564 lines
20 KiB
Rust
564 lines
20 KiB
Rust
// Relationship between objects represented on ASG //
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// Copyright (C) 2014-2023 Ryan Specialty, LLC.
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//
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// This file is part of TAME.
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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//! Relationship betwen objects on the ASG.
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//!
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//! See (parent module)[super] for more information.
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use super::{
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Expr, Ident, Meta, Object, ObjectIndex, ObjectKind, OiPairObjectInner, Pkg,
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Root,
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};
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use crate::{
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asg::{graph::object::Tpl, Asg},
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f::Functor,
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span::Span,
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};
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use std::fmt::Display;
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pub use super::ObjectTy as ObjectRelTy;
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impl Display for ObjectRelTy {
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fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
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// At the time of writing,
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// this happens to be sufficient.
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std::fmt::Debug::fmt(self, f)
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}
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}
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/// Declare relations for an [`ObjectKind`].
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///
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/// This generates an [`ObjectRel`] type for the provided [`ObjectKind`] and
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/// binds it to the kind using [`ObjectRelatable`].
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///
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/// Each relationship must be explicitly specified as either a `tree` or
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/// `cross` edge.
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/// For more information on cross edges,
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/// see [`ObjectRel::is_cross_edge`].
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macro_rules! object_rel {
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(
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$(#[$attr:meta])+
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$from:ident -> {
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$($ety:ident $kind:ident,)*
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}
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) => {paste::paste! {
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/// Subset of [`ObjectKind`]s that are valid targets for edges from
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#[doc=concat!("[`", stringify!($from), "`].")]
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///
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$(#[$attr])+
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///
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/// See [`ObjectRel`] for more information.
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///
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/// [`ObjectKind`]: crate::asg::ObjectKind
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#[derive(Debug, PartialEq, Eq)]
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pub enum [<$from Rel>] {
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$($kind(ObjectIndex<$kind>),)*
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}
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impl ObjectRel<$from> for [<$from Rel>] {
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fn narrow<OB: ObjectRelFrom<$from> + ObjectRelatable>(
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self,
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) -> Option<ObjectIndex<OB>> {
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match self {
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$(Self::$kind(oi) => oi.filter_rel(),)*
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}
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}
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/// The root of the graph by definition has no cross edges.
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fn is_cross_edge<S, T>(
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&self,
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#[allow(unused_variables)] // used only for `dyn` edges
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rel: &$crate::asg::graph::object::rel::DynObjectRel<S, T>
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) -> bool {
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match self {
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$(
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Self::$kind(..) => object_rel!(@is_cross_edge $ety rel),
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)*
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#[allow(unreachable_patterns)] // for empty Rel types
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_ => unreachable!(
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concat!(stringify!($from), "Rel is empty")
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),
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}
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}
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}
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impl ObjectRelatable for $from {
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type Rel = [<$from Rel>];
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fn rel_ty() -> ObjectRelTy {
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ObjectRelTy::$from
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}
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fn new_rel_dyn(
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ty: ObjectRelTy,
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#[allow(unused_variables)] // for empty Rel
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oi: ObjectIndex<Object>,
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) -> Option<[<$from Rel>]> {
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match ty {
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$(
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ObjectRelTy::$kind => {
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Some(Self::Rel::$kind(oi.must_narrow_into()))
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},
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)*
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_ => None,
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}
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}
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}
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$(
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impl From<ObjectIndex<$kind>> for [<$from Rel>] {
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fn from(value: ObjectIndex<$kind>) -> Self {
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Self::$kind(value)
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}
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}
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)*
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}};
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// Static edge types.
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(@is_cross_edge cross $_:ident) => { true };
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(@is_cross_edge tree $_:ident) => { false };
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// Dynamic edge type.
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//
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// We consider an edge to be a cross edge iff it contains a context
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// span.
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// If it were _not_ a cross edge,
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// then the edge would represent ownership,
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// and the span information on the target would be sufficient context
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// on its own;
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// an edge only needs supplemental span information if there is
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// another context in which that object is referenced.
