Support SELF keyword in Podlang parser (#368)

* Support SELF keyword in Podlang parser

* Add pretty-printing for SELF

src/lang/grammar.pest

@@ -68,7 +68,8 @@ literal_value = {
     literal_raw |
     literal_pod_id |
     literal_string |
-    literal_int
+    literal_int |
+    self_keyword
 }
 
 // Primitive literal types

src/lang/mod.rs

@@ -34,7 +34,7 @@ mod tests {
         middleware::{
             hash_str, CustomPredicate, CustomPredicateBatch, CustomPredicateRef, Key,
             NativePredicate, Params, PodId, PodType, Predicate, RawValue, StatementTmpl,
-            StatementTmplArg, Value, Wildcard, KEY_SIGNER, KEY_TYPE,
+            StatementTmplArg, Value, Wildcard, KEY_SIGNER, KEY_TYPE, SELF,
         },
     };
 
@@ -877,6 +877,7 @@ mod tests {
                 Equal(?E["int"], {})
                 Equal(?F["bool"], {})
                 Equal(?G["sk"], {})
+                Equal(?H["self"], SELF)
             )
         "#,
             Value::from(pk).to_podlang_string(),
@@ -895,6 +896,8 @@ mod tests {
                 Equal(?D["string"], "hello")
                 Equal(?E["int"], 123)
                 Equal(?F["bool"], true)
+                Equal(?G["sk"], SecretKey(random_secret_key_base_64))
+                Equal(?H["self"], SELF)
             )
         */
 
@@ -902,8 +905,6 @@ mod tests {
         let processed = parse(&input, &params, &[])?;
         let request_templates = processed.request_templates;
 
-        assert_eq!(request_templates.len(), 7);
-
         let expected_templates = vec![
             StatementTmpl {
                 pred: Predicate::Native(NativePredicate::Equal),
@@ -933,6 +934,10 @@ mod tests {
                 pred: Predicate::Native(NativePredicate::Equal),
                 args: vec![sta_ak(("G", 6), "sk"), sta_lit(Value::from(sk))],
             },
+            StatementTmpl {
+                pred: Predicate::Native(NativePredicate::Equal),
+                args: vec![sta_ak(("H", 7), "self"), sta_lit(Value::from(SELF))],
+            },
         ];
 
         assert_eq!(request_templates, expected_templates);

src/lang/pretty_print.rs

@@ -507,6 +507,16 @@ mod tests {
         assert_round_trip(&input);
     }
 
+    #[test]
+    fn test_round_trip_self() {
+        let input = r#"
+            self_test(Pod) = AND(
+                Equal(?Pod["self"], SELF)
+            )
+        "#;
+        assert_round_trip(input);
+    }
+
     #[test]
     fn test_pretty_print_demonstration() {
         let input = r#"

src/lang/processor.rs

@@ -817,6 +817,7 @@ fn process_literal_value(
             })?;
             Ok(Value::from(secret_key))
         }
+        Rule::self_keyword => Ok(Value::from(middleware::SELF)),
         _ => unreachable!("Unexpected rule: {:?}", inner_lit.as_rule()),
     }
 }