string DirWithNoTrailingSlash(const SourceDir& dir) {
+  // Be careful not to trim if the input is just "/" or "//".
+  if (dir.value().size() > 2)
+    return dir.value().substr(0, dir.value().size() - 1);
+  return dir.value();
+}
+
+// Given the separate-out input (everything before the colon) in the dep rule,
+// computes the final build rule. Sets err on failure. On success,
+// |*used_implicit| will be set to whether the implicit current directory was
+// used. The value is used only for generating error messages.
+bool ComputeBuildLocationFromDep(const Value& input_value,
+                                 const SourceDir& current_dir,
+                                 const base::StringPiece& input,
+                                 SourceDir* result,
+                                 Err* err) {
+  // No rule, use the current locaton.
+  if (input.empty()) {
+    *result = current_dir;
+    return true;
+  }
+
+  // Don't allow directories to start with a single slash. All labels must be
+  // in the source root.
+  if (input[0] == '/' && (input.size() == 1 || input[1] != '/')) {
+    *err = Err(input_value, "Label can't start with a single slash",
+        "Labels must be either relative (no slash at the beginning) or be "
+        "absolute\ninside the source root (two slashes at the beginning).");
+    return false;
+  }
+
+  *result = current_dir.ResolveRelativeDir(input);
+  return true;
+}
+
+// Given the separated-out target name (after the colon) computes the final
+// name, using the implicit name from the previously-generated
+// computed_location if necessary. The input_value is used only for generating
+// error messages.
+bool ComputeTargetNameFromDep(const Value& input_value,
+                              const SourceDir& computed_location,
+                              const base::StringPiece& input,
+                              std::string* result,
+                              Err* err) {
+  if (!input.empty()) {
+    // Easy case: input is specified, just use it.
+    result->assign(input.data(), input.size());
+    return true;
+  }
+
+  const std::string& loc = computed_location.value();
+
+  // Use implicit name. The path will be "//", "//base/", "//base/i18n/", etc.
+  if (loc.size() <= 1) {
+    *err = Err(input_value, "This dependency name is empty");
+    return false;
+  }
+
+  size_t next_to_last_slash = loc.rfind('/', loc.size() - 2);
+  DCHECK(next_to_last_slash != std::string::npos);
+  result->assign(&loc[next_to_last_slash + 1],
+                 loc.size() - next_to_last_slash - 2);
+  return true;
+}
+
+// The original value is used only for error reporting, use the |input| as the
+// input to this function (which may be a substring of the original value when
+// we're parsing toolchains.
+//
+// If the output toolchain vars are NULL, then we'll report an error if we
+// find a toolchain specified (this is used when recursively parsing toolchain
+// labels which themselves can't have toolchain specs).
+//
+// We assume that the output variables are initialized to empty so we don't
+// write them unless we need them to contain something.
+//
+// Returns true on success. On failure, the out* variables might be written to
+// but shouldn't be used.
+bool Resolve(const SourceDir& current_dir,
+             const Label& current_toolchain,
+             const Value& original_value,
+             const base::StringPiece& input,
+             SourceDir* out_dir,
+             std::string* out_name,
+             SourceDir* out_toolchain_dir,
+             std::string* out_toolchain_name,
+             Err* err) {
+  // To workaround the problem that StringPiece operator[] doesn't return a ref.
+  const char* input_str = input.data();
+
+  size_t path_separator = input.find_first_of(":(");
+  base::StringPiece location_piece;
+  base::StringPiece name_piece;
+  base::StringPiece toolchain_piece;
+  if (path_separator == std::string::npos) {
+    location_piece = input;
+    // Leave name & toolchain piece null.
+  } else {
+    location_piece = base::StringPiece(&input_str[0], path_separator);
+
+    size_t toolchain_separator = input.find('(', path_separator);
+    if (toolchain_separator == std::string::npos) {
+      name_piece = base::StringPiece(&input_str[path_separator + 1],
+                                     input.size() - path_separator - 1);
+      // Leave location piece null.
+    } else if (!out_toolchain_dir) {
+      // Toolchain specified but not allows in this context.
+      *err = Err(original_value, "Toolchain has a toolchain.",
+          "Your toolchain definition (inside the parens) seems to itself "
+          "have a\ntoolchain. Don't do this.");
+      return false;
+    } else {
+      // Name piece is everything between the two separators. Note that the
+      // separators may be the same (e.g. "//foo(bar)" which means empty name.
