cedar_policy_validator/cedar_schema/
fmt.rs

/*
 * Copyright Cedar Contributors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

//! `Display` implementations for formatting a [`json_schema::Fragment`] in the
//! Cedar schema syntax

use std::{collections::HashSet, fmt::Display};

use itertools::Itertools;
use miette::Diagnostic;
use nonempty::NonEmpty;
use smol_str::{SmolStr, ToSmolStr};
use thiserror::Error;

use crate::{json_schema, RawName};

impl<N: Display> Display for json_schema::Fragment<N> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        for (ns, def) in &self.0 {
            match ns {
                None => write!(f, "{def}")?,
                Some(ns) => write!(f, "namespace {ns} {{\n{def}}}\n")?,
            }
        }
        Ok(())
    }
}

impl<N: Display> Display for json_schema::NamespaceDefinition<N> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        for (n, ty) in &self.common_types {
            writeln!(f, "type {n} = {ty};")?
        }
        for (n, ty) in &self.entity_types {
            writeln!(f, "entity {n}{ty};")?
        }
        for (n, a) in &self.actions {
            writeln!(f, "action \"{}\"{a};", n.escape_debug())?
        }
        Ok(())
    }
}

impl<N: Display> Display for json_schema::Type<N> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            json_schema::Type::Type(ty) => match ty {
                json_schema::TypeVariant::Boolean => write!(f, "__cedar::Bool"),
                json_schema::TypeVariant::Entity { name } => write!(f, "{name}"),
                json_schema::TypeVariant::EntityOrCommon { type_name } => {
                    write!(f, "{type_name}")
                }
                json_schema::TypeVariant::Extension { name } => write!(f, "__cedar::{name}"),
                json_schema::TypeVariant::Long => write!(f, "__cedar::Long"),
                json_schema::TypeVariant::Record(rty) => write!(f, "{rty}"),
                json_schema::TypeVariant::Set { element } => write!(f, "Set < {element} >"),
                json_schema::TypeVariant::String => write!(f, "__cedar::String"),
            },
            json_schema::Type::CommonTypeRef { type_name } => write!(f, "{type_name}"),
        }
    }
}

impl<N: Display> Display for json_schema::RecordType<N> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{{")?;
        for (i, (n, ty)) in self.attributes.iter().enumerate() {
            write!(
                f,
                "\"{}\"{}: {}",
                n.escape_debug(),
                if ty.required { "" } else { "?" },
                ty.ty
            )?;
            if i < (self.attributes.len() - 1) {
                write!(f, ", ")?;
            }
        }
        write!(f, "}}")?;
        Ok(())
    }
}

/// Create a non-empty with borrowed contents from a slice
fn non_empty_slice<T>(v: &[T]) -> Option<NonEmpty<&T>> {
    let vs: Vec<&T> = v.iter().collect();
    NonEmpty::from_vec(vs)
}

fn fmt_vec<T: Display>(f: &mut std::fmt::Formatter<'_>, ets: NonEmpty<T>) -> std::fmt::Result {
    let contents = ets.iter().map(T::to_string).join(", ");
    write!(f, "[{contents}]")
}

impl<N: Display> Display for json_schema::EntityType<N> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        if let Some(non_empty) = non_empty_slice(&self.member_of_types) {
            write!(f, " in ")?;
            fmt_vec(f, non_empty)?;
        }

        let ty = &self.shape;
        // Don't print `= { }`
        if !ty.is_empty_record() {
            write!(f, " = {ty}")?;
        }

        if let Some(tags) = &self.tags {
            write!(f, " tags {tags}")?;
        }

        Ok(())
    }
}

impl<N: Display> Display for json_schema::ActionType<N> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        if let Some(parents) = self
            .member_of
            .as_ref()
            .and_then(|refs| non_empty_slice(refs.as_slice()))
        {
            write!(f, " in ")?;
            fmt_vec(f, parents)?;
        }
        if let Some(spec) = &self.applies_to {
            match (
                non_empty_slice(spec.principal_types.as_slice()),
                non_empty_slice(spec.resource_types.as_slice()),
            ) {
                // One of the lists is empty
                // This can only be represented by the empty action
                // This implies an action group
                (None, _) | (_, None) => {
                    write!(f, "")?;
                }
                // Both list are non empty
                (Some(ps), Some(rs)) => {
                    write!(f, " appliesTo {{")?;
                    write!(f, "\n  principal: ")?;
                    fmt_vec(f, ps)?;
                    write!(f, ",\n  resource: ")?;
                    fmt_vec(f, rs)?;
                    write!(f, ",\n  context: {}", &spec.context.0)?;
                    write!(f, "\n}}")?;
                }
            }
        }
        // No `appliesTo` key: action does not apply to anything
        Ok(())
    }
}

