blob: 6914962d3a21f3df6d25c43e9ca5858a83b4f7ad [file] [log] [blame]
// 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 "gn/label.h"
#include "base/logging.h"
#include "base/strings/string_util.h"
#include "gn/err.h"
#include "gn/filesystem_utils.h"
#include "gn/parse_tree.h"
#include "gn/value.h"
#include "util/build_config.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,
std::string_view source_root,
std::string_view input,
SourceDir* result,
Err* err) {
// No rule, use the current location.
if (input.empty()) {
*result = current_dir;
return true;
*result =
current_dir.ResolveRelativeDir(input_value, input, err, source_root);
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,
std::string_view input,
StringAtom* result,
Err* err) {
if (!input.empty()) {
// Easy case: input is specified, just use it.
*result = StringAtom(input);
return true;
const std::string& loc = computed_location.value();
// Use implicit name. The path will be "//", "//base/", "//base/i18n/", etc.
if (loc.size() <= 2) {
*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 = StringAtom(std::string_view{&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,
std::string_view source_root,
const Label& current_toolchain,
const Value& original_value,
std::string_view input,
SourceDir* out_dir,
StringAtom* out_name,
SourceDir* out_toolchain_dir,
StringAtom* out_toolchain_name,
Err* err) {
// To workaround the problem that std::string_view operator[] doesn't return a
// ref.
const char* input_str =;
size_t offset = 0;
#if defined(OS_WIN)
if (IsPathAbsolute(input)) {
size_t drive_letter_pos = input[0] == '/' ? 1 : 0;
if (input.size() > drive_letter_pos + 2 &&
input[drive_letter_pos + 1] == ':' &&
IsSlash(input[drive_letter_pos + 2]) &&
base::IsAsciiAlpha(input[drive_letter_pos])) {
// Skip over the drive letter colon.
offset = drive_letter_pos + 2;
size_t path_separator = input.find_first_of(":(", offset);
std::string_view location_piece;
std::string_view name_piece;
std::string_view toolchain_piece;
if (path_separator == std::string::npos) {
location_piece = input;
// Leave name & toolchain piece null.
} else {
location_piece = std::string_view(&input_str[0], path_separator);
size_t toolchain_separator = input.find('(', path_separator);
if (toolchain_separator == std::string::npos) {
name_piece = std::string_view(&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 = std::string_view(&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 =
std::string_view(&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, source_root,
location_piece, out_dir, err))
return false;
if (!ComputeTargetNameFromDep(original_value, *out_dir, name_piece, out_name,
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_atom();
return true;
} else {
return Resolve(current_dir, source_root, current_toolchain,
original_value, toolchain_piece, out_toolchain_dir,
out_toolchain_name, nullptr, nullptr, err);
return true;
} // namespace
const char kLabels_Help[] =
R"*(About labels
Everything that can participate in the dependency graph (targets, configs,
and toolchains) are identified by labels. A common label looks like:
This consists of a source-root-absolute path, a colon, and a name. This means
to look for the thing named "test_support" in "base/test/".
You can also specify system absolute paths if necessary. Typically such
paths would be specified via a build arg so the developer can specify where
the component is on their system.
/usr/local/foo:bar (Posix)
/C:/Program Files/MyLibs:bar (Windows)
A canonical label includes the label of the toolchain being used. Normally,
the toolchain label is implicitly inherited from the current execution
context, but you can override this to specify cross-toolchain dependencies:
Here GN will look for the toolchain definition called "msvc" in the file
"//build/toolchain/win" to know how to compile this target.
Relative labels
If you want to refer to something in the same buildfile, you can omit
the path name and just start with a colon. This format is recommended for
all same-file references.
Labels can be specified as being relative to the current directory.
Stylistically, we prefer to use absolute paths for all non-file-local
references unless a build file needs to be run in different contexts (like a
project needs to be both standalone and pulled into other projects in
difference places in the directory hierarchy).
Implicit names
If a name is unspecified, it will inherit the directory name. Stylistically,
we prefer to omit the colon and name when possible:
//net -> //net:net
//tools/gn -> //tools/gn:gn
Label::Label() : hash_(ComputeHash()) {}
Label::Label(const SourceDir& dir,
std::string_view name,
const SourceDir& toolchain_dir,
std::string_view toolchain_name)
: dir_(dir),
hash_(ComputeHash()) {}
Label::Label(const SourceDir& dir, std::string_view name)
: dir_(dir), name_(StringAtom(name)), hash_(ComputeHash()) {}
// static
Label Label::Resolve(const SourceDir& current_dir,
std::string_view source_root,
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, source_root, current_toolchain, input,
input_string, &ret.dir_, &ret.name_, &ret.toolchain_dir_,
&ret.toolchain_name_, err))
return Label();
ret.hash_ = ret.ComputeHash();
return ret;
Label Label::GetToolchainLabel() const {
return Label(toolchain_dir_, toolchain_name_);
Label Label::GetWithNoToolchain() const {
return Label(dir_, name_);
std::string Label::GetUserVisibleName(bool include_toolchain) const {
std::string ret;
ret.reserve(dir_.value().size() + name_.str().size() + 1);
if (dir_.is_null())
return ret;
ret = DirWithNoTrailingSlash(dir_);
if (include_toolchain) {
if (!toolchain_dir_.is_null() && !toolchain_name_.empty()) {
return ret;
std::string Label::GetUserVisibleName(const Label& default_toolchain) const {
bool include_toolchain = default_toolchain.dir() != toolchain_dir_ ||
default_toolchain.name_atom() != toolchain_name_;
return GetUserVisibleName(include_toolchain);