[M5+] add resolver::conan_probe

CHANGELOG.md

@@ -78,6 +78,19 @@ All notable changes to cargoxx will be documented in this file.
   and `[build]` honoring `warnings_as_errors` and `sanitizers`. Source
   paths emitted relative to `build/` (i.e. prefixed with `../`).
   Output is deterministic. `tests/codegen_cmake.cpp` covers 11 cases.
+- `cargoxx.resolver::conan_probe(name)` — fetches
+  `https://raw.githubusercontent.com/conan-io/conan-center-index/master/recipes/<name>/all/conanfile.py`
+  via `curl` (text-only — never executes Python, per `SPEC.md` §14)
+  and feeds it through `parse_conanfile`. Pure parser handles both the
+  modern `set_property("cmake_target_name", "...")` form and the legacy
+  `names["cmake_find_package"] = "..."` form, derives the missing field
+  from the other when only one is set, normalizes bare names into the
+  canonical `<file>::<target>` shape, and substitutes Python f-string
+  `{...}` placeholders with the cmake_file_name so recipes like fmt's
+  `f"fmt::{target}"` parse correctly. `tests/conan_probe_parse.cpp`
+  covers 6 cases; `tests/conan_probe_live.cpp` (gated by
+  `CARGOXX_NETWORK_TESTS=1`) verifies fmt and a 404 path against the
+  real conan-center-index.
 - `cargoxx.resolver::nix_cmake_scan(store_path, package_name)` — walks
   `<store_path>/lib/cmake/**` for `*Config.cmake` / `*-config.cmake`
   files, scans them and their sibling `.cmake` files (e.g. the

CMakeLists.txt

@@ -54,6 +54,7 @@ target_sources(cargoxx
         src/exec/subprocess.cpp
         src/resolver/nixpkgs_probe.cpp
         src/resolver/nix_cmake_scan.cpp
+        src/resolver/conan_probe.cpp
         src/cli/cmd_new.cpp
         src/cli/cmd_build.cpp
         src/cli/cmd_run.cpp

docs/auto-resolution.md

@@ -193,8 +193,8 @@ auto verify_link(const Recipe& candidate,
 | Phase | Status | Commit |
 | --- | --- | --- |
 | 1. nixpkgs_probe + JSON parser | ✅ | `1c7ff39` |
-| 2. nix_cmake_scan | pending | — |
-| 3. conan_probe + parse_conanfile | pending | — |
+| 2. nix_cmake_scan | ✅ | `e63ac69` |
+| 3. conan_probe + parse_conanfile | ✅ | (this commit) |
 | 4. vcpkg_probe + parse_vcpkg_usage | pending | — |
 | 5. verify_link (tmp project + cmd_build) | pending | — |
 | 6. Database::discover + cmd_add wire-up + failure caching | pending | — |

