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// Copyright 2018 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/metadata.h"
#include "gn/filesystem_utils.h"
const char kMetadata_Help[] =
R"(Metadata Collection
Metadata is information attached to targets throughout the dependency tree. GN
allows for the collection of this data into files written during the generation
step, enabling users to expose and aggregate this data based on the dependency
tree.
generated_file targets
Similar to the write_file() function, the generated_file target type
creates a file in the specified location with the specified content. The
primary difference between write_file() and this target type is that the
write_file function does the file write at parse time, while the
generated_file target type writes at target resolution time. See
"gn help generated_file" for more detail.
When written at target resolution time, generated_file enables GN to
collect and write aggregated metadata from dependents.
A generated_file target can declare either 'contents' to write statically
known contents to a file or 'data_keys' to aggregate metadata and write the
result to a file. It can also specify 'walk_keys' (to restrict the metadata
collection), 'output_conversion', and 'rebase'.
Collection and Aggregation
Targets can declare a 'metadata' variable containing a scope, and this
metadata may be collected and written out to a file specified by
generated_file aggregation targets. The 'metadata' scope must contain
only list values since the aggregation step collects a list of these values.
During the target resolution, generated_file targets will walk their
dependencies recursively, collecting metadata based on the specified
'data_keys'. 'data_keys' is specified as a list of strings, used by the walk
to identify which variables in dependencies' 'metadata' scopes to collect.
The walk begins with the listed dependencies of the 'generated_file' target.
The 'metadata' scope for each dependency is inspected for matching elements
of the 'generated_file' target's 'data_keys' list. If a match is found, the
data from the dependent's matching key list is appended to the aggregate walk
list. Note that this means that if more than one walk key is specified, the
data in all of them will be aggregated into one list. From there, the walk
will then recurse into the dependencies of each target it encounters,
collecting the specified metadata for each.
For example:
group("a") {
metadata = {
doom_melon = [ "enable" ]
my_files = [ "foo.cpp" ]
my_extra_files = [ "bar.cpp" ]
}
deps = [ ":b" ]
}
group("b") {
metadata = {
my_files = [ "baz.cpp" ]
}
}
generated_file("metadata") {
outputs = [ "$root_build_dir/my_files.json" ]
data_keys = [ "my_files", "my_extra_files" ]
deps = [ ":a" ]
}
The above will produce the following file data:
foo.cpp
bar.cpp
baz.cpp
The dependency walk can be limited by using the 'walk_keys'. This is a list of
labels that should be included in the walk. All labels specified here should
also be in one of the deps lists. These keys act as barriers, where the walk
will only recurse into the targets listed. An empty list in all specified
barriers will end that portion of the walk.
group("a") {
metadata = {
my_files = [ "foo.cpp" ]
my_files_barrier = [ ":b" ]
}
deps = [ ":b", ":c" ]
}
group("b") {
metadata = {
my_files = [ "bar.cpp" ]
}
}
group("c") {
metadata = {
my_files = [ "doom_melon.cpp" ]
}
}
generated_file("metadata") {
outputs = [ "$root_build_dir/my_files.json" ]
data_keys = [ "my_files" ]
walk_keys = [ "my_files_barrier" ]
deps = [ ":a" ]
}
The above will produce the following file data (note that `doom_melon.cpp` is
not included):
foo.cpp
bar.cpp
A common example of this sort of barrier is in builds that have host tools
built as part of the tree, but do not want the metadata from those host tools
to be collected with the target-side code.
Common Uses
Metadata can be used to collect information about the different targets in the
build, and so a common use is to provide post-build tooling with a set of data
necessary to do aggregation tasks. For example, if each test target specifies
the output location of its binary to run in a metadata field, that can be
collected into a single file listing the locations of all tests in the
dependency tree. A local build tool (or continuous integration infrastructure)
can then use that file to know which tests exist, and where, and run them
accordingly.
Another use is in image creation, where a post-build image tool needs to know
various pieces of information about the components it should include in order
to put together the correct image.
