feat(tvix/glue): add some import tests r/7212

This creates a directory with a .keep file inside, and uses
"${path/to/there}" to coerce it to a string (and import it into the
store), ensuring it calculates the same store paths as Nix does.

Change-Id: Ie14ae075104ce278bc4f2cce93aab5762a2734d1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10343
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

4 files changed, 301 insertions, 42 deletions

diff --git a/tvix/Cargo.lock b/tvix/Cargo.lock
index 1df6d199a541..9a0f051933c2 100644
--- a/tvix/Cargo.lock
+++ b/tvix/Cargo.lock
@@ -794,12 +794,9 @@ dependencies = [
 
 [[package]]
 name = "fastrand"
-version = "1.9.0"
+version = "2.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e51093e27b0797c359783294ca4f0a911c270184cb10f85783b118614a1501be"
-dependencies = [
- "instant",
-]
+checksum = "25cbce373ec4653f1a01a31e8a5e5ec0c622dc27ff9c4e6606eefef5cbbed4a5"
 
 [[package]]
 name = "fd-lock"
@@ -808,7 +805,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "39ae6b3d9530211fb3b12a95374b8b0823be812f53d09e18c5675c0146b09642"
 dependencies = [
  "cfg-if",
- "rustix",
+ "rustix 0.37.19",
  "windows-sys 0.48.0",
 ]
 
@@ -1236,7 +1233,7 @@ checksum = "adcf93614601c8129ddf72e2d5633df827ba6551541c6d8c59520a371475be1f"
 dependencies = [
  "hermit-abi 0.3.1",
  "io-lifetimes",
- "rustix",
+ "rustix 0.37.19",
  "windows-sys 0.48.0",
 ]
 
@@ -1362,6 +1359,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ece97ea872ece730aed82664c424eb4c8291e1ff2480247ccf7409044bc6479f"
 
 [[package]]
+name = "linux-raw-sys"
+version = "0.4.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c4cd1a83af159aa67994778be9070f0ae1bd732942279cabb14f86f986a21456"
+
+[[package]]
 name = "litrs"
 version = "0.2.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2035,6 +2038,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "redox_syscall"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4722d768eff46b75989dd134e5c353f0d6296e5aaa3132e776cbdb56be7731aa"
+dependencies = [
+ "bitflags 1.3.2",
+]
+
+[[package]]
 name = "redox_users"
 version = "0.4.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2178,7 +2190,20 @@ dependencies = [
  "errno",
  "io-lifetimes",
  "libc",
- "linux-raw-sys",
+ "linux-raw-sys 0.3.7",
+ "windows-sys 0.48.0",
+]
+
+[[package]]
+name = "rustix"
+version = "0.38.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b426b0506e5d50a7d8dafcf2e81471400deb602392c7dd110815afb4eaf02a3"
+dependencies = [
+ "bitflags 2.4.1",
+ "errno",
+ "libc",
+ "linux-raw-sys 0.4.12",
  "windows-sys 0.48.0",
 ]
 
@@ -2619,15 +2644,15 @@ dependencies = [
 
 [[package]]
 name = "tempfile"
-version = "3.5.0"
+version = "3.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b9fbec84f381d5795b08656e4912bec604d162bff9291d6189a78f4c8ab87998"
+checksum = "7ef1adac450ad7f4b3c28589471ade84f25f731a7a0fe30d71dfa9f60fd808e5"
 dependencies = [
  "cfg-if",
  "fastrand",
- "redox_syscall 0.3.5",
- "rustix",
- "windows-sys 0.45.0",
+ "redox_syscall 0.4.1",
+ "rustix 0.38.21",
+ "windows-sys 0.48.0",
 ]
 