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(@is_cross_edge dyn $rel:ident) => { $rel.ctx_span().is_some() };
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}
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/// A dynamic relationship (edge) from one object to another before it has
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/// been narrowed.
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///
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/// The source and target of this edge are usually [`ObjectIndex`]es,
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/// but it is made generic (`S, T`) to support mapping while retaining
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/// useful metadata,
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/// e.g. to resolve an object while retaining the edge information.
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#[derive(Debug, PartialEq)]
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pub struct DynObjectRel<S = ObjectIndex<Object>, T = ObjectIndex<Object>>(
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(ObjectRelTy, ObjectRelTy),
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(S, T),
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Option<Span>,
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);
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impl<S, T> DynObjectRel<S, T> {
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pub(in super::super) fn new(
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from_ty: ObjectRelTy,
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to_ty: ObjectRelTy,
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src: S,
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target: T,
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ctx_span: Option<Span>,
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) -> Self {
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Self((from_ty, to_ty), (src, target), ctx_span)
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}
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/// The type of the source edge.
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pub fn source_ty(&self) -> ObjectRelTy {
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match self {
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Self((ty, _), ..) => *ty,
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}
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}
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/// The type of the target edge.
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pub fn target_ty(&self) -> ObjectRelTy {
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match self {
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Self((_, ty), ..) => *ty,
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}
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}
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/// The source of this relationship.
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pub fn source(&self) -> &S {
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match self {
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Self(_, (oi, _), _) => oi,
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}
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}
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/// The target of this relationship.
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///
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/// This type generally originates as [`ObjectIndex`] but can be mapped
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/// over to retain the structured edge data.
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pub fn target(&self) -> &T {
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match self {
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Self(_, (_, oi), _) => oi,
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}
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}
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/// A [`Span`] associated with the _relationship_ between the source and
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/// target objects,
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/// if any.
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pub fn ctx_span(&self) -> Option<Span> {
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match self {
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Self(_, _, ctx_span) => *ctx_span,
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}
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}
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}
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impl<S> DynObjectRel<S, ObjectIndex<Object>> {
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/// Attempt to narrow the target into the [`ObjectRel`] of `O`.
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///
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/// See [`ObjectRelatable::new_rel_dyn`] for more information.
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pub fn narrow_target<O: ObjectKind + ObjectRelatable>(
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&self,
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) -> Option<O::Rel> {
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O::new_rel_dyn(self.target_ty(), *self.target())
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}
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/// Pair the target [`ObjectIndex`] with its resolved [`Object`].
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///
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/// This allows the [`ObjectIndex`] to be refined alongside the inner
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/// [`ObjectKind`] so that callers can make use of the refined
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/// [`ObjectIndex`] without having to explicitly narrow themselves.
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/// While isn't any more or less safe than the manual alternative,
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/// it _does_ defend against logic bugs.
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pub fn resolve_target_oi_pair(
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self,
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asg: &Asg,
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) -> DynObjectRel<S, Object<OiPairObjectInner>> {
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self.map(|(soi, toi)| (soi, toi.resolve(asg).pair_oi(toi)))
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}
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/// Dynamically determine whether this edge represents a cross edge.
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///
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/// This function is intended for _dynamic_ edge types,
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/// which cannot be determined statically;
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/// it should be used only in situations where the potential edge types
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/// are unbounded,
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/// e.g. on an iterator yielding generalized [`ObjectIndex`]es during
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/// a full graph traversal.
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/// You should otherwise use [`ObjectRel::is_cross_edge`].
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///
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/// For more information on cross edges,
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/// see [`ObjectRel::is_cross_edge`].
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pub fn is_cross_edge(&self) -> bool {
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/// Generate cross-edge mappings between ObjectRelTy and the associated
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/// ObjectRel.
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///
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/// This is intended to both reduce boilerplate and to eliminate typos.
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///
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/// This mess will be optimized away,
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/// but exists so that cross edge definitions can exist alongside
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/// other relationship definitions for each individual object type,
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/// rather than having to maintain them in aggregate here.
