1 files changed, 166 insertions, 32 deletions

diff --git a/src/libstore/content-address.hh b/src/libstore/content-address.hh
index 368a7ec48..2f98950fb 100644
--- a/src/libstore/content-address.hh
+++ b/src/libstore/content-address.hh
@@ -3,12 +3,30 @@
 
 #include <variant>
 #include "hash.hh"
+#include "path.hh"
 #include "comparator.hh"
 
 namespace nix {
 
+/*
+ * Content addressing method
+ */
+
+/* We only have one way to hash text with references, so this is a single-value
+   type, mainly useful with std::variant.
+*/
+
+/**
+ * The single way we can serialize "text" file system objects.
+ *
+ * Somewhat obscure, used by \ref Derivation derivations and
+ * `builtins.toFile` currently.
+ */
+struct TextHashMethod : std::monostate { };
+
 /**
- * An enumeration of the ways we can serialize file system objects.
+ * An enumeration of the main ways we can serialize file system
+ * objects.
  */
 enum struct FileIngestionMethod : uint8_t {
     /**
@@ -23,6 +41,53 @@ enum struct FileIngestionMethod : uint8_t {
 };
 
 /**
+ * Compute the prefix to the hash algorithm which indicates how the
+ * files were ingested.
+ */
+std::string makeFileIngestionPrefix(FileIngestionMethod m);
+
+struct FixedOutputHashMethod {
+    FileIngestionMethod fileIngestionMethod;
+    HashType hashType;
+
+    GENERATE_CMP(FixedOutputHashMethod, me->fileIngestionMethod, me->hashType);
+};
+
+/**
+ * An enumeration of all the ways we can serialize file system objects.
+ *
+ * Just the type of a content address. Combine with the hash itself, and
+ * we have a `ContentAddress` as defined below. Combine that, in turn,
+ * with info on references, and we have `ContentAddressWithReferences`,
+ * as defined further below.
+ */
+struct ContentAddressMethod
+{
+    typedef std::variant<
+        TextHashMethod,
+        FixedOutputHashMethod
+    > Raw;
+
+    Raw raw;
+
+    GENERATE_CMP(ContentAddressMethod, me->raw);
+
+    /* The moral equivalent of `using Raw::Raw;` */
+    ContentAddressMethod(auto &&... arg)
+        : raw(std::forward<decltype(arg)>(arg)...)
+    { }
+
+    static ContentAddressMethod parse(std::string_view rawCaMethod);
+
+    std::string render() const;
+};
+
+
+/*
+ * Mini content address
+ */
+
+/**
  * Somewhat obscure, used by \ref Derivation derivations and
  * `builtins.toFile` currently.
  */
@@ -36,7 +101,7 @@ struct TextHash {
 };
 
 /**
- * For path computed by makeFixedOutputPath.
+ * Used by most store objects that are content-addressed.
  */
 struct FixedOutputHash {
     /**
@@ -65,41 +130,96 @@ struct FixedOutputHash {
  * - ‘fixed:<r?>:<ht>:<h>’: For paths computed by
  *   Store::makeFixedOutputPath() / Store::addToStore().
  */
-typedef std::variant<
-    TextHash,
-    FixedOutputHash
-> ContentAddress;
+struct ContentAddress
+{
+    typedef std::variant<
+        TextHash,
+        FixedOutputHash
+    > Raw;
 
-/**
- * Compute the prefix to the hash algorithm which indicates how the
- * files were ingested.
+    Raw raw;
+
+    GENERATE_CMP(ContentAddress, me->raw);
+
+    /* The moral equivalent of `using Raw::Raw;` */
+    ContentAddress(auto &&... arg)
+        : raw(std::forward<decltype(arg)>(arg)...)
+    { }
+
+    /**
+     * Compute the content-addressability assertion (ValidPathInfo::ca) for
+     * paths created by Store::makeFixedOutputPath() / Store::addToStore().
+     */
+    std::string render() const;
+
+    static ContentAddress parse(std::string_view rawCa);
+
+    static std::optional<ContentAddress> parseOpt(std::string_view rawCaOpt);
+
+    const Hash & getHash() const;
+};
+
+std::string renderContentAddress(std::optional<ContentAddress> ca);
+
+
+/*
+ * Full content address
+ *
+ * See the schema for store paths in store-api.cc
  */
-std::string makeFileIngestionPrefix(const FileIngestionMethod m);
 
 /**
- * Compute the content-addressability assertion (ValidPathInfo::ca) for
- * paths created by Store::makeFixedOutputPath() / Store::addToStore().
+ * A set of references to other store objects.
+ *
+ * References to other store objects are tracked with store paths, self
+ * references however are tracked with a boolean.
  */
-std::string makeFixedOutputCA(FileIngestionMethod method, const Hash & hash);
+struct StoreReferences {
+    /**
+     * References to other store objects
+     */
+    StorePathSet others;
 
-std::string renderContentAddress(ContentAddress ca);
+    /**
+     * Reference to this store object
+     */
+    bool self = false;
 
-std::string renderContentAddress(std::optional<ContentAddress> ca);
+    /**
+     * @return true iff no references, i.e. others is empty and self is
+     * false.
+     */
+    bool empty() const;
 
-ContentAddress parseContentAddress(std::string_view rawCa);
+    /**
+     * Returns the numbers of references, i.e. the size of others + 1
+     * iff self is true.
+     */
+    size_t size() const;
 
-std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt);
+    GENERATE_CMP(StoreReferences, me->self, me->others);
+};
 
-Hash getContentAddressHash(const ContentAddress & ca);
+// This matches the additional info that we need for makeTextPath
+struct TextInfo {
+    TextHash hash;
+    /**
+     * References to other store objects only; self references
+     * disallowed
+     */
+    StorePathSet references;
 
-/*
-  We only have one way to hash text with references, so this is single-value
-  type is only useful in std::variant.
-*/
-struct TextHashMethod { };
-struct FixedOutputHashMethod {
-  FileIngestionMethod fileIngestionMethod;
-  HashType hashType;
+    GENERATE_CMP(TextInfo, me->hash, me->references);
+};
+
+struct FixedOutputInfo {
+    FixedOutputHash hash;
+    /**
+     * References to other store objects or this one.
+     */
+    StoreReferences references;
+
+    GENERATE_CMP(FixedOutputInfo, me->hash, me->references);
 };
 
 /**
@@ -107,13 +227,27 @@ struct FixedOutputHashMethod {
  *
  * A ContentAddress without a Hash.
  */
-typedef std::variant<
-    TextHashMethod,
-    FixedOutputHashMethod
-  > ContentAddressMethod;
+struct ContentAddressWithReferences
+{
+    typedef std::variant<
+        TextInfo,
+        FixedOutputInfo
+    > Raw;
+
+    Raw raw;
 
-ContentAddressMethod parseContentAddressMethod(std::string_view rawCaMethod);
+    GENERATE_CMP(ContentAddressWithReferences, me->raw);
 
-std::string renderContentAddressMethod(ContentAddressMethod caMethod);
+    /* The moral equivalent of `using Raw::Raw;` */
+    ContentAddressWithReferences(auto &&... arg)
+        : raw(std::forward<decltype(arg)>(arg)...)
+    { }
+
+    /**
+     * Create a ContentAddressWithReferences from a mere ContentAddress, by
+     * assuming no references in all cases.
+     */
+    static ContentAddressWithReferences withoutRefs(const ContentAddress &);
+};
 
 }