[M7] cargoxx vendor + build --offline + path: store-path codegen

Cargoxx.lock

@@ -1,3 +1,5 @@
+flake_utils_rev = '11707dc2f618dd54ca8739b309ec4fc024de578b'
+nixpkgs_rev = 'da5ad661ba4e5ef59ba743f0d112cbc30e474f32'
 version = 1
 
 [[package]]
@@ -6,19 +8,25 @@ name = 'cargoxx'
 version = '0.1.0'
 
 [[package]]
+find_package = 'reproc CONFIG REQUIRED'
 linkdb_source = 'nix-probe'
 name = 'reproc'
 nixpkgs_attr = 'reproc'
+targets = [ 'reproc' ]
 version = '*'
 
 [[package]]
+find_package = 'SQLite3 REQUIRED'
 linkdb_source = 'cmake-findmodule'
 name = 'sqlite'
 nixpkgs_attr = 'sqlite'
+targets = [ 'SQLite::SQLite3' ]
 version = '*'
 
 [[package]]
+find_package = 'Catch2 CONFIG REQUIRED'
 linkdb_source = 'nix-probe'
 name = 'catch2_3'
 nixpkgs_attr = 'catch2_3'
+targets = [ 'Catch2::Catch2', 'Catch2::Catch2WithMain' ]
 version = '*'

build/CMakeLists.txt

@@ -46,9 +46,11 @@ target_sources(cargoxx
         ../src/cli/cmd_remove.cpp
         ../src/cli/cmd_run.cpp
         ../src/cli/cmd_test.cpp
+        ../src/cli/cmd_vendor.cpp
         ../src/cli/run.cpp
         ../src/codegen/cmake.cpp
         ../src/codegen/flake.cpp
+        ../src/codegen/vendor.cpp
         ../src/exec/subprocess.cpp
         ../src/layout/layout.cpp
         ../src/linkdb/database.cpp

src/cli/cli.cppm

@@ -20,7 +20,13 @@ auto cmd_new(const std::string& name, bool lib_only,
 // `overlay_path` lets tests redirect the linkdb overlay away from ~/.cache.
 auto cmd_build(const std::filesystem::path& project_root, bool no_build, bool release,
                std::optional<std::string> target = std::nullopt,
-               std::optional<std::filesystem::path> overlay_path = std::nullopt)
+               std::optional<std::filesystem::path> overlay_path = std::nullopt,
+               bool offline = false,
+               std::optional<std::filesystem::path> vendor = std::nullopt)
+    -> util::Result<void>;
+
+auto cmd_vendor(const std::filesystem::path& project_root,
+                const std::filesystem::path& output)
     -> util::Result<void>;
 
 // Builds the project, picks a binary target, and execs it with `args`.

src/cli/cmd_build.cpp

@@ -177,7 +177,8 @@ auto run_nix_cmake(const fs::path& project_root, const std::vector<std::string>&
 
 auto cmd_build(const fs::path& project_root, bool no_build, bool release,
                std::optional<std::string> target,
-               std::optional<fs::path> overlay_path) -> util::Result<void> {
+               std::optional<fs::path> overlay_path, bool offline,
+               std::optional<fs::path> vendor) -> util::Result<void> {
     auto manifest_path = project_root / "Cargoxx.toml";
     auto m = manifest::parse(manifest_path);
     if (!m) {
@@ -283,6 +284,24 @@ auto cmd_build(const fs::path& project_root, bool no_build, bool release,
     }
     auto lock = merge_lockfile(*m, *recipes, *dev_recipes, prior);
 
