From 42c59b1276e1ad6e0800529a345a0602da216330 Mon Sep 17 00:00:00 2001
From: Stephan Renatus <stephan.renatus@gmail.com>
Date: Fri, 28 May 2021 15:13:19 +0200
Subject: [PATCH] topdown: deal with default functions (#3505)

They aren't supported, but they can lead to a situation where
ir.Empty() is false, but ir.Rules still has length 0.

Signed-off-by: Stephan Renatus <stephan.renatus@gmail.com>
---
 internal/wasm/sdk/test/e2e/exceptions.yaml    |  1 +
 .../functions/test-functions-default.yaml     | 21 +++++++++++++++++++
 .../functions/test-functions-unused-arg.yaml  |  2 +-
 topdown/eval.go                               |  4 +++-
 4 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 test/cases/testdata/functions/test-functions-default.yaml

diff --git a/internal/wasm/sdk/test/e2e/exceptions.yaml b/internal/wasm/sdk/test/e2e/exceptions.yaml
index 8c3413b8c6..371d791a76 100644
--- a/internal/wasm/sdk/test/e2e/exceptions.yaml
+++ b/internal/wasm/sdk/test/e2e/exceptions.yaml
@@ -1 +1,2 @@
 # Exception Format is <test name>: <reason>
+"functions/default": "not supported in topdown, https://github.com/open-policy-agent/opa/issues/2445"
\ No newline at end of file
diff --git a/test/cases/testdata/functions/test-functions-default.yaml b/test/cases/testdata/functions/test-functions-default.yaml
new file mode 100644
index 0000000000..00c7abcd29
--- /dev/null
+++ b/test/cases/testdata/functions/test-functions-default.yaml
@@ -0,0 +1,21 @@
+cases:
+- data:
+  modules:
+  - |
+    package p.m
+
+    default hello = false
+
+    hello() = m {
+      m = input.message
+      1 == 2
+      m = "world"
+    }
+    h = m {
+      m = hello()
+    }
+  note: functions/default # not supported but shouldn't panic
+  query: data.p.m = x
+  want_result:
+  - x:
+      hello: false
diff --git a/test/cases/testdata/functions/test-functions-unused-arg.yaml b/test/cases/testdata/functions/test-functions-unused-arg.yaml
index 2d28050574..705984509d 100644
--- a/test/cases/testdata/functions/test-functions-unused-arg.yaml
+++ b/test/cases/testdata/functions/test-functions-unused-arg.yaml
@@ -7,6 +7,6 @@ cases:
     f(x) {
         r = input.that_is_not_there
     }
-  note: basic call
+  note: unused arg
   query: data.p.f(1)
   want_result: []
diff --git a/topdown/eval.go b/topdown/eval.go
index 54791c4f6c..9b8fabe5ce 100644
--- a/topdown/eval.go
+++ b/topdown/eval.go
@@ -1506,7 +1506,9 @@ func (e evalFunc) eval(iter unifyIterator) error {
 		return err
 	}
 
-	if ir.Empty() {
+	// default functions aren't supported:
+	// https://github.com/open-policy-agent/opa/issues/2445
+	if len(ir.Rules) == 0 {
 		return nil
 	}