 [[package]]
@@ -3164,6 +3189,7 @@ dependencies = [
  "criterion",
  "lazy_static",
  "nix-compat",
+ "tempfile",
  "test-case",
  "thiserror",
  "tokio",
diff --git a/tvix/Cargo.nix b/tvix/Cargo.nix
index 91709258ef55..c7957403e2d5 100644
--- a/tvix/Cargo.nix
+++ b/tvix/Cargo.nix
@@ -879,6 +879,7 @@ rec {
           "rustc-dep-of-std" = [ "core" "compiler_builtins" ];
           "serde" = [ "dep:serde" ];
         };
+        resolvedDefaultFeatures = [ "std" ];
       };
       "bitmaps" = rec {
         crateName = "bitmaps";
@@ -2283,6 +2284,7 @@ rec {
         features = {
           "default" = [ "std" ];
         };
+        resolvedDefaultFeatures = [ "std" ];
       };
       "errno-dragonfly" = rec {
         crateName = "errno-dragonfly";
@@ -2330,28 +2332,19 @@ rec {
       };
       "fastrand" = rec {
         crateName = "fastrand";
-        version = "1.9.0";
+        version = "2.0.1";
         edition = "2018";
-        sha256 = "1gh12m56265ihdbzh46bhh0jf74i197wm51jg1cw75q7ggi96475";
+        sha256 = "19flpv5zbzpf0rk4x77z4zf25in0brg8l7m304d3yrf47qvwxjr5";
         authors = [
           "Stjepan Glavina <stjepang@gmail.com>"
         ];
-        dependencies = [
-          {
-            name = "instant";
-            packageId = "instant";
-            target = { target, features }: (("wasm32" == target."arch" or null) && (!("wasi" == target."os" or null)));
-          }
-        ];
-        devDependencies = [
-          {
-            name = "instant";
-            packageId = "instant";
-            target = { target, features }: (("wasm32" == target."arch" or null) && (!("wasi" == target."os" or null)));
-            features = [ "wasm-bindgen" ];
-          }
-        ];
-
+        features = {
+          "default" = [ "std" ];
+          "getrandom" = [ "dep:getrandom" ];
+          "js" = [ "std" "getrandom" ];
+          "std" = [ "alloc" ];
+        };
+        resolvedDefaultFeatures = [ "alloc" "default" "std" ];
       };
       "fd-lock" = rec {
         crateName = "fd-lock";
@@ -2368,7 +2361,7 @@ rec {
           }
           {
             name = "rustix";
-            packageId = "rustix";
+            packageId = "rustix 0.37.19";
             target = { target, features }: (target."unix" or false);
             features = [ "fs" ];
           }
@@ -3761,7 +3754,7 @@ rec {
           }
           {
             name = "rustix";
-            packageId = "rustix";
+            packageId = "rustix 0.37.19";
             target = { target, features }: (!((target."windows" or false) || ("hermit" == target."os" or null) || ("unknown" == target."os" or null)));
             features = [ "termios" ];
           }
@@ -4113,7 +4106,7 @@ rec {
         };
         resolvedDefaultFeatures = [ "default" ];
       };
-      "linux-raw-sys" = rec {
+      "linux-raw-sys 0.3.7" = rec {
         crateName = "linux-raw-sys";
         version = "0.3.7";
         edition = "2018";
@@ -4129,6 +4122,22 @@ rec {
         };
         resolvedDefaultFeatures = [ "errno" "general" "ioctl" "no_std" ];
       };
+      "linux-raw-sys 0.4.12" = rec {
+        crateName = "linux-raw-sys";
+        version = "0.4.12";
+        edition = "2021";
+        sha256 = "0mhlla3gk1jgn6mrq9s255rvvq8a1w3yk2vpjiwsd6hmmy1imkf4";
+        authors = [
+          "Dan Gohman <dev@sunfishcode.online>"
+        ];
+        features = {
+          "compiler_builtins" = [ "dep:compiler_builtins" ];
+          "core" = [ "dep:core" ];
+          "default" = [ "std" "general" "errno" ];
+          "rustc-dep-of-std" = [ "core" "compiler_builtins" "no_std" ];
+        };
+        resolvedDefaultFeatures = [ "elf" "errno" "general" "ioctl" "no_std" ];
+      };
       "litrs" = rec {
         crateName = "litrs";
         version = "0.2.3";
@@ -6007,6 +6016,26 @@ rec {
           "rustc-dep-of-std" = [ "core" "bitflags/rustc-dep-of-std" ];
         };
       };
+      "redox_syscall 0.4.1" = rec {
+        crateName = "redox_syscall";
+        version = "0.4.1";
+        edition = "2018";
+        sha256 = "1aiifyz5dnybfvkk4cdab9p2kmphag1yad6iknc7aszlxxldf8j7";
+        libName = "syscall";
+        authors = [
+          "Jeremy Soller <jackpot51@gmail.com>"
+        ];
+        dependencies = [
+          {
+            name = "bitflags";
+            packageId = "bitflags 1.3.2";
+          }
+        ];
+        features = {
+          "core" = [ "dep:core" ];
+          "rustc-dep-of-std" = [ "core" "bitflags/rustc-dep-of-std" ];
+        };
+      };
       "redox_users" = rec {
         crateName = "redox_users";
         version = "0.4.3";
@@ -6580,7 +6609,7 @@ rec {
         ];
 