/// Error converting a schema to the Cedar syntax
#[derive(Debug, Diagnostic, Error)]
pub enum ToCedarSchemaSyntaxError {
    /// Collisions between names prevented the conversion to the Cedar syntax
    #[diagnostic(transparent)]
    #[error(transparent)]
    NameCollisions(#[from] NameCollisionsError),
}

/// Duplicate names were found in the schema
#[derive(Debug, Error, Diagnostic)]
#[error("There are name collisions: [{}]", .names.iter().join(", "))]
pub struct NameCollisionsError {
    /// Names that had collisions
    names: NonEmpty<SmolStr>,
}

impl NameCollisionsError {
    /// Get the names that had collisions
    pub fn names(&self) -> impl Iterator<Item = &str> {
        self.names.iter().map(smol_str::SmolStr::as_str)
    }
}

/// Convert a [`json_schema::Fragment`] to a string containing the Cedar schema syntax
///
/// As of this writing, this existing code throws an error if any
/// fully-qualified name in a non-empty namespace is a valid common type and
/// also a valid entity type.
//
// Two notes:
// 1) This check is more conservative than necessary. Schemas are allowed to
// shadow an entity type with a common type declaration in the same namespace;
// see RFCs 24 and 70. What the Cedar syntax can't express is if, in that
// situation, we then specifically refer to the shadowed entity type name.  But
// it's harder to walk all type references than it is to walk all type
// declarations, so the conservative code here is fine; we can always make it
// less conservative in the future without breaking people.
// 2) This code is also likely the cause of #1063; see that issue
pub fn json_schema_to_cedar_schema_str<N: Display>(
    json_schema: &json_schema::Fragment<N>,
) -> Result<String, ToCedarSchemaSyntaxError> {
    let mut name_collisions: Vec<SmolStr> = Vec::new();
    for (name, ns) in json_schema.0.iter().filter(|(name, _)| !name.is_none()) {
        let entity_types: HashSet<SmolStr> = ns
            .entity_types
            .keys()
            .map(|ty_name| {
                RawName::new_from_unreserved(ty_name.clone())
                    .qualify_with_name(name.as_ref())
                    .to_smolstr()
            })
            .collect();
        let common_types: HashSet<SmolStr> = ns
            .common_types
            .keys()
            .map(|ty_name| {
                RawName::new_from_unreserved(ty_name.clone().into())
                    .qualify_with_name(name.as_ref())
                    .to_smolstr()
            })
            .collect();
        name_collisions.extend(entity_types.intersection(&common_types).cloned());
    }
    if let Some(non_empty_collisions) = NonEmpty::from_vec(name_collisions) {
        return Err(NameCollisionsError {
            names: non_empty_collisions,
        }
        .into());
    }
    Ok(json_schema.to_string())
}

#[cfg(test)]
mod tests {
    use cedar_policy_core::extensions::Extensions;

    use crate::cedar_schema::parser::parse_cedar_schema_fragment;

    #[test]
    fn rfc_example() {
        let src = "entity User = {
            jobLevel: Long,
          } tags Set<String>;
          entity Document = {
            owner: User,
          } tags Set<String>;";
        let (cedar_schema, _) =
            parse_cedar_schema_fragment(src, Extensions::none()).expect("should parse");
        let printed_cedar_schema = cedar_schema.to_cedarschema().expect("should convert");
        let (parsed_cedar_schema, _) =
            parse_cedar_schema_fragment(&printed_cedar_schema, Extensions::none())
                .expect("should parse");
        assert_eq!(cedar_schema, parsed_cedar_schema);
    }
}
cedar_policy_validator/cedar_schema/fmt.rs

cedar_policy_validator/cedar_schema/
fmt.rs
