From 6e2fcb7e2971561f526cbb332cb323a5d4def336 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Thu, 6 Feb 2025 16:31:42 +0100
Subject: [PATCH] Parser: Respect the accessor of the source file for relative
 paths

---
 src/libexpr/parser.y        | 15 +++++++++++----
 src/libflake/flake/flake.cc |  8 ++------
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 944c7b1af..bde721401 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -359,11 +359,18 @@ string_parts_interpolated
 
 path_start
   : PATH {
-    Path path(absPath(std::string_view{$1.p, $1.l}, state->basePath.path.abs()));
+    std::string_view literal({$1.p, $1.l});
+    Path path(absPath(literal, state->basePath.path.abs()));
     /* add back in the trailing '/' to the first segment */
-    if ($1.p[$1.l-1] == '/' && $1.l > 1)
-      path += "/";
-    $$ = new ExprPath(ref<SourceAccessor>(state->rootFS), std::move(path));
+    if (literal.size() > 1 && literal.back() == '/')
+      path += '/';
+    $$ =
+        /* Absolute paths are always interpreted relative to the
+           root filesystem accessor, rather than the accessor of the
+           current Nix expression. */
+        literal.front() == '/'
+        ? new ExprPath(state->rootFS, std::move(path))
+        : new ExprPath(state->basePath.accessor, std::move(path));
   }
   | HPATH {
     if (state->settings.pureEval) {
diff --git a/src/libflake/flake/flake.cc b/src/libflake/flake/flake.cc
index eee22d516..fcb04ac7f 100644
--- a/src/libflake/flake/flake.cc
+++ b/src/libflake/flake/flake.cc
@@ -186,9 +186,7 @@ static FlakeInput parseFlakeInput(
                     url = attr.value->string_view();
                 else if (attr.value->type() == nPath) {
                     auto path = attr.value->path();
-                    if (path.accessor != flakeDir.accessor
-                        // FIXME: hack necessary since the parser currently stores all paths as inside rootFS.
-                        && flakeDir.accessor == state.rootFS)
+                    if (path.accessor != flakeDir.accessor)
                         throw Error("input attribute path '%s' at %s must be in the same source tree as %s",
                             path, state.positions[attr.pos], flakeDir);
                     url = "path:" + flakeDir.path.makeRelative(path.path);
@@ -337,9 +335,7 @@ static Flake readFlake(
                     state.symbols[setting.name],
                     std::string(state.forceStringNoCtx(*setting.value, setting.pos, "")));
             else if (setting.value->type() == nPath) {
-                // FIXME: hack necessary since the parser currently stores all paths as inside rootFS.
-                SourcePath path(rootDir.accessor, setting.value->path().path);
-                auto storePath = fetchToStore(*state.store, path, FetchMode::Copy);
+                auto storePath = fetchToStore(*state.store, setting.value->path(), FetchMode::Copy);
                 flake.config.settings.emplace(
                     state.symbols[setting.name],
                     state.store->toRealPath(storePath));