       };
-      "rustix" = rec {
+      "rustix 0.37.19" = rec {
         crateName = "rustix";
         version = "0.37.19";
         edition = "2018";
@@ -6638,14 +6667,14 @@ rec {
           }
           {
             name = "linux-raw-sys";
-            packageId = "linux-raw-sys";
+            packageId = "linux-raw-sys 0.3.7";
             usesDefaultFeatures = false;
             target = { target, features }: ((("android" == target."os" or null) || ("linux" == target."os" or null)) && ((target."rustix_use_libc" or false) || (target."miri" or false) || (!(("linux" == target."os" or null) && (("x86" == target."arch" or null) || (("x86_64" == target."arch" or null) && ("64" == target."pointer_width" or null)) || (("little" == target."endian" or null) && (("arm" == target."arch" or null) || (("aarch64" == target."arch" or null) && ("64" == target."pointer_width" or null)) || ("powerpc64" == target."arch" or null) || ("riscv64" == target."arch" or null) || ("mips" == target."arch" or null) || ("mips64" == target."arch" or null))))))));
             features = [ "general" "ioctl" "no_std" ];
           }
           {
             name = "linux-raw-sys";
-            packageId = "linux-raw-sys";
+            packageId = "linux-raw-sys 0.3.7";
             usesDefaultFeatures = false;
             target = { target, features }: ((!(target."rustix_use_libc" or false)) && (!(target."miri" or false)) && ("linux" == target."os" or null) && (("x86" == target."arch" or null) || (("x86_64" == target."arch" or null) && ("64" == target."pointer_width" or null)) || (("little" == target."endian" or null) && (("arm" == target."arch" or null) || (("aarch64" == target."arch" or null) && ("64" == target."pointer_width" or null)) || ("powerpc64" == target."arch" or null) || ("riscv64" == target."arch" or null) || ("mips" == target."arch" or null) || ("mips64" == target."arch" or null)))));
             features = [ "general" "errno" "ioctl" "no_std" ];
@@ -6701,6 +6730,115 @@ rec {
         };
         resolvedDefaultFeatures = [ "default" "fs" "io-lifetimes" "libc" "std" "termios" "use-libc-auxv" ];
       };
+      "rustix 0.38.21" = rec {
+        crateName = "rustix";
+        version = "0.38.21";
+        edition = "2021";
+        sha256 = "18q2mx7gnnl1238psb1r0avdw00l8y0jxkxgimyhmmg50q2nnhib";
+        authors = [
+          "Dan Gohman <dev@sunfishcode.online>"
+          "Jakub Konka <kubkon@jakubkonka.com>"
+        ];
+        dependencies = [
+          {
+            name = "bitflags";
+            packageId = "bitflags 2.4.1";
+            usesDefaultFeatures = false;
+          }
+          {
+            name = "errno";
+            packageId = "errno";
+            rename = "libc_errno";
+            optional = true;
+            usesDefaultFeatures = false;
+            target = { target, features }: ((!(target."rustix_use_libc" or false)) && (!(target."miri" or false)) && ("linux" == target."os" or null) && ("little" == target."endian" or null) && (("arm" == target."arch" or null) || (("aarch64" == target."arch" or null) && ("64" == target."pointer_width" or null)) || ("riscv64" == target."arch" or null) || ((target."rustix_use_experimental_asm" or false) && ("powerpc64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips32r6" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64r6" == target."arch" or null)) || ("x86" == target."arch" or null) || (("x86_64" == target."arch" or null) && ("64" == target."pointer_width" or null))));
+          }
+          {
+            name = "errno";
+            packageId = "errno";
+            rename = "libc_errno";
+            usesDefaultFeatures = false;
+            target = { target, features }: ((!(target."windows" or false)) && ((target."rustix_use_libc" or false) || (target."miri" or false) || (!(("linux" == target."os" or null) && ("little" == target."endian" or null) && (("arm" == target."arch" or null) || (("aarch64" == target."arch" or null) && ("64" == target."pointer_width" or null)) || ("riscv64" == target."arch" or null) || ((target."rustix_use_experimental_asm" or false) && ("powerpc64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips32r6" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64r6" == target."arch" or null)) || ("x86" == target."arch" or null) || (("x86_64" == target."arch" or null) && ("64" == target."pointer_width" or null)))))));