+    std::optional<codegen::VendorIndex> vendor_index;
+    if (offline) {
+        auto vendor_path = vendor.value_or(project_root / "vendor.toml");
+        if (std::error_code v_ec; !fs::exists(vendor_path, v_ec)) {
+            return std::unexpected(io_error(
+                std::format("--offline requires vendor.toml; expected at '{}'",
+                            vendor_path.string()),
+                vendor_path));
+        }
+        std::ifstream in_file{vendor_path};
+        std::string body{std::istreambuf_iterator<char>(in_file), {}};
+        auto parsed = codegen::parse_vendor_toml(body);
+        if (!parsed) {
+            return std::unexpected(parsed.error());
+        }
+        vendor_index = std::move(*parsed);
+    }
+
     codegen::GenerateInputs in{
         .manifest = *m,
         .layout = *layout_result,
@@ -290,6 +309,7 @@ auto cmd_build(const fs::path& project_root, bool no_build, bool release,
         .recipes = *recipes,
         .dev_recipes = *dev_recipes,
         .project_root = project_root,
+        .vendor = vendor_index,
     };
     auto flake_text = codegen::flake_nix(in);
     auto cmake_text = codegen::cmake_lists(in);
@@ -326,16 +346,41 @@ auto cmd_build(const fs::path& project_root, bool no_build, bool release,
         "-G", "Ninja",
         std::format("-DCMAKE_BUILD_TYPE={}", profile_cap),
     };
-    if (auto r = run_nix_cmake(project_root, configure_args, "configure"); !r) {
-        return std::unexpected(r.error());
-    }
-
     std::vector<std::string> build_args{"--build", build_dir};
     if (target) {
         build_args.push_back("--target");
         build_args.push_back(*target);
     }
-    if (auto r = run_nix_cmake(project_root, build_args, "build"); !r) {
+
+    auto run_cmake = [&](const std::vector<std::string>& args,
+                          std::string_view phase) -> util::Result<void> {
+        if (offline) {
+            auto r = exec::run("cmake", args,
+                                exec::ExecOptions{
+                                    .cwd = project_root,
+                                    .env_overrides = {},
+                                    .timeout = std::nullopt,
+                                    .inherit_stdio = true,
+                                });
+            if (!r) {
+                return std::unexpected(r.error());
+            }
+            if (r->exit_code != 0) {
+                return std::unexpected(util::Error{
+                    util::ErrorCode::BuildCmakeFailed,
+                    std::format("cmake {} failed (exit {})", phase, r->exit_code),
+                    "", std::nullopt, std::nullopt,
+                });
+            }
+            return {};
+        }
+        return run_nix_cmake(project_root, args, phase);
+    };
+
+    if (auto r = run_cmake(configure_args, "configure"); !r) {
+        return std::unexpected(r.error());
+    }
+    if (auto r = run_cmake(build_args, "build"); !r) {
         return std::unexpected(r.error());
     }
 

