[M5+] add resolver::conan_probe

tests/conan_probe_live.cpp

@@ -0,0 +1,41 @@
+// Network-gated integration test for resolver::conan_probe.
+
+#include <catch2/catch_test_macros.hpp>
+
+import cargoxx.resolver;
+import cargoxx.util;
+import std;
+
+namespace {
+
+auto network_tests_enabled() -> bool {
+    auto* env = std::getenv("CARGOXX_NETWORK_TESTS");
+    return env != nullptr && std::string_view{env} == "1";
+}
+
+} // namespace
+
+TEST_CASE("conan_probe finds 'fmt' in conan-center-index",
+          "[resolver][network]") {
+    if (!network_tests_enabled()) {
+        SKIP("CARGOXX_NETWORK_TESTS != 1");
+    }
+    auto r = cargoxx::resolver::conan_probe("fmt");
+    REQUIRE(r.has_value());
+    REQUIRE_FALSE(r->find_package.empty());
+    REQUIRE_FALSE(r->targets.empty());
+    // fmt's recipe should set cmake_target_name = "fmt::fmt".
+    REQUIRE(r->targets.front() == "fmt::fmt");
+}
+
+TEST_CASE("conan_probe returns ResolutionUnknownPackage for a 404",
+          "[resolver][network]") {
+    if (!network_tests_enabled()) {
+        SKIP("CARGOXX_NETWORK_TESTS != 1");
+    }
+    auto r = cargoxx::resolver::conan_probe(
+        "definitely_not_a_real_pkg_cargoxx_xyzzy");
+    REQUIRE_FALSE(r.has_value());
+    REQUIRE(r.error().code ==
+            cargoxx::util::ErrorCode::ResolutionUnknownPackage);
+}