just build: add new option -p

... allowing to print the unique artifact built (if any). This
allows convenient inspection of the build result of targets that
define precisely one artifact.

3 files changed, 54 insertions, 4 deletions

diff --git a/src/buildtool/common/cli.hpp b/src/buildtool/common/cli.hpp
index 3c7ac45e..c6771cb3 100644
--- a/src/buildtool/common/cli.hpp
+++ b/src/buildtool/common/cli.hpp
@@ -114,6 +114,7 @@ struct BuildArguments {
     std::size_t build_jobs{};
     std::optional<std::string> dump_artifacts{std::nullopt};
     std::optional<std::string> print_to_stdout{std::nullopt};
+    bool print_unique{false};
     bool show_runfiles{false};
 };
 
@@ -533,6 +534,10 @@ static inline auto SetupExtendedBuildArguments(
                     clargs->print_to_stdout,
                     "After building, print the specified artifact to stdout.")
         ->type_name("LOGICAL_PATH");
+
+    app->add_flag("-p,--print-unique-artifact",
+                  clargs->print_unique,
+                  "Print the unique artifact, if any, to stdout.");
 }
 
 static inline auto SetupTCArguments(gsl::not_null<CLI::App*> const& app,
diff --git a/src/buildtool/computed_roots/evaluate.cpp b/src/buildtool/computed_roots/evaluate.cpp
index 6c05aadb..ed1df8de 100644
--- a/src/buildtool/computed_roots/evaluate.cpp
+++ b/src/buildtool/computed_roots/evaluate.cpp
@@ -317,6 +317,7 @@ void ComputeAndFill(
         StageArguments{.output_dir = root_dir, .remember = true};
     root_build_args.rebuild = std::nullopt;
     root_build_args.build.print_to_stdout = std::nullopt;
+    root_build_args.build.print_unique = false;
     root_build_args.build.dump_artifacts = std::nullopt;
     root_build_args.build.show_runfiles = false;
     auto root_exec_context = ExecutionContext{context->repo_config,
diff --git a/src/buildtool/graph_traverser/graph_traverser.hpp b/src/buildtool/graph_traverser/graph_traverser.hpp
index 51069c0b..3203f9c7 100644
--- a/src/buildtool/graph_traverser/graph_traverser.hpp
+++ b/src/buildtool/graph_traverser/graph_traverser.hpp
@@ -158,7 +158,13 @@ class GraphTraverser {
                          rel_paths,
                          artifact_nodes,
                          runfile_descriptions);
-            MaybePrintToStdout(rel_paths, artifact_nodes);
+            MaybePrintToStdout(
+                rel_paths,
+                artifact_nodes,
+                artifact_descriptions.size() == 1
+                    ? std::optional<std::string>{artifact_descriptions.begin()
+                                                     ->first}
+                    : std::nullopt);
             return BuildResult{.output_paths = std::move(rel_paths),
                                .extra_infos = std::move(infos),
                                .failed_artifacts = failed_artifacts};
@@ -182,7 +188,13 @@ class GraphTraverser {
                      artifact_nodes,
                      runfile_descriptions);
 
-        MaybePrintToStdout(rel_paths, artifact_nodes);
+        MaybePrintToStdout(
+            rel_paths,
+            artifact_nodes,
+            artifact_descriptions.size() == 1
+                ? std::optional<std::string>{artifact_descriptions.begin()
+                                                 ->first}
+                : std::nullopt);
 
         return BuildResult{.output_paths = *output_paths,
                            .extra_infos = std::move(infos),
@@ -671,8 +683,8 @@ class GraphTraverser {
 
     void MaybePrintToStdout(
         std::vector<std::filesystem::path> const& paths,
-        std::vector<DependencyGraph::ArtifactNode const*> const& artifacts)
-        const {
+        std::vector<DependencyGraph::ArtifactNode const*> const& artifacts,
+        std::optional<std::string> const& unique_artifact) const {
         if (clargs_.build.print_to_stdout) {
             auto const& remote = *context_.apis->remote;
             for (std::size_t i = 0; i < paths.size(); i++) {
@@ -751,6 +763,38 @@ class GraphTraverser {
                         "{} not a logical path of the specified target",
                         *(clargs_.build.print_to_stdout));
         }
+        else if (clargs_.build.print_unique) {
+            if (unique_artifact) {
+                auto const& remote = *context_.apis->remote;
+                std::optional<Artifact::ObjectInfo> info = std::nullopt;
+                for (std::size_t i = 0; i < paths.size(); i++) {
+                    if (paths[i] == unique_artifact) {
+                        info = artifacts[i]->Content().Info();
+                    }
+                }
+                if (info) {
+                    if (not remote.RetrieveToFds({*info},
+                                                 {dup(fileno(stdout))},
+                                                 /*raw_tree=*/false,
+                                                 &*context_.apis->local)) {
+                        Logger::Log(logger_,
+                                    LogLevel::Error,
+                                    "Failed to retrieve {}",
+                                    *unique_artifact);
+                    }
+                }
+                else {
+                    Logger::Log(logger_,
+                                LogLevel::Error,
+                                "Failed to obtain object information for {}",
+                                *unique_artifact);
+                }
+                return;
+            }
+            Logger::Log(logger_,
+                        LogLevel::Info,
+                        "Target does not have precisely one artifact.");
+        }
     }
 };