src/cli/cmd_vendor.cpp

@@ -0,0 +1,128 @@
+module cargoxx.cli;
+
+import std;
+import cargoxx.lockfile;
+import cargoxx.resolver;
+import cargoxx.util;
+
+namespace cargoxx::cli {
+
+namespace fs = std::filesystem;
+
+namespace {
+
+auto error(util::ErrorCode code, std::string msg, fs::path path) -> util::Error {
+    return util::Error{code, std::move(msg), "", std::move(path), std::nullopt};
+}
+
+auto escape_toml(std::string_view s) -> std::string {
+    std::string out;
+    out.reserve(s.size() + 2);
+    out += '"';
+    for (char c : s) {
+        if (c == '"' || c == '\\') {
+            out += '\\';
+        }
+        out += c;
+    }
+    out += '"';
+    return out;
+}
+
+} // namespace
+
+auto cmd_vendor(const fs::path& project_root, const fs::path& output)
+    -> util::Result<void> {
+    auto lock_path = project_root / "Cargoxx.lock";
+    auto lock = lockfile::parse(lock_path);
+    if (!lock) {
+        return std::unexpected(lock.error());
+    }
+    if (!lock->nixpkgs_rev_pin || lock->nixpkgs_rev_pin->empty()) {
+        return std::unexpected(error(
+            util::ErrorCode::ManifestInvalidField,
+            "Cargoxx.lock has no top-level nixpkgs_rev — run cargoxx build "
+            "online first to pin it",
+            lock_path));
+    }
+    if (!lock->flake_utils_rev_pin || lock->flake_utils_rev_pin->empty()) {
+        return std::unexpected(error(
+            util::ErrorCode::ManifestInvalidField,
+            "Cargoxx.lock has no top-level flake_utils_rev",
+            lock_path));
+    }
+
+    auto nixpkgs_src = resolver::realize_flake_source(
+        std::format("github:NixOS/nixpkgs/{}", *lock->nixpkgs_rev_pin));
+    if (!nixpkgs_src) {
+        return std::unexpected(nixpkgs_src.error());
+    }
+    auto flake_utils_src = resolver::realize_flake_source(
+        std::format("github:numtide/flake-utils/{}", *lock->flake_utils_rev_pin));
+    if (!flake_utils_src) {
+        return std::unexpected(flake_utils_src.error());
+    }
+
+    std::string body;
+    body += "schema = 1\n\n";
+    body += "[nixpkgs]\n";
+    body += std::format("rev = {}\n", escape_toml(*lock->nixpkgs_rev_pin));
+    body += std::format("store_path = {}\n\n", escape_toml(*nixpkgs_src));
+    body += "[flake_utils]\n";
+    body += std::format("rev = {}\n", escape_toml(*lock->flake_utils_rev_pin));
+    body += std::format("store_path = {}\n", escape_toml(*flake_utils_src));
+
+    for (const auto& p : lock->packages) {
+        if (!p.linkdb_source) {
+            continue;
+        }
+        if (!p.nixpkgs_attr) {
+            return std::unexpected(error(
+                util::ErrorCode::ManifestInvalidField,
+                std::format("lockfile dep '{}' has no nixpkgs_attr", p.name),
+                lock_path));
+        }
+        auto rev = p.nixpkgs_rev.has_value() && !p.nixpkgs_rev->empty()
+                       ? *p.nixpkgs_rev
+                       : *lock->nixpkgs_rev_pin;
+        auto store = resolver::realize_path_at_rev(rev, *p.nixpkgs_attr);
+        if (!store) {
+            return std::unexpected(store.error());
+        }
+        std::optional<std::string> dev_path;
+        if (auto d = resolver::realize_path_at_rev(
+                rev, std::format("{}.dev", *p.nixpkgs_attr));
+            d) {
+            dev_path = *d;
+        }
+
+        body += "\n[[dep]]\n";
+        body += std::format("name = {}\n", escape_toml(p.name));
+        body += std::format("nixpkgs_attr = {}\n", escape_toml(*p.nixpkgs_attr));
+        body += std::format("nixpkgs_rev = {}\n", escape_toml(rev));
+        body += std::format("store_path = {}\n", escape_toml(*store));
+        if (dev_path) {
+            body += std::format("dev_path = {}\n", escape_toml(*dev_path));
+        }
+    }
+
+    std::error_code ec;
+    fs::create_directories(output.parent_path(), ec);
+    std::ofstream out{output};
+    if (!out) {
+        return std::unexpected(error(
+            util::ErrorCode::Internal,
+            std::format("cannot open vendor file for writing: {}",
+                        output.string()),
+            output));
+    }
+    out << body;
+    if (!out) {
+        return std::unexpected(error(
+            util::ErrorCode::Internal,
+            std::format("write failed: {}", output.string()), output));
+    }
+    return {};
+}
+
+} // namespace cargoxx::cli

src/cli/run.cpp

@@ -23,13 +23,26 @@ auto run(int argc, char** argv) -> int {
         "build", "Generate flake.nix and build/CMakeLists.txt; build with nix+cmake");
     bool build_no_build = false;
     bool build_release = false;
+    bool build_offline = false;
     std::string build_target;
+    std::string build_vendor;
     build_cmd->add_flag("--no-build", build_no_build,
                         "Generate files only; do not invoke nix/cmake");
     build_cmd->add_flag("--release", build_release, "Build the release profile");
+    build_cmd->add_flag("--offline", build_offline,
+                        "Skip network probes and nix develop wrappers. "
+                        "Reads vendor.toml for store-path inputs.");
+    build_cmd->add_option("--vendor", build_vendor,
+                          "Path to vendor.toml (used with --offline; default ./vendor.toml)");
     build_cmd->add_option("--target", build_target,
                           "Build a specific target (passed to cmake --build)");
 
+    auto* vendor_cmd = app.add_subcommand(
+        "vendor", "Resolve every locked dependency into /nix/store and write vendor.toml");
+    std::string vendor_output;
+    vendor_cmd->add_option("--output", vendor_output,
+                            "Path to write vendor.toml (default ./vendor.toml)");
+
     auto* run_cmd = app.add_subcommand("run", "Build and run a binary target");
     bool run_release = false;
     std::string run_bin;
@@ -109,7 +122,12 @@ auto run(int argc, char** argv) -> int {
         if (!build_target.empty()) {
             target = build_target;
         }
-        auto r = cmd_build(cwd, build_no_build, build_release, target);
+        std::optional<std::filesystem::path> vendor_path;
+        if (!build_vendor.empty()) {
+            vendor_path = build_vendor;
+        }
+        auto r = cmd_build(cwd, build_no_build, build_release, target,
+                            std::nullopt, build_offline, vendor_path);
         if (!r) {
             std::cerr << util::format(r.error());
             return 1;
@@ -122,6 +140,18 @@ auto run(int argc, char** argv) -> int {
         return 0;
     }
 
