flake: Fix follow symlinks

Contributes towards #106.

(cherry picked from commit 24d11d22c31dd7773cbcef6ea077e62ea114e2a3)
Upstream-PR: https://github.com/NixOS/nix/pull/12286
Change-Id: I523c76e31f27fac5d73eff76b22894adcd6ee135

doc/manual/change-authors.yml

@@ -247,6 +247,9 @@ roberth:
 seppel3210:
   github: Seppel3210
 
+stevalkr:
+  github: stevalkr
+
 teofilc:
   forgejo: teofilc
   github: TeofilC
@@ -288,6 +291,10 @@ xanderio:
 xokdvium:
   github: xokdvium
 
+xyenon:
+  forgejo: xyenon
+  github: xyenon
+
 yorickvp:
   github: yorickvp
 

doc/manual/rl-next/flake-follow-symlinks.md

@@ -0,0 +1,10 @@
+---
+synopsis: Fix resolving of symlinks in flake paths
+issues: [fj#106]
+prs: [12286]
+cls: [4783]
+category: Fixes
+credits: [stevalkr, xyenon]
+---
+
+Flake paths are now canonicalized to resolve symlinks. This ensures that when a flake is accessed via a symlink, paths are resolved relative to the target directory, not the symlink's location.

lix/libexpr/flake/flakeref.cc

@@ -7,6 +7,8 @@
 #include "lix/libfetchers/fetchers.hh"
 #include "lix/libfetchers/registry.hh"
 
+#include <cerrno>
+
 namespace nix {
 
 #if 0
@@ -150,6 +152,14 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
                         throw BadURL("could not find a flake.nix file");
                 }
 
+                try {
+                    path = absPath(path, std::nullopt, true);
+                } catch (SysError & e) {
+                    if (e.errNo != ENOENT && e.errNo != ENOTDIR) {
+                        throw;
+                    }
+                }
+
                 if (!S_ISDIR(lstat(path).st_mode))
                     throw BadURL("path '%s' is not a flake (because it's not a directory)", path);
 

tests/functional2/flakes/assets/flake1.nix

@@ -0,0 +1,7 @@
+{
+  outputs =
+    { self }:
+    {
+      x = 2;
+    };
+}

tests/functional2/flakes/assets/flake2.nix

@@ -0,0 +1,7 @@
+{
+  outputs =
+    { self }:
+    {
+      x = builtins.readFile ../file;
+    };
+}

tests/functional2/flakes/assets/flake_a.nix

@@ -0,0 +1,7 @@
+{
+  outputs =
+    { self }:
+    {
+      x = "a";
+    };
+}

tests/functional2/flakes/assets/flake_b.nix

@@ -0,0 +1,7 @@
+{
+  outputs =
+    { self }:
+    {
+      x = "b";
+    };
+}

tests/functional2/flakes/test_symlink_paths.py

@@ -0,0 +1,75 @@
+from pathlib import Path
+
+from functional2.testlib.fixtures.nix import Nix
+from functional2.testlib.fixtures.file_helper import CopyFile, Symlink, with_files, File
+from functional2.testlib.utils import get_global_asset_pack
+from functional2.testlib.fixtures.command import Command
+from functional2.testlib.fixtures.env import ManagedEnv
+
+
+@with_files(
+    {"flake1": {"flake.nix": CopyFile("assets/flake1.nix")}, "flake1_sym": Symlink("flake1")}
+)
+def test_symlink_points_to_flake(nix: Nix, files: Path) -> None:
+    result = nix.nix(["eval", f"{files}/flake1_sym#x"], flake=True).run().ok()
+    assert result.stdout_plain == "2"
+
+
+@with_files(
+    {
+        "subdir": {"flake1": {"flake.nix": CopyFile("assets/flake1.nix")}},
+        "subdir_sym": Symlink("subdir"),
+    }
+)
+def test_symlink_points_to_flake_in_subdir(nix: Nix, files: Path) -> None:
+    result = nix.nix(["eval", f"{files}/subdir_sym/flake1#x"], flake=True).run().ok()
+    assert result.stdout_plain == "2"
+
+
+@with_files(
+    {
+        "flake1": {"subdir": {"flake.nix": CopyFile("assets/flake1.nix")}},
+        "flake1_sym": Symlink("flake1/subdir"),
+    }
+)
+def test_symlink_points_to_dir_in_repo(nix: Nix, files: Path) -> None:
+    result = nix.nix(["eval", f"{files}/flake1_sym#x"], flake=True).run().ok()
+    assert result.stdout_plain == "2"
+
+
+@with_files(
+    {
+        "repo1": get_global_asset_pack(".git")
+        | {"file": File("Hello"), "subdir": {"flake.nix": CopyFile("assets/flake2.nix")}},
+        "repo2": get_global_asset_pack(".git")
+        | {"file": File("World"), "flake1_sym": Symlink("../repo1/subdir")},
+    }
+)
+def test_symlink_from_repo_to_another(nix: Nix, files: Path, env: ManagedEnv) -> None:
+    env.path.add_program("git")
+
+    Command(["git", "add", "subdir/flake.nix", "file"], _env=env, cwd=files / "repo1").run().ok()
+    result = nix.nix(["eval", f"{files}/repo1/subdir#x"], flake=True).run().ok()
+    assert result.stdout_plain == '"Hello"'
+
+    Command(["git", "add", "flake1_sym", "file"], _env=env, cwd=files / "repo2").run().ok()
+    result = nix.nix(["eval", f"{files}/repo2/flake1_sym#x"], flake=True).run().ok()
+    assert result.stdout_plain == '"Hello"'
+
+
+@with_files(
+    {
+        "repo1": get_global_asset_pack(".git")
+        | {"flake.nix": CopyFile("assets/flake_a.nix"), "subdir": {}},
+        "repo2": get_global_asset_pack(".git")
+        | {"flake.nix": CopyFile("assets/flake_b.nix"), "subdir_sym": Symlink("../repo1/subdir")},
+    }
+)
+def test_symlink_to_subdir_without_flake(nix: Nix, files: Path, env: ManagedEnv) -> None:
+    env.path.add_program("git")
+
+    Command(["git", "add", "flake.nix", "subdir"], _env=env, cwd=files / "repo1").run().ok()
+    Command(["git", "add", "flake.nix", "subdir_sym"], _env=env, cwd=files / "repo2").run().ok()
+
+    result = nix.nix(["eval", f"{files}/repo2/subdir_sym#x"], flake=True).run().ok()
+    assert result.stdout_plain == '"b"'