+          }
+          {
+            name = "errno";
+            packageId = "errno";
+            rename = "libc_errno";
+            usesDefaultFeatures = false;
+            target = { target, features }: (target."windows" or false);
+          }
+          {
+            name = "libc";
+            packageId = "libc";
+            optional = true;
+            usesDefaultFeatures = false;
+            target = { target, features }: ((!(target."rustix_use_libc" or false)) && (!(target."miri" or false)) && ("linux" == target."os" or null) && ("little" == target."endian" or null) && (("arm" == target."arch" or null) || (("aarch64" == target."arch" or null) && ("64" == target."pointer_width" or null)) || ("riscv64" == target."arch" or null) || ((target."rustix_use_experimental_asm" or false) && ("powerpc64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips32r6" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64r6" == target."arch" or null)) || ("x86" == target."arch" or null) || (("x86_64" == target."arch" or null) && ("64" == target."pointer_width" or null))));
+            features = [ "extra_traits" ];
+          }
+          {
+            name = "libc";
+            packageId = "libc";
+            usesDefaultFeatures = false;
+            target = { target, features }: ((!(target."windows" or false)) && ((target."rustix_use_libc" or false) || (target."miri" or false) || (!(("linux" == target."os" or null) && ("little" == target."endian" or null) && (("arm" == target."arch" or null) || (("aarch64" == target."arch" or null) && ("64" == target."pointer_width" or null)) || ("riscv64" == target."arch" or null) || ((target."rustix_use_experimental_asm" or false) && ("powerpc64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips32r6" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64r6" == target."arch" or null)) || ("x86" == target."arch" or null) || (("x86_64" == target."arch" or null) && ("64" == target."pointer_width" or null)))))));
+            features = [ "extra_traits" ];
+          }
+          {
+            name = "linux-raw-sys";
+            packageId = "linux-raw-sys 0.4.12";
+            usesDefaultFeatures = false;
+            target = { target, features }: ((("android" == target."os" or null) || ("linux" == target."os" or null)) && ((target."rustix_use_libc" or false) || (target."miri" or false) || (!(("linux" == target."os" or null) && ("little" == target."endian" or null) && (("arm" == target."arch" or null) || (("aarch64" == target."arch" or null) && ("64" == target."pointer_width" or null)) || ("riscv64" == target."arch" or null) || ((target."rustix_use_experimental_asm" or false) && ("powerpc64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips32r6" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64r6" == target."arch" or null)) || ("x86" == target."arch" or null) || (("x86_64" == target."arch" or null) && ("64" == target."pointer_width" or null)))))));
+            features = [ "general" "ioctl" "no_std" ];
+          }
+          {
+            name = "linux-raw-sys";
+            packageId = "linux-raw-sys 0.4.12";
+            usesDefaultFeatures = false;
+            target = { target, features }: ((!(target."rustix_use_libc" or false)) && (!(target."miri" or false)) && ("linux" == target."os" or null) && ("little" == target."endian" or null) && (("arm" == target."arch" or null) || (("aarch64" == target."arch" or null) && ("64" == target."pointer_width" or null)) || ("riscv64" == target."arch" or null) || ((target."rustix_use_experimental_asm" or false) && ("powerpc64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips32r6" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64" == target."arch" or null)) || ((target."rustix_use_experimental_asm" or false) && ("mips64r6" == target."arch" or null)) || ("x86" == target."arch" or null) || (("x86_64" == target."arch" or null) && ("64" == target."pointer_width" or null))));