src/resolver/conan_probe.cpp

@@ -0,0 +1,192 @@
+module cargoxx.resolver;
+
+import std;
+import cargoxx.util;
+import cargoxx.exec;
+
+namespace cargoxx::resolver {
+
+namespace {
+
+auto error(util::ErrorCode code, std::string msg) -> util::Error {
+    return util::Error{code, std::move(msg), "", std::nullopt, std::nullopt};
+}
+
+// Find the *value* (in quotes) of a key in patterns like
+//   set_property("cmake_target_name", "fmt::fmt")
+//   names["cmake_find_package"] = "fmt"
+//
+// `key_pattern` is a substring guaranteed to appear right before the value
+// (with quotes/punctuation between). We then look for the next quoted
+// string after `key_pattern`'s position.
+auto extract_quoted_after(std::string_view text, std::string_view key_pattern)
+    -> std::optional<std::string> {
+    auto pos = text.find(key_pattern);
+    if (pos == std::string_view::npos) {
+        return std::nullopt;
+    }
+    pos += key_pattern.size();
+    // Scan forward looking for the *next* quoted string.
+    while (pos < text.size()) {
+        char c = text[pos];
+        if (c == '"' || c == '\'') {
+            char quote = c;
+            ++pos;
+            std::string out;
+            while (pos < text.size() && text[pos] != quote) {
+                out += text[pos++];
+            }
+            if (pos < text.size()) {
+                return out;
+            }
+            return std::nullopt;
+        }
+        // newline → bail; the value is on this line per Conan convention
+        if (c == '\n') {
+            return std::nullopt;
+        }
+        ++pos;
+    }
+    return std::nullopt;
+}
+
+auto extract_set_property(std::string_view text, std::string_view property_name)
+    -> std::optional<std::string> {
+    auto needle = std::format("set_property(\"{}\"", property_name);
+    auto v = extract_quoted_after(text, needle);
+    if (v) {
+        return v;
+    }
+    needle = std::format("set_property('{}'", property_name);
+    return extract_quoted_after(text, needle);
+}
+
+auto extract_names_legacy(std::string_view text, std::string_view legacy_key)
+    -> std::optional<std::string> {
+    auto needle = std::format("names[\"{}\"]", legacy_key);
+    auto v = extract_quoted_after(text, needle);
+    if (v) {
+        return v;
+    }
+    needle = std::format("names['{}']", legacy_key);
+    return extract_quoted_after(text, needle);
+}
+
+} // namespace
+
+auto parse_conanfile(std::string_view text, const std::string& fallback_name)
+    -> util::Result<ConanRecipe> {
+    auto target = extract_set_property(text, "cmake_target_name");
+    auto file = extract_set_property(text, "cmake_file_name");
+
+    if (!target) {
+        target = extract_names_legacy(text, "cmake_find_package");
+    }
+    if (!file) {
+        file = extract_names_legacy(text, "cmake_find_package");
+    }
+
+    // If only one of the two surfaces, derive the other heuristically:
+    //   cmake_target_name "fmt::fmt"  → cmake_file_name "fmt"
+    //   cmake_file_name   "fmt"       → cmake_target_name "fmt::fmt"
+    if (target && !file) {
+        auto t = *target;
+        if (auto cc = t.find("::"); cc != std::string::npos) {
+            file = t.substr(0, cc);
+        } else {
+            file = t;
+        }
+    }
+    if (file && !target) {
+        target = std::format("{}::{}", *file, *file);
+    }
+
+    if (!target || !file) {
+        // Last resort: fall back to the package name itself.
+        if (!fallback_name.empty()) {
+            file = fallback_name;
+            target = std::format("{}::{}", fallback_name, fallback_name);
+        } else {
+            return std::unexpected(error(
+                util::ErrorCode::ResolutionUnknownPackage,
+                "conanfile.py contained no cmake_target_name or cmake_file_name"));
+        }
+    }
+
+    // Conan recipes often parameterize the target via Python f-strings:
+    //   f"fmt::{target}"  or  f"{name}::{component}"
+    // We can't evaluate Python — substitute every `{...}` placeholder with
+    // the cmake_file_name (or fallback) which is the canonical target stem
+    // for the vast majority of recipes.
+    auto substitute_braces = [&](std::string s) -> std::string {
+        const auto& sub = !file->empty() ? *file : fallback_name;
+        std::string out;
+        out.reserve(s.size());
+        std::size_t i = 0;
+        while (i < s.size()) {
+            if (s[i] == '{') {
+                auto close = s.find('}', i + 1);
+                if (close == std::string::npos) {
+                    out += s.substr(i);
+                    break;
+                }
+                out += sub;
+                i = close + 1;
+            } else {
+                out += s[i++];
+            }
+        }
+        return out;
+    };
+    *target = substitute_braces(*target);
+    *file = substitute_braces(*file);
+
+    // Normalize bare names to the conventional `<file>::<target>` form so
+    // `target_link_libraries` actually resolves. Legacy Conan recipes set
+    // `names["cmake_find_package"] = "spdlog"` for both fields, leaving us
+    // with a bare "spdlog" target that CMake won't accept as an imported
+    // target reference.
+    if (target->find("::") == std::string::npos) {
+        target = std::format("{}::{}", *file, *target);
+    }
+
+    return ConanRecipe{
+        .find_package = std::format("{} CONFIG REQUIRED", *file),
+        .targets = {*target},
+    };
+}
+
+auto conan_probe(const std::string& name) -> util::Result<ConanRecipe> {
+    if (name.empty()) {
+        return std::unexpected(error(util::ErrorCode::ResolutionUnknownPackage,
+                                     "package name is empty"));
+    }
+    auto url = std::format(
+        "https://raw.githubusercontent.com/conan-io/conan-center-index/"
+        "master/recipes/{}/all/conanfile.py",
+        name);
+    auto r = exec::run("curl", {"-fsSL", "--max-time", "30", url},
+                       exec::ExecOptions{
+                           .cwd = {},
+                           .env_overrides = {},
+                           .timeout = std::chrono::seconds{40},
+                           .inherit_stdio = false,
+                       });
+    if (!r) {
+        return std::unexpected(r.error());
+    }
+    if (r->exit_code == 22) {
+        // curl --fail returns 22 on HTTP 4xx — treat 404s as "not in conan".
+        return std::unexpected(error(util::ErrorCode::ResolutionUnknownPackage,
+                                     std::format("conan-center has no recipe for '{}'",
+                                                 name)));
+    }
+    if (r->exit_code != 0) {
+        return std::unexpected(error(
+            util::ErrorCode::ResolutionNetworkError,
+            std::format("curl failed (exit {}): {}", r->exit_code, r->stderr_text)));
+    }
+    return parse_conanfile(r->stdout_text, name);
+}
+
+} // namespace cargoxx::resolver

src/resolver/resolver.cppm

@@ -51,4 +51,24 @@ auto nix_cmake_scan(const std::filesystem::path& store_path,
                     const std::string& package_name)
     -> util::Result<NixCmakeCandidate>;
 
