feat(tvix/glue): introduce test suite for context strings r/7404

This is an additional test suite on the top of the Nix ones
for context strings matters.

It already smoked out multiple mistakes and potential bugs and non-deterministic result from the evaluator.

It uses a similar technology as the one in the tvix-eval albeit we instantiate a fully fledged evaluator
with in-memory store.

We copy the files instead of symlinking them because crates are built in
isolation, so symlinks cannot work.

Change-Id: I63ae225ce4f83c6e2c8ccd60d779c2f8eb9d08fb
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10619
Autosubmit: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

2 files changed, 43 insertions, 0 deletions

diff --git a/tvix/glue/src/tests/nix_tests/notyetpassing/eval-okay-context-introspection.exp b/tvix/glue/src/tests/nix_tests/notyetpassing/eval-okay-context-introspection.exp
new file mode 100644
index 000000000000..03b400cc8862
--- /dev/null
+++ b/tvix/glue/src/tests/nix_tests/notyetpassing/eval-okay-context-introspection.exp
@@ -0,0 +1 @@
+[ true true true true true true ]
diff --git a/tvix/glue/src/tests/nix_tests/notyetpassing/eval-okay-context-introspection.nix b/tvix/glue/src/tests/nix_tests/notyetpassing/eval-okay-context-introspection.nix
new file mode 100644
index 000000000000..354376b89535
--- /dev/null
+++ b/tvix/glue/src/tests/nix_tests/notyetpassing/eval-okay-context-introspection.nix
@@ -0,0 +1,42 @@
+let
+  drv = derivation {
+    name = "fail";
+    builder = "/bin/false";
+    system = "x86_64-linux";
+    outputs = [ "out" "foo" ];
+  };
+
+  path = "${./eval-okay-context-introspection.nix}";
+
+  desired-context = {
+    "${builtins.unsafeDiscardStringContext path}" = {
+      path = true;
+    };
+    "${builtins.unsafeDiscardStringContext drv.drvPath}" = {
+      outputs = [ "foo" "out" ];
+      allOutputs = true;
+    };
+  };
+
+  combo-path = "${path}${drv.outPath}${drv.foo.outPath}${drv.drvPath}";
+  legit-context = builtins.getContext combo-path;
+
+  reconstructed-path = builtins.appendContext
+    (builtins.unsafeDiscardStringContext combo-path)
+    desired-context;
+
+  # Eta rule for strings with context.
+  etaRule = str:
+    str == builtins.appendContext
+      (builtins.unsafeDiscardStringContext str)
+      (builtins.getContext str);
+
+in
+[
+  (legit-context == desired-context)
+  (reconstructed-path == combo-path)
+  (etaRule "foo")
+  (etaRule drv.drvPath)
+  (etaRule drv.foo.outPath)
+  (etaRule (builtins.unsafeDiscardOutputDependency drv.drvPath))
+]