Split out a new libnixflake

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

src/libflake/flake/flakeref.hh

@@ -0,0 +1,113 @@
+#pragma once
+///@file
+
+#include "types.hh"
+#include "hash.hh"
+#include "fetchers.hh"
+#include "outputs-spec.hh"
+
+#include <regex>
+#include <variant>
+
+namespace nix {
+
+class Store;
+
+typedef std::string FlakeId;
+
+/**
+ * A flake reference specifies how to fetch a flake or raw source
+ * (e.g. from a Git repository).  It is created from a URL-like syntax
+ * (e.g. 'github:NixOS/patchelf'), an attrset representation (e.g. '{
+ * type="github"; owner = "NixOS"; repo = "patchelf"; }'), or a local
+ * path.
+ *
+ * Each flake will have a number of FlakeRef objects: one for each
+ * input to the flake.
+ *
+ * The normal method of constructing a FlakeRef is by starting with an
+ * input description (usually the attrs or a url from the flake file),
+ * locating a fetcher for that input, and then capturing the Input
+ * object that fetcher generates (usually via
+ * FlakeRef::fromAttrs(attrs) or parseFlakeRef(url) calls).
+ *
+ * The actual fetch may not have been performed yet (i.e. a FlakeRef may
+ * be lazy), but the fetcher can be invoked at any time via the
+ * FlakeRef to ensure the store is populated with this input.
+ */
+struct FlakeRef
+{
+    /**
+     * Fetcher-specific representation of the input, sufficient to
+     * perform the fetch operation.
+     */
+    fetchers::Input input;
+
+    /**
+     * sub-path within the fetched input that represents this input
+     */
+    Path subdir;
+
+    bool operator==(const FlakeRef & other) const;
+
+    FlakeRef(fetchers::Input && input, const Path & subdir)
+        : input(std::move(input)), subdir(subdir)
+    { }
+
+    // FIXME: change to operator <<.
+    std::string to_string() const;
+
+    fetchers::Attrs toAttrs() const;
+
+    FlakeRef resolve(ref<Store> store) const;
+
+    static FlakeRef fromAttrs(const fetchers::Attrs & attrs);
+
+    std::pair<StorePath, FlakeRef> fetchTree(ref<Store> store) const;
+};
+
+std::ostream & operator << (std::ostream & str, const FlakeRef & flakeRef);
+
+/**
+ * @param baseDir Optional [base directory](https://nixos.org/manual/nix/unstable/glossary#gloss-base-directory)
+ */
+FlakeRef parseFlakeRef(
+    const std::string & url,
+    const std::optional<Path> & baseDir = {},
+    bool allowMissing = false,
+    bool isFlake = true);
+
+/**
+ * @param baseDir Optional [base directory](https://nixos.org/manual/nix/unstable/glossary#gloss-base-directory)
+ */
+std::optional<FlakeRef> maybeParseFlake(
+    const std::string & url, const std::optional<Path> & baseDir = {});
+
+/**
+ * @param baseDir Optional [base directory](https://nixos.org/manual/nix/unstable/glossary#gloss-base-directory)
+ */
+std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
+    const std::string & url,
+    const std::optional<Path> & baseDir = {},
+    bool allowMissing = false,
+    bool isFlake = true);
+
+/**
+ * @param baseDir Optional [base directory](https://nixos.org/manual/nix/unstable/glossary#gloss-base-directory)
+ */
+std::optional<std::pair<FlakeRef, std::string>> maybeParseFlakeRefWithFragment(
+    const std::string & url, const std::optional<Path> & baseDir = {});
+
+/**
+ * @param baseDir Optional [base directory](https://nixos.org/manual/nix/unstable/glossary#gloss-base-directory)
+ */
+std::tuple<FlakeRef, std::string, ExtendedOutputsSpec> parseFlakeRefWithFragmentAndExtendedOutputsSpec(
+    const std::string & url,
+    const std::optional<Path> & baseDir = {},
+    bool allowMissing = false,
+    bool isFlake = true);
+
+const static std::string flakeIdRegexS = "[a-zA-Z][a-zA-Z0-9_-]*";
+extern std::regex flakeIdRegex;
+
+}