Removes some panics (#529)

Co-authored-by: Craig Disselkoen <[email protected]>

cedar-policy-core/Cargo.toml

@@ -25,6 +25,7 @@ smol_str = { version = "0.2", features = ["serde"] }
 stacker = "0.1.15"
 arbitrary = { version = "1", features = ["derive"], optional = true }
 miette = { version = "5.9.0", features = ["serde"] }
+nonempty = "0.9.0"
 
 # decimal extension requires regex
 regex = { version = "1.8", features = ["unicode"], optional = true }

cedar-policy-core/src/ast/expr.rs

@@ -1510,7 +1510,7 @@ mod test {
         let e = Expr::has_attr(Expr::val("a"), "\0".into());
         assert_eq!(format!("{e}"), r#""a" has "\0""#);
         // `\`'s escaped form is `\\`
-        let e = Expr::has_attr(Expr::val("a"), r#"\"#.into());
+        let e = Expr::has_attr(Expr::val("a"), r"\".into());
         assert_eq!(format!("{e}"), r#""a" has "\\""#);
     }
 

cedar-policy-core/src/est.rs

@@ -221,21 +221,14 @@ impl Policy {
         id: Option<ast::PolicyID>,
     ) -> Result<ast::Template, FromJsonError> {
         let id = id.unwrap_or(ast::PolicyID::from_string("JSON policy"));
-        let conditions = match self.conditions.len() {
-            0 => ast::Expr::val(true),
-            _ => {
-                let mut conditions = self
-                    .conditions
-                    .into_iter()
-                    .map(|cond| cond.try_into_ast(id.clone()));
-                // PANIC SAFETY checked above that `conditions` has at least 1 element
-                #[allow(clippy::expect_used)]
-                let first = conditions
-                    .next()
-                    .expect("already checked there is at least 1")?;
-                ast::ExprBuilder::with_data(())
-                    .and_nary(first, conditions.collect::<Result<Vec<_>, _>>()?)
-            }
+        let mut conditions_iter = self
+            .conditions
+            .into_iter()
+            .map(|cond| cond.try_into_ast(id.clone()));
+        let conditions = match conditions_iter.next() {
+            None => ast::Expr::val(true),
+            Some(first) => ast::ExprBuilder::with_data(())
+                .and_nary(first?, conditions_iter.collect::<Result<Vec<_>, _>>()?),
         };
         Ok(ast::Template::new(
             id,