disambiguate empty sets from empty maps

according to the grammar, `{}` could either mean *empty set* or *empty map*. Due to how the parser was written, it was always an empty set, and there was no way to have an empty map literal.

This is an issue because empty maps would still be displayed as `{}`, and maps have a different api than sets, resulting in evaluation errors.

This commit introduces `{,}` as the empty set literal, while `{}` is the empty map. The goal here is to be consistent with JSON, the reason why we chose the current syntax for arrays and maps.

biscuit-auth/examples/testcases.rs

@@ -1378,6 +1378,9 @@ fn expressions(target: &str, root: &KeyPair, test: bool) -> TestResult {
         check if {1, 2, 3}.intersection({1, 2}).contains(1);
         // chained method calls with unary method
         check if {1, 2, 3}.intersection({1, 2}).length() === 2;
+
+        // empty set literal
+        check if {,}.length() === 0;
     "#)
         .build_with_rng(&root, SymbolTable::default(), &mut rng)
         .unwrap();

biscuit-auth/samples/README.md

@@ -1321,6 +1321,7 @@ check if {1, 2}.intersection({2, 3}) === {2};
 check if {1, 2}.union({2, 3}) === {1, 2, 3};
 check if {1, 2, 3}.intersection({1, 2}).contains(1);
 check if {1, 2, 3}.intersection({1, 2}).length() === 2;
+check if {,}.length() === 0;
 ```
 
 ### validation
@@ -1331,7 +1332,7 @@ allow if true;
 ```
 
 revocation ids:
-- `d0420227266e3583a42dfaa0e38550d99f681d150dd18856f3af9a697bc9c5c8bf06b4b0fe5b9df0377d1b963574e2fd210a0a76a8b0756a65f640c602bebd07`
+- `fa358e4e3bea896415b1859e6cd347e64e1918fb86e31ae3fe208628321576a47f7a269760357e291c827ec9cbe322074f6860a546207a64e133c83a214bb505`
 