+// Output of a conan-center-index recipe scrape.
+struct ConanRecipe {
+    std::string find_package; // e.g. "fmt CONFIG REQUIRED"
+    std::vector<std::string> targets; // e.g. ["fmt::fmt"]
+};
+
+// Pure: scrapes a conanfile.py text for `cmake_target_name` and
+// `cmake_file_name`. Handles both the modern
+// `cpp_info.set_property("cmake_target_name", "...")` form and the
+// legacy `cpp_info.names["cmake_find_package"] = "..."` form. Returns
+// ResolutionUnknownPackage when no recognizable recipe is found.
+auto parse_conanfile(std::string_view conanfile_text, const std::string& fallback_name)
+    -> util::Result<ConanRecipe>;
+
+// Fetches https://raw.githubusercontent.com/conan-io/conan-center-index/
+// master/recipes/<name>/all/conanfile.py via `curl` and feeds it through
+// parse_conanfile. 404 → ResolutionUnknownPackage; transport errors →
+// ResolutionNetworkError.
+auto conan_probe(const std::string& name) -> util::Result<ConanRecipe>;
+
 } // namespace cargoxx::resolver

tests/CMakeLists.txt

@@ -28,3 +28,5 @@ cargoxx_add_test(nixpkgs_probe_parse)
 cargoxx_add_test(nixpkgs_probe_live)
 cargoxx_add_test(nix_cmake_scan_parse)
 cargoxx_add_test(nix_cmake_scan_live)
+cargoxx_add_test(conan_probe_parse)
+cargoxx_add_test(conan_probe_live)

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);
+}

tests/conan_probe_parse.cpp

@@ -0,0 +1,81 @@
+#include <catch2/catch_test_macros.hpp>
+
+import cargoxx.resolver;
+import cargoxx.util;
+import std;
+
+using cargoxx::resolver::parse_conanfile;
+using cargoxx::util::ErrorCode;
+
+TEST_CASE("parse_conanfile picks up modern set_property form", "[resolver][conan]") {
+    constexpr std::string_view text = R"PY(
+from conan import ConanFile
+
+class FmtConan(ConanFile):
+    name = "fmt"
+    def package_info(self):
+        self.cpp_info.set_property("cmake_file_name", "fmt")
+        self.cpp_info.set_property("cmake_target_name", "fmt::fmt")
+)PY";
+
+    auto r = parse_conanfile(text, "fmt");
+    REQUIRE(r.has_value());
+    REQUIRE(r->find_package == "fmt CONFIG REQUIRED");
+    REQUIRE(r->targets == std::vector<std::string>{"fmt::fmt"});
+}
+
+TEST_CASE("parse_conanfile picks up legacy names[] form", "[resolver][conan]") {
+    constexpr std::string_view text = R"PY(
+class SpdlogConan(ConanFile):
+    def package_info(self):
+        self.cpp_info.names["cmake_find_package"] = "spdlog"
+)PY";
+
+    auto r = parse_conanfile(text, "spdlog");
+    REQUIRE(r.has_value());
+    REQUIRE(r->find_package == "spdlog CONFIG REQUIRED");
+    // Derived target heuristic: spdlog::spdlog
+    REQUIRE(r->targets == std::vector<std::string>{"spdlog::spdlog"});
+}
+
+TEST_CASE("parse_conanfile derives cmake_file_name from a colon-namespaced target",
+          "[resolver][conan]") {
+    constexpr std::string_view text = R"PY(
+self.cpp_info.set_property("cmake_target_name", "Boost::filesystem")
+)PY";
+    auto r = parse_conanfile(text, "boost");
+    REQUIRE(r.has_value());
+    REQUIRE(r->find_package == "Boost CONFIG REQUIRED");
+    REQUIRE(r->targets == std::vector<std::string>{"Boost::filesystem"});
+}
+
+TEST_CASE("parse_conanfile falls back to the package name when nothing matches",
+          "[resolver][conan]") {
+    constexpr std::string_view text = R"PY(
+# This recipe gives us nothing useful at the cpp_info level.
+class OpaqueConan(ConanFile):
+    name = "opaque"
+)PY";
+    auto r = parse_conanfile(text, "opaque");
+    REQUIRE(r.has_value());
+    REQUIRE(r->find_package == "opaque CONFIG REQUIRED");
+    REQUIRE(r->targets == std::vector<std::string>{"opaque::opaque"});
+}
+
+TEST_CASE("parse_conanfile errors when no information AND no fallback",
+          "[resolver][conan]") {
+    auto r = parse_conanfile("# nothing here", "");
+    REQUIRE_FALSE(r.has_value());
+    REQUIRE(r.error().code == ErrorCode::ResolutionUnknownPackage);
+}
+
+TEST_CASE("parse_conanfile accepts single-quoted strings", "[resolver][conan]") {
+    constexpr std::string_view text = R"PY(
+self.cpp_info.set_property('cmake_target_name', 'absl::strings')
+self.cpp_info.set_property('cmake_file_name', 'absl')
+)PY";
+    auto r = parse_conanfile(text, "abseil");
+    REQUIRE(r.has_value());
+    REQUIRE(r->find_package == "absl CONFIG REQUIRED");
+    REQUIRE(r->targets == std::vector<std::string>{"absl::strings"});
+}