From 6837c95268bd0b7c0d672faddaf1681f07da292b Mon Sep 17 00:00:00 2001
From: Alex Ivliev <Alex.Ivliev@mailbox.tu-dresden.de>
Date: Tue, 2 Apr 2024 10:12:59 +0200
Subject: [PATCH] Bug/428 (#459)

* Fix #428 by considering subtraction of zero column tries to be empty

---------

Co-authored-by: Alex Ivliev <alex.ivliev@tu-dresden.de>
---
 nemo-physical/src/tabular/operations/subtract.rs  |  5 +++++
 .../testcases/regression/unbound_negation/run.rls | 15 +++++++++++++++
 .../unbound_negation/run/NonNegative.csv          |  0
 .../unbound_negation/run/NonPositive.csv          |  1 +
 4 files changed, 21 insertions(+)
 create mode 100644 resources/testcases/regression/unbound_negation/run.rls
 create mode 100644 resources/testcases/regression/unbound_negation/run/NonNegative.csv
 create mode 100644 resources/testcases/regression/unbound_negation/run/NonPositive.csv

diff --git a/nemo-physical/src/tabular/operations/subtract.rs b/nemo-physical/src/tabular/operations/subtract.rs
index e4c0b7675..ac2906f27 100644
--- a/nemo-physical/src/tabular/operations/subtract.rs
+++ b/nemo-physical/src/tabular/operations/subtract.rs
@@ -76,6 +76,11 @@ impl OperationGenerator for GeneratorSubtract {
             return None;
         }
 
+        if tries_subtract.iter().any(|scan| scan.arity() == 0) {
+            // If we subtract a non empty zero column trie the result is defined as empty
+            return None;
+        }
+
         let mut active_scans = Vec::with_capacity(trie_main.arity() + 1);
         active_scans.push(Rc::new(RefCell::new(vec![true; tries_subtract.len()])));
 
diff --git a/resources/testcases/regression/unbound_negation/run.rls b/resources/testcases/regression/unbound_negation/run.rls
new file mode 100644
index 000000000..d4c1e4273
--- /dev/null
+++ b/resources/testcases/regression/unbound_negation/run.rls
@@ -0,0 +1,15 @@
+%%% Test related to 
+%%% https://github.com/knowsys/nemo/issues/428
+%%%
+%%% Previously, subtracting a zero arity table resulted in a crash 
+
+Input(-1).
+
+Assert(positive) :- Input(?i), ?i > 0.
+Assert(negative) :- Input(?i), ?i < 0.
+
+NonPositive(?r) :- Input(?r), ~Assert(positive).
+NonNegative(?r) :- Input(?r), ~Assert(negative). 
+
+@export NonPositive :- csv {} .
+@export NonNegative :- csv {} .
\ No newline at end of file
diff --git a/resources/testcases/regression/unbound_negation/run/NonNegative.csv b/resources/testcases/regression/unbound_negation/run/NonNegative.csv
new file mode 100644
index 000000000..e69de29bb
diff --git a/resources/testcases/regression/unbound_negation/run/NonPositive.csv b/resources/testcases/regression/unbound_negation/run/NonPositive.csv
new file mode 100644
index 000000000..d7d17fcbe
--- /dev/null
+++ b/resources/testcases/regression/unbound_negation/run/NonPositive.csv
@@ -0,0 +1 @@
+-1
\ No newline at end of file