 authorizer world:
 ```
@@ -1372,6 +1373,7 @@ World {
             "check if true",
             "check if true === true",
             "check if {\"abc\", \"def\"}.contains(\"abc\")",
+            "check if {,}.length() === 0",
             "check if {1, 2, 3}.intersection({1, 2}).contains(1)",
             "check if {1, 2, 3}.intersection({1, 2}).length() === 2",
             "check if {1, 2} === {1, 2}",

biscuit-auth/samples/samples.json

@@ -1276,7 +1276,7 @@
           ],
           "public_keys": [],
           "external_key": null,
-          "code": "check if true;\ncheck if !false;\ncheck if true === true;\ncheck if false === false;\ncheck if 1 < 2;\ncheck if 2 > 1;\ncheck if 1 <= 2;\ncheck if 1 <= 1;\ncheck if 2 >= 1;\ncheck if 2 >= 2;\ncheck if 3 === 3;\ncheck if 1 + 2 * 3 - 4 / 2 === 5;\ncheck if \"hello world\".starts_with(\"hello\"), \"hello world\".ends_with(\"world\");\ncheck if \"aaabde\".matches(\"a*c?.e\");\ncheck if \"aaabde\".contains(\"abd\");\ncheck if \"aaabde\" === \"aaa\" + \"b\" + \"de\";\ncheck if \"abcD12\" === \"abcD12\";\ncheck if \"abcD12\".length() === 6;\ncheck if \"é\".length() === 2;\ncheck if 2019-12-04T09:46:41Z < 2020-12-04T09:46:41Z;\ncheck if 2020-12-04T09:46:41Z > 2019-12-04T09:46:41Z;\ncheck if 2019-12-04T09:46:41Z <= 2020-12-04T09:46:41Z;\ncheck if 2020-12-04T09:46:41Z >= 2020-12-04T09:46:41Z;\ncheck if 2020-12-04T09:46:41Z >= 2019-12-04T09:46:41Z;\ncheck if 2020-12-04T09:46:41Z >= 2020-12-04T09:46:41Z;\ncheck if 2020-12-04T09:46:41Z === 2020-12-04T09:46:41Z;\ncheck if hex:12ab === hex:12ab;\ncheck if {1, 2}.contains(2);\ncheck if {2019-12-04T09:46:41Z, 2020-12-04T09:46:41Z}.contains(2020-12-04T09:46:41Z);\ncheck if {false, true}.contains(true);\ncheck if {\"abc\", \"def\"}.contains(\"abc\");\ncheck if {hex:12ab, hex:34de}.contains(hex:34de);\ncheck if {1, 2}.contains({2});\ncheck if {1, 2} === {1, 2};\ncheck if {1, 2}.intersection({2, 3}) === {2};\ncheck if {1, 2}.union({2, 3}) === {1, 2, 3};\ncheck if {1, 2, 3}.intersection({1, 2}).contains(1);\ncheck if {1, 2, 3}.intersection({1, 2}).length() === 2;\n",
+          "code": "check if true;\ncheck if !false;\ncheck if true === true;\ncheck if false === false;\ncheck if 1 < 2;\ncheck if 2 > 1;\ncheck if 1 <= 2;\ncheck if 1 <= 1;\ncheck if 2 >= 1;\ncheck if 2 >= 2;\ncheck if 3 === 3;\ncheck if 1 + 2 * 3 - 4 / 2 === 5;\ncheck if \"hello world\".starts_with(\"hello\"), \"hello world\".ends_with(\"world\");\ncheck if \"aaabde\".matches(\"a*c?.e\");\ncheck if \"aaabde\".contains(\"abd\");\ncheck if \"aaabde\" === \"aaa\" + \"b\" + \"de\";\ncheck if \"abcD12\" === \"abcD12\";\ncheck if \"abcD12\".length() === 6;\ncheck if \"é\".length() === 2;\ncheck if 2019-12-04T09:46:41Z < 2020-12-04T09:46:41Z;\ncheck if 2020-12-04T09:46:41Z > 2019-12-04T09:46:41Z;\ncheck if 2019-12-04T09:46:41Z <= 2020-12-04T09:46:41Z;\ncheck if 2020-12-04T09:46:41Z >= 2020-12-04T09:46:41Z;\ncheck if 2020-12-04T09:46:41Z >= 2019-12-04T09:46:41Z;\ncheck if 2020-12-04T09:46:41Z >= 2020-12-04T09:46:41Z;\ncheck if 2020-12-04T09:46:41Z === 2020-12-04T09:46:41Z;\ncheck if hex:12ab === hex:12ab;\ncheck if {1, 2}.contains(2);\ncheck if {2019-12-04T09:46:41Z, 2020-12-04T09:46:41Z}.contains(2020-12-04T09:46:41Z);\ncheck if {false, true}.contains(true);\ncheck if {\"abc\", \"def\"}.contains(\"abc\");\ncheck if {hex:12ab, hex:34de}.contains(hex:34de);\ncheck if {1, 2}.contains({2});\ncheck if {1, 2} === {1, 2};\ncheck if {1, 2}.intersection({2, 3}) === {2};\ncheck if {1, 2}.union({2, 3}) === {1, 2, 3};\ncheck if {1, 2, 3}.intersection({1, 2}).contains(1);\ncheck if {1, 2, 3}.intersection({1, 2}).length() === 2;\ncheck if {,}.length() === 0;\n",
           "version": 3
         }
       ],
@@ -1317,6 +1317,7 @@
                   "check if true",
                   "check if true === true",
                   "check if {\"abc\", \"def\"}.contains(\"abc\")",
+                  "check if {,}.length() === 0",
