[M5+] add resolver::nix_cmake_scan

src/resolver/resolver.cppm

@@ -26,4 +26,29 @@ auto parse_nix_eval_json(std::string_view attr, std::string_view json)
 // `ResolutionNetworkError` on timeout or evaluator errors.
 auto nixpkgs_probe(const std::string& attr) -> util::Result<NixpkgsInfo>;
 
+// One CMake config-file's IMPORTED targets together with the find_package
+// expression derived from its filename stem.
+struct NixCmakeCandidate {
+    std::string find_package;        // e.g. "fmt CONFIG REQUIRED"
+    std::vector<std::string> targets; // e.g. ["fmt::fmt"]
+    std::filesystem::path config_file; // the *Config.cmake we scraped
+};
+
+// Pure: scan a single CMake config text for `add_library(... IMPORTED)`
+// target names. ALIAS targets are also collected so canonical
+// `<alias>::<member>` forms get picked up.
+auto scan_imported_targets(std::string_view config_text) -> std::vector<std::string>;
+
+// Pure: turn a CMake config filename into the find_package name.
+// `fmtConfig.cmake` / `fmt-config.cmake` -> `fmt`.
+auto config_stem_to_package(std::string_view filename) -> std::string;
+
+// Walks <store_path>/lib/cmake/** for *Config.cmake / *-config.cmake files.
+// Picks the candidate whose derived package name best matches `package_name`
+// (exact case-insensitive equality > prefix > first non-empty target list).
+// Returns ResolutionUnknownPackage when nothing usable is found.
+auto nix_cmake_scan(const std::filesystem::path& store_path,
+                    const std::string& package_name)
+    -> util::Result<NixCmakeCandidate>;
+
 } // namespace cargoxx::resolver