[M6] cmd_build auto-resolves missing deps via resolver chain

src/cli/cmd_build.cpp

@@ -8,6 +8,7 @@ import cargoxx.linkdb;
 import cargoxx.lockfile;
 import cargoxx.codegen;
 import cargoxx.exec;
+import cargoxx.resolver;
 
 namespace cargoxx::cli {
 
@@ -146,17 +147,46 @@ auto cmd_build(const fs::path& project_root, bool no_build, bool release,
         return std::unexpected(layout_result.error());
     }
 
-    auto db = linkdb::Database::open(std::move(overlay_path));
+    const auto effective_overlay = overlay_path.value_or(linkdb::default_overlay_path());
+    auto db = linkdb::Database::open(effective_overlay);
     if (!db) {
         return std::unexpected(db.error());
     }
 
+    auto auto_resolve = [&](const std::string& name, const std::string& version,
+                             const std::vector<std::string>& components)
+        -> util::Result<void> {
+        auto build_fn = [&](const fs::path& root) {
+            return cmd_build(root, /*no_build=*/false, /*release=*/false,
+                              /*target=*/std::nullopt, effective_overlay);
+        };
+        const auto scratch_root =
+            std::filesystem::temp_directory_path() /
+            std::format("cargoxx-discover-{}", std::random_device{}());
+        auto disc = resolver::discover(name, version, components,
+                                        effective_overlay, scratch_root, build_fn);
+        std::error_code ec;
+        std::filesystem::remove_all(scratch_root, ec);
+        if (!disc) {
+            return std::unexpected(disc.error());
+        }
+        return {};
+    };
+
     auto resolve_list = [&](const std::vector<manifest::Dependency>& deps)
         -> util::Result<std::vector<linkdb::Recipe>> {
         std::vector<linkdb::Recipe> out;
         out.reserve(deps.size());
         for (const auto& dep : deps) {
             auto r = db->resolve(dep.name, dep.version_spec, dep.components);
+            if (!r && r.error().code == util::ErrorCode::LinkdbUnknownPackage) {
+                if (auto resolved = auto_resolve(dep.name, dep.version_spec,
+                                                  dep.components);
+                    !resolved) {
+                    return std::unexpected(resolved.error());
+                }
+                r = db->resolve(dep.name, dep.version_spec, dep.components);
+            }
             if (!r) {
                 return std::unexpected(r.error());
             }

tests/cmd_build.cpp

@@ -156,7 +156,7 @@ TEST_CASE("cmd_build fails for an unknown dep", "[cli][build]") {
 
     auto r = cmd_build(root, true, false, std::nullopt, overlay_path(parent));
     REQUIRE_FALSE(r.has_value());
-    REQUIRE(r.error().code == ErrorCode::LinkdbUnknownPackage);
+    REQUIRE(r.error().code == ErrorCode::ResolutionUnknownPackage);
 }
 
 TEST_CASE("cmd_build --release writes a release-typed build/CMakeLists",