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macro_rules! ty_cross_edge {
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($($ty:ident),*) => {
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match self.source_ty() {
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$(
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ObjectRelTy::$ty => {
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self.narrow_target::<$ty>().is_some_and(
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|rel| rel.is_cross_edge(self)
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)
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},
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)*
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}
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}
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}
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ty_cross_edge!(Root, Pkg, Ident, Expr, Tpl, Meta)
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}
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}
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impl<T> DynObjectRel<ObjectIndex<Object>, T> {
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/// Pair the source [`ObjectIndex`] with its resolved [`Object`].
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///
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/// This allows the [`ObjectIndex`] to be refined alongside the inner
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/// [`ObjectKind`] so that callers can make use of the refined
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/// [`ObjectIndex`] without having to explicitly narrow themselves.
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/// While isn't any more or less safe than the manual alternative,
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/// it _does_ defend against logic bugs.
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pub fn resolve_source_oi_pair(
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self,
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asg: &Asg,
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) -> DynObjectRel<Object<OiPairObjectInner>, T> {
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self.map(|(soi, toi)| (soi.resolve(asg).pair_oi(soi), toi))
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}
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}
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impl DynObjectRel<ObjectIndex<Object>, ObjectIndex<Object>> {
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/// Pair the source and target [`ObjectIndex`]es with their respective
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/// resolved [`Object`]s.
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///
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/// See [`Self::resolve_target_oi_pair`] and
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/// [`Self::resolve_source_oi_pair`] for more information.
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pub fn resolve_oi_pairs(
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self,
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asg: &Asg,
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) -> DynObjectRel<Object<OiPairObjectInner>, Object<OiPairObjectInner>>
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{
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self.resolve_source_oi_pair(asg).resolve_target_oi_pair(asg)
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}
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}
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impl<S, T, U, V> Functor<(S, T), (U, V)> for DynObjectRel<S, T> {
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type Target = DynObjectRel<U, V>;
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fn map(self, f: impl FnOnce((S, T)) -> (U, V)) -> Self::Target {
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match self {
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Self(tys, x, ctx_span) => DynObjectRel(tys, f(x), ctx_span),
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}
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}
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}
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impl<T: Display> Display for DynObjectRel<T> {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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let Self((from_ty, to_ty), (s, t), _) = self;
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write!(f, "dynamic edge {from_ty}->{to_ty} with {s}->{t}",)
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}
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}
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/// Indicate that an [`ObjectKind`] `Self` can be related to
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/// [`ObjectKind`] `OB` by creating an edge from `Self` to `OB`.
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///
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/// This trait defines a portion of the graph ontology,
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/// allowing [`Self`] to be related to `OB` by creating a directed edge
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/// from [`Self`] _to_ `OB`, as in:
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///
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/// ```text
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/// (Self) -> (OB)
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/// ```
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///
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/// While the data on the graph itself is dynamic and provided at runtime,
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/// the systems that _construct_ the graph using the runtime data can be
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/// statically analyzed by the type system to ensure that they only
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/// construct graphs that adhere to this schema.
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pub trait ObjectRelTo<OB: ObjectKind + ObjectRelatable> =
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ObjectRelatable where <Self as ObjectRelatable>::Rel: From<ObjectIndex<OB>>;
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/// Reverse of [`ObjectRelTo`].
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///
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/// This is primarily useful for avoiding `where` clauses,
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/// or for use in `impl Trait` specifications.
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pub trait ObjectRelFrom<OA: ObjectKind + ObjectRelatable> =
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ObjectRelatable where <OA as ObjectRelatable>::Rel: From<ObjectIndex<Self>>;
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/// Identify [`Self::Rel`] as a sum type consisting of the subset of
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/// [`Object`] variants representing the valid _target_ edges of
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/// [`Self`].
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///
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/// This is used to derive [`ObjectRelTo``],
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/// which can be used as a trait bound to assert a valid relationship
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/// between two [`Object`]s.
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pub trait ObjectRelatable: ObjectKind {
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/// Sum type representing a subset of [`Object`] variants that are valid
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/// targets for edges from [`Self`].
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///
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/// See [`ObjectRel`] for more information.