+      if (toolchain_separator > path_separator) {
+        name_piece = base::StringPiece(
+            &input_str[path_separator + 1],
+            toolchain_separator - path_separator - 1);
+      }
+
+      // Toolchain name should end in a ) and this should be the end of the
+      // string.
+      if (input[input.size() - 1] != ')') {
+        *err = Err(original_value, "Bad toolchain name.",
+            "Toolchain name must end in a \")\" at the end of the label.");
+        return false;
+      }
+
+      // Subtract off the two parens to just get the toolchain name.
+      toolchain_piece = base::StringPiece(
+          &input_str[toolchain_separator + 1],
+          input.size() - toolchain_separator - 2);
+    }
+  }
+
+  // Everything before the separator is the filename.
+  // We allow three cases:
+  //   Absolute:                "//foo:bar" -> /foo:bar
+  //   Target in current file:  ":foo"     -> <currentdir>:foo
+  //   Path with implicit name: "/foo"     -> /foo:foo
+  if (location_piece.empty() && name_piece.empty()) {
+    // Can't use both implicit filename and name (":").
+    *err = Err(original_value, "This doesn't specify a dependency.");
+    return false;
+  }
+
+  if (!ComputeBuildLocationFromDep(original_value, current_dir, location_piece,
+                                   out_dir, err))
+    return false;
+
+  if (!ComputeTargetNameFromDep(original_value, *out_dir, name_piece,
+                                out_name, err))
+    return false;
+
+  // Last, do the toolchains.
+  if (out_toolchain_dir) {
+    // Handle empty toolchain strings. We don't allow normal labels to be
+    // empty so we can't allow the recursive call of this function to do this
+    // check.
+    if (toolchain_piece.empty()) {
+      *out_toolchain_dir = current_toolchain.dir();
+      *out_toolchain_name = current_toolchain.name();
+      return true;
+    } else {
+      return Resolve(current_dir, current_toolchain,
+                     original_value, toolchain_piece,
+                     out_toolchain_dir, out_toolchain_name, NULL, NULL, err);
+    }
+  }
+  return true;
+}
+
+}  // namespace
+
+Label::Label() {
+}
+
+Label::Label(const SourceDir& dir,
+             const base::StringPiece& name,
+             const SourceDir& toolchain_dir,
+             const base::StringPiece& toolchain_name)
+    : dir_(dir),
+      toolchain_dir_(toolchain_dir) {
+  name_.assign(name.data(), name.size());
+  toolchain_name_.assign(toolchain_name.data(), toolchain_name.size());
+}
+
+Label::~Label() {
+}
+
+// static
+Label Label::Resolve(const SourceDir& current_dir,
+                     const Label& current_toolchain,
+                     const Value& input,
+                     Err* err) {
+  Label ret;
+  if (input.type() != Value::STRING) {
+    *err = Err(input, "Dependency is not a string.");
+    return ret;
+  }
+  const std::string& input_string = input.string_value();
+  if (input_string.empty()) {
+    *err = Err(input, "Dependency string is empty.");
+    return ret;
+  }
+
+  if (!::Resolve(current_dir, current_toolchain, input, input_string,
+                 &ret.dir_, &ret.name_,
+                 &ret.toolchain_dir_, &ret.toolchain_name_,
+                 err))
+    return Label();
+  return ret;
+}
+
+Label Label::GetToolchainLabel() const {
+  return Label(toolchain_dir_, toolchain_name_,
+               SourceDir(), base::StringPiece());
+}
+
+std::string Label::GetUserVisibleName(bool include_toolchain) const {
+  std::string ret;
+  ret.reserve(dir_.value().size() + name_.size() + 1);
+
+  if (dir_.is_null())
+    return ret;
+
+  ret = DirWithNoTrailingSlash(dir_);
+  ret.push_back(':');
+  ret.append(name_);
+
+  if (include_toolchain) {
+    ret.push_back('(');
+    if (!toolchain_dir_.is_null() && !toolchain_name_.empty()) {
+      ret.append(DirWithNoTrailingSlash(toolchain_dir_));
+      ret.push_back(':');
+      ret.append(toolchain_name_);
+    }
+    ret.push_back(')');
+  }
+  return ret;
+}
+
+std::string Label::GetUserVisibleName(const Label& default_toolchain) const {
+  bool include_toolchain =
+      default_toolchain.dir() != toolchain_dir_ ||
+      default_toolchain.name() != toolchain_name_;
+  return GetUserVisibleName(include_toolchain);
+}