From 1e08e12d8138b09e6872cb498b723ade9ad71d68 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Fri, 25 Aug 2023 17:18:37 +0200
Subject: [PATCH] pathExists: isDir when endswith /

Fixes https://github.com/NixOS/nix/issues/8838
---
 src/libexpr/primops.cc              | 16 +++++++++++++---
 tests/lang/eval-okay-pathexists.nix |  1 +
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 283f99a48..915b872c8 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1520,15 +1520,25 @@ static RegisterPrimOp primop_storePath({
 
 static void prim_pathExists(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
+    auto & arg = *args[0];
+
     /* We don’t check the path right now, because we don’t want to
        throw if the path isn’t allowed, but just return false (and we
        can’t just catch the exception here because we still want to
-       throw if something in the evaluation of `*args[0]` tries to
+       throw if something in the evaluation of `arg` tries to
        access an unauthorized path). */
-    auto path = realisePath(state, pos, *args[0], { .checkForPureEval = false });
+    auto path = realisePath(state, pos, arg, { .checkForPureEval = false });
+
+    /* SourcePath doesn't know about trailing slash. */
+    auto mustBeDir = arg.type() == nString && arg.str().ends_with("/");
 
     try {
-        v.mkBool(state.checkSourcePath(path).pathExists());
+        auto checked = state.checkSourcePath(path);
+        auto exists = checked.pathExists();
+        if (exists && mustBeDir) {
+            exists = checked.lstat().type == InputAccessor::tDirectory;
+        }
+        v.mkBool(exists);
     } catch (SysError & e) {
         /* Don't give away info from errors while canonicalising
            ‘path’ in restricted mode. */
diff --git a/tests/lang/eval-okay-pathexists.nix b/tests/lang/eval-okay-pathexists.nix
index 8eae37e70..e1246e370 100644
--- a/tests/lang/eval-okay-pathexists.nix
+++ b/tests/lang/eval-okay-pathexists.nix
@@ -1,6 +1,7 @@
 builtins.pathExists (./lib.nix)
 && builtins.pathExists (builtins.toPath ./lib.nix)
 && builtins.pathExists (builtins.toString ./lib.nix)
+&& !builtins.pathExists (builtins.toString ./lib.nix + "/")
 && builtins.pathExists (builtins.toPath (builtins.toString ./lib.nix))
 && !builtins.pathExists (builtins.toPath (builtins.toString ./bla.nix))
 && builtins.pathExists ./lib.nix