Improve support for relative path inputs

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

@@ -159,6 +159,12 @@ 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().
      */
@@ -95,6 +90,12 @@ public:
      */
     bool isLocked() 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
@@ -260,6 +261,9 @@ 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

@@ -94,7 +94,7 @@ struct PathInputScheme : InputScheme
         writeFile((CanonPath(getAbsPath(input)) / path).abs(), 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 (hasPrefix(path, "/"))
@@ -121,31 +121,14 @@ struct PathInputScheme : InputScheme
     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 absPath = getAbsPath(input);
 
-            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;
-
-        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.abs());
 
         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.abs(), sink, defaultPathFilter);
             });
             storePath = store->addToStoreFromDump(*src, "source");
         }