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type Rel: ObjectRel<Self>;
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/// The [`ObjectRelTy`] tag used to identify this [`ObjectKind`] as a
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/// target of a relation.
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fn rel_ty() -> ObjectRelTy;
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/// Represent a relation to another [`ObjectKind`] that cannot be
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/// statically known and must be handled at runtime.
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///
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/// A value of [`None`] means that the provided [`DynObjectRel`] is not
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/// valid for [`Self`].
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/// If the caller is utilizing edge data that is already present on the graph,
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/// then this means that the system is not properly upholding edge
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/// invariants
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/// (the graph's ontology)
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/// and the system ought to panic;
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/// this is a significant bug representing a problem with the
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/// correctness of the system.
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///
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/// See [`ObjectRel`] for more information.
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fn new_rel_dyn(
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ty: ObjectRelTy,
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oi: ObjectIndex<Object>,
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) -> Option<Self::Rel>;
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}
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impl<O: ObjectKind + ObjectRelatable> ObjectIndex<O> {
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pub fn rel_ty(&self) -> ObjectRelTy {
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O::rel_ty()
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}
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}
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/// A relationship to another [`ObjectKind`].
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///
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/// This trait is intended to be implemented by enums that represent the
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/// subset of [`ObjectKind`]s that are able to serve as edge targets for
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/// the [`ObjectRelatable`] that utilizes it as its
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/// [`ObjectRelatable::Rel`].
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///
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/// As described in the [module-level documentation](super),
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/// the concrete [`ObjectKind`] of an edge is generally not able to be
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/// determined statically outside of code paths that created the
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/// [`Object`] anew.
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/// But we _can_ at least narrow the types of [`ObjectKind`]s to those
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/// [`ObjectRelTo`]s that we know are valid,
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/// since the system is restricted (statically) to those edges when
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/// performing operations on the graph.
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///
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/// This [`ObjectRel`] represents that subset of [`ObjectKind`]s.
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/// A caller may decide to dispatch based on the type of edge it receives,
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/// or it may filter edges with [`Self::narrow`] in conjunction with
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/// [`Iterator::filter_map`]
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/// (for example).
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/// Since the wrapped value is an [`ObjectIndex`],
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/// the system will eventually panic if it attempts to reference a node
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/// that is not of the type expected by the edge,
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/// which can only happen if the edge has an incorrect [`ObjectRelTy`],
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/// meaning the graph is somehow corrupt
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/// (because system invariants were not upheld).
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///
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/// This affords us both runtime memory safety and static guarantees that
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/// the system is not able to generate an invalid graph that does not
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/// adhere to the prescribed ontology,
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/// provided that invariants are properly upheld by the
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/// [`asg`](crate::asg) module.
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pub trait ObjectRel<OA: ObjectKind + ObjectRelatable>: Sized {
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/// Attempt to narrow into the [`ObjectKind`] `OB`.
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///
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/// Unlike [`Object`] nodes,
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/// _this operation does not panic_,
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/// instead returning an [`Option`].
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/// If the relationship is of type `OB`,
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/// then [`Some`] will be returned with an inner
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/// [`ObjectIndex<OB>`](ObjectIndex).
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/// If the narrowing fails,
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/// [`None`] will be returned instead.
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///
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/// This return value is well-suited for [`Iterator::filter_map`] to
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/// query for edges of particular kinds.
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fn narrow<OB: ObjectRelFrom<OA> + ObjectRelatable>(
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self,
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) -> Option<ObjectIndex<OB>>;
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/// Attempt to narrow into the [`ObjectKind`] `OB`,
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/// but rather than returning the narrowed type,
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/// return `Option<Self>`.
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///
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/// This can be used with [`Iterator::filter_map`].
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/// By not being a [`bool`] predicate,
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/// we're able to provide a default trait implementation based on
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/// [`Self::narrow`] without requiring that [`Self`] implement
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/// [`Copy`].
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fn narrows_into<OB: ObjectRelFrom<OA> + ObjectRelatable>(
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self,
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) -> Option<Self>
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where
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Self: From<ObjectIndex<OB>>,
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{
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self.narrow::<OB>().map(Into::into)
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}
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/// Whether this relationship represents an ontological cross edge.