)";
bool Metadata::WalkStep(const BuildSettings* settings,
const std::vector<std::string>& keys_to_extract,
const std::vector<std::string>& keys_to_walk,
const SourceDir& rebase_dir,
std::vector<Value>* next_walk_keys,
std::vector<Value>* result,
Err* err) const {
// If there's no metadata, there's nothing to find, so quick exit.
if (contents_.empty()) {
next_walk_keys->emplace_back(nullptr, "");
return true;
}
// Pull the data from each specified key.
for (const auto& key : keys_to_extract) {
auto iter = contents_.find(key);
if (iter == contents_.end())
continue;
assert(iter->second.type() == Value::LIST);
if (!rebase_dir.is_null()) {
for (const auto& val : iter->second.list_value()) {
std::pair<Value, bool> pair =
this->RebaseValue(settings, rebase_dir, val, err);
if (!pair.second)
return false;
result->push_back(pair.first);
}
} else {
result->insert(result->end(), iter->second.list_value().begin(),
iter->second.list_value().end());
}
}
// Get the targets to look at next. If no keys_to_walk are present, we push
// the empty string to the list so that the target knows to include its deps
// and data_deps. The values used here must be lists of strings.
bool found_walk_key = false;
for (const auto& key : keys_to_walk) {
auto iter = contents_.find(key);
if (iter != contents_.end()) {
found_walk_key = true;
assert(iter->second.type() == Value::LIST);
for (const auto& val : iter->second.list_value()) {
if (!val.VerifyTypeIs(Value::STRING, err))
return false;
next_walk_keys->emplace_back(val);
}
}
}
if (!found_walk_key)
next_walk_keys->emplace_back(nullptr, "");
return true;
}
std::pair<Value, bool> Metadata::RebaseValue(const BuildSettings* settings,
const SourceDir& rebase_dir,
const Value& value,
Err* err) const {
switch (value.type()) {
case Value::STRING:
return this->RebaseStringValue(settings, rebase_dir, value, err);
case Value::LIST:
return this->RebaseListValue(settings, rebase_dir, value, err);
case Value::SCOPE:
return this->RebaseScopeValue(settings, rebase_dir, value, err);
default:
return std::make_pair(value, true);
}
}
std::pair<Value, bool> Metadata::RebaseStringValue(
const BuildSettings* settings,
const SourceDir& rebase_dir,
const Value& value,
Err* err) const {
if (!value.VerifyTypeIs(Value::STRING, err))
return std::make_pair(value, false);
std::string filename = source_dir_.ResolveRelativeAs(
/*as_file = */ true, value, err, settings->root_path_utf8());
if (err->has_error())
return std::make_pair(value, false);
Value rebased_value(value.origin(), RebasePath(filename, rebase_dir,
settings->root_path_utf8()));
return std::make_pair(rebased_value, true);
}
std::pair<Value, bool> Metadata::RebaseListValue(const BuildSettings* settings,
const SourceDir& rebase_dir,
const Value& value,
Err* err) const {
if (!value.VerifyTypeIs(Value::LIST, err))
return std::make_pair(value, false);
Value rebased_list_value(value.origin(), Value::LIST);
for (auto& val : value.list_value()) {
std::pair<Value, bool> pair = RebaseValue(settings, rebase_dir, val, err);
if (!pair.second)
return std::make_pair(value, false);
rebased_list_value.list_value().push_back(pair.first);
}
return std::make_pair(rebased_list_value, true);
}
std::pair<Value, bool> Metadata::RebaseScopeValue(const BuildSettings* settings,
const SourceDir& rebase_dir,
const Value& value,
Err* err) const {
if (!value.VerifyTypeIs(Value::SCOPE, err))
return std::make_pair(value, false);
Value rebased_scope_value(value);
Scope::KeyValueMap scope_values;
value.scope_value()->GetCurrentScopeValues(&scope_values);
for (auto& value_pair : scope_values) {
std::pair<Value, bool> pair =
RebaseValue(settings, rebase_dir, value_pair.second, err);
if (!pair.second)
return std::make_pair(value, false);
rebased_scope_value.scope_value()->SetValue(value_pair.first, pair.first,
value.origin());
}
return std::make_pair(rebased_scope_value, true);
}