                   "check if {1, 2, 3}.intersection({1, 2}).contains(1)",
                   "check if {1, 2, 3}.intersection({1, 2}).length() === 2",
                   "check if {1, 2} === {1, 2}",
@@ -1339,7 +1340,7 @@
           },
           "authorizer_code": "allow if true;\n",
           "revocation_ids": [
-            "d0420227266e3583a42dfaa0e38550d99f681d150dd18856f3af9a697bc9c5c8bf06b4b0fe5b9df0377d1b963574e2fd210a0a76a8b0756a65f640c602bebd07"
+            "fa358e4e3bea896415b1859e6cd347e64e1918fb86e31ae3fe208628321576a47f7a269760357e291c827ec9cbe322074f6860a546207a64e133c83a214bb505"
           ]
         }
       }

biscuit-auth/src/datalog/symbol.rs

@@ -198,11 +198,15 @@ impl SymbolTable {
                 }
             }
             Term::Set(s) => {
-                let terms = s
-                    .iter()
-                    .map(|term| self.print_term(term))
-                    .collect::<Vec<_>>();
-                format!("{{{}}}", terms.join(", "))
+                if s.is_empty() {
+                    "{,}".to_string()
+                } else {
+                    let terms = s
+                        .iter()
+                        .map(|term| self.print_term(term))
+                        .collect::<Vec<_>>();
+                    format!("{{{}}}", terms.join(", "))
+                }
             }
             Term::Null => "null".to_string(),
             Term::Array(a) => {

biscuit-auth/src/token/builder.rs

@@ -333,4 +333,8 @@ check if true trusting ed25519/6e9e6d5a75cf0c0e87ec1256b4dfed0ca3ba452912d213fcc
             })
         );
     }
+    #[test]
+    fn empty_set_display() {
+        assert_eq!(Term::Set(BTreeSet::new()).to_string(), "{,}");
+    }
 }

biscuit-auth/src/token/builder/term.rs

@@ -359,8 +359,12 @@ impl fmt::Display for Term {
                 }
             }
             Term::Set(s) => {
-                let terms = s.iter().map(|term| term.to_string()).collect::<Vec<_>>();
-                write!(f, "{{{}}}", terms.join(", "))
+                if s.is_empty() {
+                    write!(f, "{{,}}")
+                } else {
+                    let terms = s.iter().map(|term| term.to_string()).collect::<Vec<_>>();
+                    write!(f, "{{{}}}", terms.join(", "))
+                }
             }
             Term::Parameter(s) => {
                 write!(f, "{{{}}}", s)

biscuit-parser/src/parser.rs

@@ -864,8 +864,16 @@ fn null(i: &str) -> IResult<&str, builder::Term, Error> {
 }
 
 fn set(i: &str) -> IResult<&str, builder::Term, Error> {
+    alt((empty_set, non_empty_set))(i)
+}
+
+fn empty_set(i: &str) -> IResult<&str, builder::Term, Error> {
+    tag("{,}")(i).map(|(i, _)| (i, builder::set(BTreeSet::new())))
+}
+
+fn non_empty_set(i: &str) -> IResult<&str, builder::Term, Error> {
     let (i, _) = preceded(space0, char('{'))(i)?;
-    let (i, mut list) = cut(separated_list0(preceded(space0, char(',')), term_in_set))(i)?;
+    let (i, mut list) = cut(separated_list1(preceded(space0, char(',')), term_in_set))(i)?;
 
     let mut set = BTreeSet::new();
 
@@ -960,7 +968,7 @@ fn term(i: &str) -> IResult<&str, builder::Term, Error> {
     preceded(
         space0,
         alt((
-            parameter, string, date, variable, integer, bytes, boolean, null, set, array, parse_map,
+            parameter, string, date, variable, integer, bytes, boolean, null, array, parse_map, set,
         )),
     )(i)
 }
@@ -2659,4 +2667,18 @@ mod tests {
             ))
         );
     }
+
+    #[test]
+    fn empty_set_map() {
+        use builder::{map, set};
+
+        assert_eq!(
+            super::expr("{,}").map(|(i, o)| (i, o.opcodes())),
+            Ok(("", vec![Op::Value(set(Default::default()))],))
+        );
+        assert_eq!(
+            super::expr("{}").map(|(i, o)| (i, o.opcodes())),
+            Ok(("", vec![Op::Value(map(Default::default()))],))
+        );
+    }
 }