+    if (*vendor_cmd) {
+        auto out = vendor_output.empty() ? cwd / "vendor.toml"
+                                          : std::filesystem::path{vendor_output};
+        auto r = cmd_vendor(cwd, out);
+        if (!r) {
+            std::cerr << util::format(r.error());
+            return 1;
+        }
+        std::cout << std::format("    Wrote {}\n", out.string());
+        return 0;
+    }
+
     if (*run_cmd) {
         std::optional<std::string> bin;
         if (!run_bin.empty()) {

src/codegen/codegen.cppm

@@ -9,6 +9,16 @@ import cargoxx.lockfile;
 
 export namespace cargoxx::codegen {
 
+// When set, codegen emits the generated flake's nixpkgs / flake-utils
+// inputs as `path:/nix/store/...` references (already-realized source
+// paths) instead of `github:NixOS/nixpkgs/<rev>` URLs. This makes the
+// inner build hermetic — no network and no nix daemon access required.
+struct VendorIndex {
+    std::string nixpkgs_store_path;
+    std::string flake_utils_store_path;
+    std::unordered_map<std::string, std::string> dep_store_paths; // by attr
+};
+
 // All inputs the generators need. Held by const reference; the caller owns
 // the underlying objects. Not copyable.
 struct GenerateInputs {
@@ -18,9 +28,14 @@ struct GenerateInputs {
     std::vector<linkdb::Recipe> recipes; // one per manifest dep, same order
     std::vector<linkdb::Recipe> dev_recipes; // one per dev_dependency, same order
     std::filesystem::path project_root;
+    std::optional<VendorIndex> vendor;
 };
 
 auto flake_nix(const GenerateInputs& in) -> std::string;
 auto cmake_lists(const GenerateInputs& in) -> std::string;
 
+// Pure: parses a vendor.toml (see cmd_vendor) into a VendorIndex.
+auto parse_vendor_toml(std::string_view body)
+    -> util::Result<VendorIndex>;
+
 } // namespace cargoxx::codegen

src/codegen/flake.cpp

@@ -100,22 +100,36 @@ auto pinned_inputs_dedup(const std::vector<DepBinding>& bindings)
 }
 
 auto emit_inputs_block(const std::vector<const DepBinding*>& pinned,
-                        const lockfile::Lockfile& lock) -> std::string {
-    auto nixpkgs_url =
-        lock.nixpkgs_rev_pin && !lock.nixpkgs_rev_pin->empty()
-            ? std::format("github:NixOS/nixpkgs/{}", *lock.nixpkgs_rev_pin)
-            : std::string{"github:NixOS/nixpkgs/nixos-unstable"};
-    auto flake_utils_url =
-        lock.flake_utils_rev_pin && !lock.flake_utils_rev_pin->empty()
-            ? std::format("github:numtide/flake-utils/{}",
-                          *lock.flake_utils_rev_pin)
-            : std::string{"github:numtide/flake-utils"};
+                        const lockfile::Lockfile& lock,
+                        const std::optional<VendorIndex>& vendor)
+    -> std::string {
+    auto nixpkgs_url = [&]() -> std::string {
+        if (vendor && !vendor->nixpkgs_store_path.empty()) {
+            return std::format("path:{}", vendor->nixpkgs_store_path);
+        }
+        if (lock.nixpkgs_rev_pin && !lock.nixpkgs_rev_pin->empty()) {
+            return std::format("github:NixOS/nixpkgs/{}", *lock.nixpkgs_rev_pin);
+        }
+        return "github:NixOS/nixpkgs/nixos-unstable";
+    }();
+    auto flake_utils_url = [&]() -> std::string {
+        if (vendor && !vendor->flake_utils_store_path.empty()) {
+            return std::format("path:{}", vendor->flake_utils_store_path);
+        }
+        if (lock.flake_utils_rev_pin && !lock.flake_utils_rev_pin->empty()) {
+            return std::format("github:numtide/flake-utils/{}",
+                                *lock.flake_utils_rev_pin);
+        }
+        return "github:numtide/flake-utils";
+    }();
     std::string out =
         "  inputs = {\n"
         + std::format("    nixpkgs.url = \"{}\";\n", nixpkgs_url);
-    for (const auto* b : pinned) {
-        out += std::format("    {}.url = \"github:NixOS/nixpkgs/{}\";\n",
-                           b->sanitized, *b->rev);
+    if (!vendor) {
+        for (const auto* b : pinned) {
+            out += std::format("    {}.url = \"github:NixOS/nixpkgs/{}\";\n",
+                               b->sanitized, *b->rev);
+        }
     }
     out += std::format("    flake-utils.url = \"{}\";\n", flake_utils_url);
     out += "  };\n";
@@ -171,7 +185,7 @@ auto flake_nix(const GenerateInputs& in) -> std::string {
     out += "{\n";
     out += std::format("  description = \"{}\";\n\n", in.manifest.package.name);
 
