Improve support for relative path inputs

doc/manual/rl-next/relative-path-flakes.md

@@ -0,0 +1,12 @@
+---
+synopsis: "Support for relative path inputs"
+prs: [10089]
+---
+
+Flakes can now refer to other flakes in the same repository using relative paths, e.g.
+```nix
+inputs.foo.url = "path:./foo";
+```
+uses the flake in the `foo` subdirectory of the referring flake. For more information, see the documentation on [the `path` flake input type](@docroot@/command-ref/new-cli/nix3-flake.md#path-fetcher).
+
+This feature required a change to the lock file format. Previous Nix versions will not be able to use lock files that have locks for relative path inputs in them.

src/libexpr/call-flake.nix

@@ -41,10 +41,17 @@ let
       (key: node:
         let
 
+          parentNode = allNodes.${getInputByPath lockFile.root node.parent};
+
           sourceInfo =
             if overrides ? ${key}
             then
               overrides.${key}.sourceInfo
+            else if node.locked.type == "path" && builtins.substring 0 1 node.locked.path != "/"
+            then
+              parentNode.sourceInfo // {
+                outPath = parentNode.outPath + ("/" + node.locked.path);
+              }
             else
               # FIXME: remove obsolete node.info.
               # Note: lock file entries are always final.

src/libfetchers/fetchers.cc

@@ -166,6 +166,12 @@ bool Input::isFinal() const
     return maybeGetBoolAttr(attrs, "__final").value_or(false);
 }
 
+std::optional<std::string> Input::isRelative() const
+{
+    assert(scheme);
+    return scheme->isRelative(*this);
+}
+
 Attrs Input::toAttrs() const
 {
     return attrs;

src/libfetchers/fetchers.hh

@@ -41,11 +41,6 @@ struct Input
     std::shared_ptr<InputScheme> scheme; // note: can be null
     Attrs attrs;
 
-    /**
-     * path of the parent of this input, used for relative path resolution
-     */
-    std::optional<Path> parent;
-
     /**
      * Cached result of getFingerprint().
      */
@@ -104,6 +99,12 @@ public:
     bool isConsideredLocked(
         const Settings & settings) const;
 
+    /**
+     * Only for relative path flakes, i.e. 'path:./foo', returns the
+     * relative path, i.e. './foo'.
+     */
+    std::optional<std::string> isRelative() const;
+
     /**
      * Return whether this is a "final" input, meaning that fetching
      * it will not add, remove or change any attributes. (See
@@ -269,6 +270,9 @@ struct InputScheme
 
     virtual bool isLocked(const Input & input) const
     { return false; }
+
+    virtual std::optional<std::string> isRelative(const Input & input) const
+    { return std::nullopt; }
 };
 
 void registerInputScheme(std::shared_ptr<InputScheme> && fetcher);

src/libfetchers/path.cc

@@ -91,10 +91,10 @@ struct PathInputScheme : InputScheme
         std::string_view contents,
         std::optional<std::string> commitMsg) const override
     {
-        writeFile((CanonPath(getAbsPath(input)) / path).abs(), contents);
+        writeFile(getAbsPath(input) / path.rel(), contents);
     }
 
-    std::optional<std::string> isRelative(const Input & input) const
+    std::optional<std::string> isRelative(const Input & input) const override
     {
         auto path = getStrAttr(input.attrs, "path");
         if (isAbsolute(path))
@@ -108,44 +108,27 @@ struct PathInputScheme : InputScheme
         return (bool) input.getNarHash();
     }
 
-    CanonPath getAbsPath(const Input & input) const
+    std::filesystem::path getAbsPath(const Input & input) const
     {
         auto path = getStrAttr(input.attrs, "path");
 
-        if (path[0] == '/')
-            return CanonPath(path);
+        if (isAbsolute(path))
+            return canonPath(path);
 
         throw Error("cannot fetch input '%s' because it uses a relative path", input.to_string());
     }
 
     std::pair<ref<SourceAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
     {
         Input input(_input);
-        std::string absPath;
         auto path = getStrAttr(input.attrs, "path");
 
-        if (path[0] != '/') {
-            if (!input.parent)
-                throw Error("cannot fetch input '%s' because it uses a relative path", input.to_string());
-
-            auto parent = canonPath(*input.parent);
-
-            // the path isn't relative, prefix it
-            absPath = nix::absPath(path, parent);
-
-            // for security, ensure that if the parent is a store path, it's inside it
-            if (store->isInStore(parent)) {
-                auto storePath = store->printStorePath(store->toStorePath(parent).first);
-                if (!isDirOrInDir(absPath, storePath))
-                    throw BadStorePath("relative path '%s' points outside of its parent's store path '%s'", path, storePath);
-            }
-        } else
-            absPath = path;
+        auto absPath = getAbsPath(input);
 
-        Activity act(*logger, lvlTalkative, actUnknown, fmt("copying '%s'", absPath));
+        Activity act(*logger, lvlTalkative, actUnknown, fmt("copying '%s' to the store", absPath));
 
         // FIXME: check whether access to 'path' is allowed.
-        auto storePath = store->maybeParseStorePath(absPath);
+        auto storePath = store->maybeParseStorePath(absPath.string());
 
         if (storePath)
             store->addTempRoot(*storePath);
@@ -154,7 +137,7 @@ struct PathInputScheme : InputScheme
         if (!storePath || storePath->name() != "source" || !store->isValidPath(*storePath)) {
             // FIXME: try to substitute storePath.
             auto src = sinkToSource([&](Sink & sink) {
-                mtime = dumpPathAndGetMtime(absPath, sink, defaultPathFilter);
+                mtime = dumpPathAndGetMtime(absPath.string(), sink, defaultPathFilter);
             });
             storePath = store->addToStoreFromDump(*src, "source");
         }
@@ -176,7 +159,7 @@ struct PathInputScheme : InputScheme
            store object and the subpath. */
         auto path = getAbsPath(input);
         try {
-            auto [storePath, subPath] = store->toStorePath(path.abs());
+            auto [storePath, subPath] = store->toStorePath(path.string());
             auto info = store->queryPathInfo(storePath);
             return fmt("path:%s:%s", info->narHash.to_string(HashFormat::Base16, false), subPath);
         } catch (Error &) {