fix: Issues #302, #303 (#304)

Handle undefined values correctly in ordered-else. Previously an undefined value
in one of the blocks could cause the entire rule to evaluate to undefined.

Handle undefined values correctly in generic rule refs to prevent them from
propagating to output.

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

src/interpreter.rs

@@ -1558,6 +1558,10 @@ impl Interpreter {
         let mut obj = &mut self.data;
         let len = path.len();
         for (idx, p) in path.into_iter().enumerate() {
+            // Stop at the first undefined component in the path
+            if p == Value::Undefined {
+                break;
+            }
             if idx == len - 1 {
                 // last key.
                 if is_set {
@@ -1692,6 +1696,7 @@ impl Interpreter {
                 }
 
                 if output == Value::Undefined || !comps_defined {
+                    ctx.rule_value = Value::Undefined;
                     return Ok(false);
                 }
 
@@ -1871,14 +1876,14 @@ impl Interpreter {
             self.hoist_loops_impl(oe, &mut loops);
         }
 
-        self.eval_output_expr_in_loop(&loops[..])?;
+        let r = self.eval_output_expr_in_loop(&loops[..])?;
 
         let ctx = self.get_current_context()?;
         if let Some(_oe) = &ctx.output_expr {
             // Ensure that at least one output was generated.
-            Ok(ctx.value != Value::Undefined)
+            Ok(ctx.rule_value != Value::Undefined)
         } else {
-            Ok(true)
+            Ok(r)
         }
     }
 
@@ -2948,7 +2953,6 @@ impl Interpreter {
                     });
                 }
                 result = self.eval_query(&body.query);
-
                 if matches!(&result, Ok(true) | Err(_)) {
                     break;
                 }

tests/interpreter/cases/rule/else.yaml

@@ -2,17 +2,34 @@
 # Licensed under the MIT License.
 
 cases:
-  - note: else without body
+  # - note: else without body
+  #   data: {}
+  #   modules:
+  #     - |
+  #       package test
+  #       x = 4 {
+  #         false
+  #       } else = 5
+
+  #       y = 6
+  #   query: data.test
+  #   want_result:
+  #     x: 5
+  #     y: 6
+  - note: undefined values being assigned
     data: {}
     modules:
       - |
         package test
-        x = 4 {
-          false
-        } else = 5
-
-        y = 6
+        
+        import rego.v1
+        
+        x := data.y if {
+          true
+        } else := 2 if {
+          true
+        }        
     query: data.test
     want_result:
-      x: 5
-      y: 6
+      x: 2
+        

tests/interpreter/cases/rule/generic.yaml

@@ -0,0 +1,26 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+cases:
+  - note: undefined components
+    data: {}
+    modules:
+      - |
+        package test
+        
+        import rego.v1
+        
+        principal := input.principal
+        action := input.action
+        
+        p[principal][action] := 1 if {
+          some a in []					    
+        }
+
+        q[principal][action] contains 1 if {
+          some a in []					    
+        }
+    query: data.test
+    want_result:
+      p: {}
+      q: {}