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///
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/// A _cross edge_ is an edge between two trees as described by the
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/// graph's ontology.
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/// Many objects on the graph represent trees,
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/// but contain references to other trees.
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/// Recognizing cross edges allows the system to understand when it is
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/// following an edge between two trees,
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/// which may require different behavior.
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///
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/// This contrasts to cross edges in the context of a graph traversal,
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/// where a tree is determined by a walk of the graph and may not take
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/// into consideration the meaning of edges.
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///
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/// _Because this is a property of the ontology rather than a structural
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/// interpretation of the graph,
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/// it must be manually verified by a human._
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/// An incorrect flagging of cross edges here will result in certain
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/// traversals being incorrect.
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///
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/// Implementation Context
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/// ======================
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/// It is important to understand why this method exists and how it may
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/// be used so that implementations of this trait do the right thing
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/// with regards to determining whether an edge ought to represent a
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/// cross edge.
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///
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/// For example,
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/// when generating a representation of an [`Expr`],
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/// a walk of the graph ought not consider an [`Ident`] reference to
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/// be part of the expression tree,
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/// otherwise the referenced expression would be inlined.
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/// Furthermore,
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/// visiting the referenced [`Ident`] ought not inhibit a later walk,
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/// since the walk must later traverse the [`Ident`] to reach the
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/// [`Object`] that it represents.
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/// Similarly,
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/// if the [`Ident`] has already been visited by a previous walk,
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/// we want to _re-visit_ it to output a reference as part of the
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/// referencing [`Expr`].
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///
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/// However,
|
||
/// this behavior is not always desirable.
|
||
/// In the case of a topological sort of the graph for linking,
|
||
/// cross edges ought to count as visitations since that dependency
|
||
/// must be calculated before the expression that needs it,
|
||
/// and we don't want to re-calculate it again later on.
|
||
///
|
||
/// The cross-edge is therefore an ontological fact,
|
||
/// but its _interpretation_ is context-dependent.
|
||
///
|
||
/// Note that the ontology is not intended to support back edges,
|
||
/// since they produce cycles,
|
||
/// except for exceptional situations
|
||
/// (e.g. function recursion which will hopefully be removed from
|
||
/// the language in the future).
|
||
/// With that said,
|
||
/// if an edge could conceivably be a back edge and not be rejected
|
||
/// from circular dependency checks,
|
||
/// then do _not_ assume that it is a cross edge without further
|
||
/// analysis,
|
||
/// which may require introducing more context to this method.
|
||
///
|
||
/// Dynamic Cross Edges
|
||
/// ==================
|
||
/// Sometimes a cross edge cannot be determined statically due to
|
||
/// ontological compromises.
|
||
/// For example,
|
||
/// a [`Tpl`]->[`Ident`] edge could be a reference to another tree,
|
||
/// as in the case of template application,
|
||
/// or the template could be serving as a container for that
|
||
/// definition.
|
||
/// The former case is a cross edge,
|
||
/// but the ladder is not.
|
||
///
|
||
/// We could introduce a layer of indirection on the graph to
|
||
/// disambiguate,
|
||
/// but that adds complexity to the graph that many different
|
||
/// subsystems need to concern themselves with.
|
||
/// But cross edge determination is fairly isolated,
|
||
/// needed only by traversals.
|
||
///
|
||
/// Therefore,
|
||
/// this method also receives a [`DynObjectRel`] reference,
|
||
/// which contains edge information.
|
||
/// The edge can be augmented with data that helps to determine,
|
||
/// at runtime,
|
||
/// whether that particular edge is a cross edge.
|
||
///
|
||
/// The use of [`DynObjectRel`] is heavy and effectively makes this
|
||
/// method useless for callers that do not deal directly with raw
|
||
/// [`Asg`] data;
|
||
/// it may be useful to refine this further in the future to correct
|
||
/// that,
|
||
/// once all use cases are clear.
|
||
fn is_cross_edge<S, T>(&self, rel: &DynObjectRel<S, T>) -> bool;
|
||
}
|