-    out += emit_inputs_block(pinned, in.lock);
+    out += emit_inputs_block(pinned, in.lock, in.vendor);
 
     const bool any_pkg_config =
         std::ranges::any_of(in.recipes,

src/codegen/vendor.cpp

@@ -0,0 +1,69 @@
+module;
+
+#include <toml.hpp>
+
+module cargoxx.codegen;
+
+import std;
+import cargoxx.util;
+
+namespace cargoxx::codegen {
+
+auto parse_vendor_toml(std::string_view body) -> util::Result<VendorIndex> {
+    toml::table root;
+    try {
+        root = toml::parse(body);
+    } catch (const toml::parse_error& e) {
+        return std::unexpected(util::Error{
+            util::ErrorCode::ManifestParseError,
+            std::format("vendor.toml is not valid TOML: {}", e.description()),
+            "", std::nullopt, std::nullopt,
+        });
+    }
+
+    auto missing = [](std::string msg) {
+        return util::Error{
+            util::ErrorCode::ManifestInvalidField, std::move(msg), "",
+            std::nullopt, std::nullopt,
+        };
+    };
+
+    VendorIndex out;
+    if (const auto* tbl = root["nixpkgs"].as_table()) {
+        if (auto v = (*tbl)["store_path"].value<std::string>()) {
+            out.nixpkgs_store_path = *v;
+        } else {
+            return std::unexpected(missing("vendor.toml: [nixpkgs].store_path is required"));
+        }
+    } else {
+        return std::unexpected(missing("vendor.toml: [nixpkgs] table is required"));
+    }
+    if (const auto* tbl = root["flake_utils"].as_table()) {
+        if (auto v = (*tbl)["store_path"].value<std::string>()) {
+            out.flake_utils_store_path = *v;
+        } else {
+            return std::unexpected(missing("vendor.toml: [flake_utils].store_path is required"));
+        }
+    } else {
+        return std::unexpected(missing("vendor.toml: [flake_utils] table is required"));
+    }
+
+    if (const auto* arr = root["dep"].as_array()) {
+        for (const auto& el : *arr) {
+            const auto* tbl = el.as_table();
+            if (!tbl) {
+                return std::unexpected(missing("vendor.toml: [[dep]] entries must be tables"));
+            }
+            auto attr = (*tbl)["nixpkgs_attr"].value<std::string>();
+            auto path = (*tbl)["store_path"].value<std::string>();
+            if (!attr || !path) {
+                return std::unexpected(missing(
+                    "vendor.toml: each [[dep]] needs nixpkgs_attr and store_path"));
+            }
+            out.dep_store_paths.emplace(*attr, *path);
+        }
+    }
+    return out;
+}
+
+} // namespace cargoxx::codegen

src/resolver/nixpkgs_probe.cpp

@@ -162,4 +162,95 @@ auto realize_path(const std::string& flake_attr) -> util::Result<std::string> {
     return path;
 }
 