+            features = [ "general" "errno" "ioctl" "no_std" "elf" ];
+          }
+          {
+            name = "windows-sys";
+            packageId = "windows-sys 0.48.0";
+            target = { target, features }: (target."windows" or false);
+            features = [ "Win32_Foundation" "Win32_Networking_WinSock" "Win32_NetworkManagement_IpHelper" "Win32_System_Threading" ];
+          }
+        ];
+        devDependencies = [
+          {
+            name = "errno";
+            packageId = "errno";
+            rename = "libc_errno";
+            usesDefaultFeatures = false;
+          }
+          {
+            name = "libc";
+            packageId = "libc";
+          }
+        ];
+        features = {
+          "all-apis" = [ "event" "fs" "io_uring" "mm" "mount" "net" "param" "pipe" "process" "procfs" "pty" "rand" "runtime" "shm" "stdio" "system" "termios" "thread" "time" ];
+          "default" = [ "std" "use-libc-auxv" ];
+          "io_uring" = [ "event" "fs" "net" "linux-raw-sys/io_uring" ];
+          "itoa" = [ "dep:itoa" ];
+          "libc" = [ "dep:libc" ];
+          "libc_errno" = [ "dep:libc_errno" ];
+          "linux_latest" = [ "linux_4_11" ];
+          "net" = [ "linux-raw-sys/net" "linux-raw-sys/netlink" "linux-raw-sys/if_ether" ];
+          "once_cell" = [ "dep:once_cell" ];
+          "param" = [ "fs" ];
+          "process" = [ "linux-raw-sys/prctl" ];
+          "procfs" = [ "once_cell" "itoa" "fs" ];
+          "pty" = [ "itoa" "fs" ];
+          "runtime" = [ "linux-raw-sys/prctl" ];
+          "rustc-dep-of-std" = [ "dep:core" "dep:alloc" "dep:compiler_builtins" "linux-raw-sys/rustc-dep-of-std" "bitflags/rustc-dep-of-std" "compiler_builtins?/rustc-dep-of-std" ];
+          "shm" = [ "fs" ];
+          "std" = [ "bitflags/std" "alloc" "libc?/std" "libc_errno?/std" ];
+          "system" = [ "linux-raw-sys/system" ];
+          "thread" = [ "linux-raw-sys/prctl" ];
+          "use-libc" = [ "libc_errno" "libc" ];
+        };
+        resolvedDefaultFeatures = [ "alloc" "default" "fs" "std" "use-libc-auxv" ];
+      };
       "rustls" = rec {
         crateName = "rustls";
         version = "0.21.7";
@@ -7878,9 +8016,9 @@ rec {
       };
       "tempfile" = rec {
         crateName = "tempfile";
-        version = "3.5.0";
+        version = "3.8.1";
         edition = "2018";
-        sha256 = "163rp254r3x7i5hisagrpxid2166pq94jvk511dpkmc1yf2fryxr";
+        sha256 = "1r88v07zdafzf46y63vs39rmzwl4vqd4g2c5qarz9mqa8nnavwby";
         authors = [
           "Steven Allen <steven@stebalien.com>"
           "The Rust Project Developers"
@@ -7898,18 +8036,18 @@ rec {
           }
           {
             name = "redox_syscall";
-            packageId = "redox_syscall 0.3.5";
+            packageId = "redox_syscall 0.4.1";
             target = { target, features }: ("redox" == target."os" or null);
           }
           {
             name = "rustix";
-            packageId = "rustix";
+            packageId = "rustix 0.38.21";
             target = { target, features }: ((target."unix" or false) || ("wasi" == target."os" or null));
             features = [ "fs" ];
           }
           {
             name = "windows-sys";
-            packageId = "windows-sys 0.45.0";
+            packageId = "windows-sys 0.48.0";
             target = { target, features }: (target."windows" or false);
             features = [ "Win32_Storage_FileSystem" "Win32_Foundation" ];
           }
@@ -9850,6 +9988,10 @@ rec {
             packageId = "lazy_static";
           }
           {
+            name = "tempfile";
+            packageId = "tempfile";
+          }
+          {
             name = "test-case";
             packageId = "test-case";
           }
diff --git a/tvix/glue/Cargo.toml b/tvix/glue/Cargo.toml
index 90ad2752691d..b0902b5c9983 100644
--- a/tvix/glue/Cargo.toml
+++ b/tvix/glue/Cargo.toml
@@ -20,6 +20,7 @@ git = "https://github.com/tvlfyi/wu-manber.git"
 [dev-dependencies]
 criterion = { version = "0.5", features = ["html_reports"] }
 lazy_static = "1.4.0"
+tempfile = "3.8.1"
 test-case = "2.2.2"
 
