search: CPS_PATH is a prefix, not an absolute path

This means it does not work like pkg-config's `PKG_CONFIG_PATH`, but
like CMake's `-DCMAKE_PREFIX_PATH`.

See CPS issue: cps-org/cps#45

Author: dcbaker

src/search.cpp

@@ -70,17 +70,20 @@ namespace search {
         }
 
         const std::vector<fs::path> search_paths() {
-            std::vector<fs::path> paths;
+            // TODO: Windows paths
+            // TODO: MacOS paths
+            std::vector<fs::path> roots;
             if (const char * env_c = std::getenv("CPS_PATH")) {
                 auto && env = utils::split(env_c);
-                paths.insert(paths.end(), env.begin(), env.end());
+                roots.insert(roots.end(), env.begin(), env.end());
             }
-            // TODO: lib need to be not hard coded
-            paths.emplace_back(fs::path{"/usr"} / platform::libdir() / "cps");
-            paths.emplace_back("/usr/share/cps");
-            // TODO: Windows paths
-            // TODO: MacOS paths
+            roots.emplace_back("/usr");
 
+            std::vector<fs::path> paths;
+            for (auto && root : roots) {
+                paths.emplace_back(root / platform::libdir() / "cps");
+                paths.emplace_back(root / "share/cps");
+            }
             return paths;
         }
 
@@ -100,12 +103,11 @@ namespace search {
             // dependency?
             auto && paths = search_paths();
             std::vector<fs::path> found{};
-            for (auto && prefix : paths) {
+            for (auto && dir : paths) {
                 // TODO: <prefix>/<libdir>/cps/<name-like>/
                 // TODO: <prefix>/share/cps/<name-like>/
                 // TODO: <prefix>/share/cps/
 
-                const fs::path dir = prefix / platform::libdir() / "cps";
                 if (fs::is_directory(dir)) {
                     // TODO: <name-like>
                     const fs::path file = dir / fmt::format("{}.cps", name);