From beb7f57c73473598c51b14221c5e4996c81d2dde Mon Sep 17 00:00:00 2001
From: binarycat <binarycat@envs.net>
Date: Sun, 2 Jun 2024 19:58:54 +0200
Subject: [PATCH] fix(tvix/eval): handle builtins.split matching the empty
 string

This prevents the following statements from looping endlessly:

```
builtins.split "(.*)" ""
builtins.split "([abc]*)" "abc"
builtins.split "(.*)" "abc"
builtins.split ".*" ""
```

Cover these (and some more examples) in the test suite.

Co-Authored-By: Florian Klink <flokli@flokli.de>
Change-Id: Ibd339f971e0f4e3e5c229816e2be5a8e3836fec9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11743
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
---
 tvix/eval/src/builtins/mod.rs                          |  3 +++
 .../src/tests/tvix_tests/eval-okay-builtins-split.exp  |  1 +
 .../src/tests/tvix_tests/eval-okay-builtins-split.nix  | 10 ++++++++++
 .../tvix_tests/eval-okay-context-introspection.nix     |  2 +-
 4 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 tvix/eval/src/tests/tvix_tests/eval-okay-builtins-split.exp
 create mode 100644 tvix/eval/src/tests/tvix_tests/eval-okay-builtins-split.nix

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index 5cd94bcf3..8fc80b2f9 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -1286,6 +1286,9 @@ mod pure_builtins {
                 })
                 .collect();
             ret.push_back(Value::List(NixList::from(v)));
+            if pos == text.len() {
+                break;
+            }
             pos = thematch.end();
         }
 
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-split.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-split.exp
new file mode 100644
index 000000000..eb2117a0c
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-split.exp
@@ -0,0 +1 @@
+[ [ "" [ "a" ] "c" ] [ "" [ "a" ] "b" [ "c" ] "" ] [ "" [ "a" null ] "b" [ null "c" ] "" ] [ " " [ "FOO" ] " " ] [ "" [ "abc" ] "" [ "" ] "" ] [ "" [ "abc" ] "" [ "" ] "" ] [ "" [ ] "" ] ]
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-split.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-split.nix
new file mode 100644
index 000000000..95305040d
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-split.nix
@@ -0,0 +1,10 @@
+[
+  (builtins.split "(a)b" "abc")
+  (builtins.split "([ac])" "abc")
+  (builtins.split "(a)|(c)" "abc")
+  (builtins.split "([[:upper:]]+)" " FOO ")
+
+  (builtins.split "(.*)" "abc")
+  (builtins.split "([abc]*)" "abc")
+  (builtins.split ".*" "")
+]
diff --git a/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.nix b/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.nix
index ecd8ab007..e5719e00c 100644
--- a/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.nix
+++ b/tvix/glue/src/tests/tvix_tests/eval-okay-context-introspection.nix
@@ -71,7 +71,7 @@ in
   (builtins.hasAttr "allOutputs" (builtins.getContext drv.drvPath)."${builtins.unsafeDiscardStringContext drv.drvPath}")
   (legit-context == desired-context) # FIXME(raitobezarius): this should not use `builtins.seq`, this is a consequence of excessive laziness of Tvix, I believe.
   (reconstructed-path == combo-path)
-  # Those are too slow?
+  # These still fail with an internal error
   # (etaRule' "foo")
   # (etaRule' combo-path)
   (etaRule "foo")