 [[bench]]
diff --git a/tvix/glue/src/tvix_store_io.rs b/tvix/glue/src/tvix_store_io.rs
index 31a472fed21c..325e11e97397 100644
--- a/tvix/glue/src/tvix_store_io.rs
+++ b/tvix/glue/src/tvix_store_io.rs
@@ -357,3 +357,93 @@ async fn import_path_with_pathinfo(
 
     Ok(path_info)
 }
+
+#[cfg(test)]
+mod tests {
+    use std::{cell::RefCell, path::Path, rc::Rc, sync::Arc};
+
+    use tempfile::TempDir;
+    use tvix_castore::{blobservice::MemoryBlobService, directoryservice::MemoryDirectoryService};
+    use tvix_eval::EvaluationResult;
+    use tvix_store::pathinfoservice::MemoryPathInfoService;
+
+    use crate::{builtins::add_derivation_builtins, known_paths::KnownPaths};
+
+    use super::TvixStoreIO;
+
+    /// evaluates a given nix expression and returns the result.
+    /// Takes care of setting up the evaluator so it knows about the
+    // `derivation` builtin.
+    fn eval(str: &str) -> EvaluationResult {
+        let mut eval = tvix_eval::Evaluation::new_impure(str, None);
+
+        let blob_service = Arc::new(MemoryBlobService::default());
+        let directory_service = Arc::new(MemoryDirectoryService::default());
+        let path_info_service = Arc::new(MemoryPathInfoService::new(
+            blob_service.clone(),
+            directory_service.clone(),
+        ));
+        let runtime = tokio::runtime::Runtime::new().unwrap();
+
+        eval.io_handle = Box::new(TvixStoreIO::new(
+            blob_service,
+            directory_service,
+            path_info_service,
+            runtime.handle().clone(),
+        ));
+
+        let known_paths: Rc<RefCell<KnownPaths>> = Default::default();
+
+        add_derivation_builtins(&mut eval, known_paths.clone());
+
+        // run the evaluation itself.
+        eval.evaluate()
+    }
+
+    /// Helper function that takes a &Path, and invokes a tvix evaluator coercing that path to a string
+    /// (via "${/this/path}"). The path can be both absolute or not.
+    /// It returns Option<String>, depending on whether the evaluation succeeded or not.
+    fn import_path_and_compare<P: AsRef<Path>>(p: P) -> Option<String> {
+        // Try to import the path using "${/tmp/path/to/test}".
+        // The format string looks funny, the {} passed to Nix needs to be
+        // escaped.
+        let code = format!(r#""${{{}}}""#, p.as_ref().display());
+        let result = eval(&code);
+
+        if !result.errors.is_empty() {
+            return None;
+        }
+
+        let value = result.value.expect("must be some");
+        match value {
+            tvix_eval::Value::String(s) => return Some(s.as_str().to_owned()),
+            _ => panic!("unexpected value type: {:?}", value),
+        }
+    }
+
+    /// Import a directory with a zero-sized ".keep" regular file.
+    /// Ensure it matches the (pre-recorded) store path that Nix would produce.
+    #[test]
+    fn import_directory() {
+        let tmpdir = TempDir::new().unwrap();
+
+        // create a directory named "test"
+        let src_path = tmpdir.path().join("test");
+        std::fs::create_dir(&src_path).unwrap();
+
+        // write a regular file `.keep`.
+        std::fs::write(src_path.join(".keep"), vec![]).unwrap();
+
+        // importing the path with .../test at the end.
+        assert_eq!(
+            Some("/nix/store/gq3xcv4xrj4yr64dflyr38acbibv3rm9-test".to_string()),
+            import_path_and_compare(&src_path)
+        );
+
+        // importing the path with .../test/. at the end.
+        assert_eq!(
+            Some("/nix/store/gq3xcv4xrj4yr64dflyr38acbibv3rm9-test".to_string()),
+            import_path_and_compare(src_path.join("."))
+        );
+    }
+}