+auto realize_path_at_rev(const std::string& rev, const std::string& attr)
+    -> util::Result<std::string> {
+    if (rev.empty() || attr.empty()) {
+        return std::unexpected(make_error(
+            util::ErrorCode::ResolutionUnknownPackage,
+            "realize_path_at_rev: rev and attr must be non-empty"));
+    }
+    std::vector<std::string> args{
+        "--extra-experimental-features", "nix-command flakes",
+        "build", std::format("github:NixOS/nixpkgs/{}#{}", rev, attr),
+        "--no-link", "--print-out-paths",
+    };
+    auto r = exec::run("nix", args,
+                       exec::ExecOptions{
+                           .cwd = {},
+                           .env_overrides = {},
+                           .timeout = std::chrono::seconds{600},
+                           .inherit_stdio = false,
+                       });
+    if (!r) {
+        return std::unexpected(r.error());
+    }
+    if (r->exit_code != 0) {
+        if (looks_like_missing_attribute(r->stderr_text)) {
+            return std::unexpected(make_error(
+                util::ErrorCode::ResolutionUnknownPackage,
+                std::format("nixpkgs/{} has no attribute '{}'", rev, attr)));
+        }
+        return std::unexpected(make_error(
+            util::ErrorCode::ResolutionNetworkError,
+            std::format("nix build failed (exit {}): {}", r->exit_code,
+                        r->stderr_text)));
+    }
+    auto path = r->stdout_text;
+    while (!path.empty() && (path.back() == '\n' || path.back() == ' ')) {
+        path.pop_back();
+    }
+    if (path.empty()) {
+        return std::unexpected(make_error(
+            util::ErrorCode::ResolutionNetworkError,
+            std::format("nix build emitted no path for '{}#{}'", rev, attr)));
+    }
+    return path;
+}
+
+auto realize_flake_source(const std::string& flake_ref)
+    -> util::Result<std::string> {
+    if (flake_ref.empty()) {
+        return std::unexpected(make_error(
+            util::ErrorCode::ResolutionUnknownPackage,
+            "realize_flake_source: flake_ref is empty"));
+    }
+    std::vector<std::string> args{
+        "--extra-experimental-features", "nix-command flakes",
+        "flake", "prefetch", flake_ref, "--json",
+    };
+    auto r = exec::run("nix", args,
+                       exec::ExecOptions{
+                           .cwd = {},
+                           .env_overrides = {},
+                           .timeout = std::chrono::seconds{300},
+                           .inherit_stdio = false,
+                       });
+    if (!r) {
+        return std::unexpected(r.error());
+    }
+    if (r->exit_code != 0) {
+        return std::unexpected(make_error(
+            util::ErrorCode::ResolutionNetworkError,
+            std::format("nix flake prefetch failed (exit {}): {}",
+                        r->exit_code, r->stderr_text)));
+    }
+    std::string_view body = r->stdout_text;
+    constexpr std::string_view key = "\"storePath\":\"";
+    auto pos = body.find(key);
+    if (pos == std::string_view::npos) {
+        return std::unexpected(make_error(
+            util::ErrorCode::ResolutionNetworkError,
+            std::format("nix flake prefetch emitted no storePath for '{}'",
+                        flake_ref)));
+    }
+    pos += key.size();
+    auto end = body.find('"', pos);
+    if (end == std::string_view::npos) {
+        return std::unexpected(make_error(
+            util::ErrorCode::ResolutionNetworkError,
+            "nix flake prefetch JSON malformed"));
+    }
+    return std::string{body.substr(pos, end - pos)};
+}
+
 } // namespace cargoxx::resolver

src/resolver/resolver.cppm

@@ -45,6 +45,20 @@ auto nixpkgs_probe(const std::string& attr) -> util::Result<NixpkgsInfo>;
 // for build / network errors.
 auto realize_path(const std::string& flake_attr) -> util::Result<std::string>;
 
+// Like `realize_path`, but pins the nixpkgs revision instead of using the
+// registry alias. Builds `github:NixOS/nixpkgs/<rev>#<attr>` and returns
+// the resulting `/nix/store/...` path. Used by the vendor subcommand to
+// materialize each lockfile-pinned dep without depending on the user's
+// flake registry.
+auto realize_path_at_rev(const std::string& rev, const std::string& attr)
+    -> util::Result<std::string>;
+
+// Returns the source store path for `github:NixOS/nixpkgs/<rev>` (the
+// path Nix would set as `nixpkgs.outPath` when imported). Used by the
+// vendor subcommand to record nixpkgs/flake-utils source locations.
+auto realize_flake_source(const std::string& flake_ref)
+    -> util::Result<std::string>;
+
 // One CMake config-file's IMPORTED targets together with the find_package
 // expression derived from its filename stem.
 struct NixCmakeCandidate {