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tamer: asg::air::expr: Infer concrete/abstract state from child expressions 

See included documentation for more information.  This completes `MetaState`
inference, for now, until we are able to be notified when missing
identifiers acquire bindings.

DEV-13163
main
Mike Gerwitz 2023-08-04 13:13:43 -04:00
parent ad9b6d1582
commit 7001b50543
4 changed files with 201 additions and 28 deletions
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20
tamer/src/asg/air/expr.rs
View File

@ -92,12 +92,8 @@ impl ParseState for AirExprAggregate {
}
(BuildingExpr(es, poi), AirExpr(ExprStart(op, span))) => {
match poi.create_subexpr(ctx.asg_mut(), Expr::new(op, span)) {
Ok(oi) => {
Transition(BuildingExpr(es.push(poi), oi)).incomplete()
}
Err(e) => Transition(BuildingExpr(es, poi)).err(e),
}
let oi_child = ctx.asg_mut().create(Expr::new(op, span));
Transition(BuildingExpr(es.push(poi), oi_child)).incomplete()
}
(BuildingExpr(es, oi), AirExpr(ExprEnd(end))) => {
@ -107,13 +103,19 @@ impl ParseState for AirExprAggregate {
let oi_root = ctx.dangling_expr_oi();
match (es.pop(), dangling) {
((es, Some(poi)), _) => {
Transition(BuildingExpr(es, poi)).incomplete()
}
// This was a child expression
((es, Some(poi)), _) => poi
.add_completed_subexpr(ctx.asg_mut(), oi)
.map(|_| ())
.transition(BuildingExpr(es, poi)),
// Topmost expression, dangling.
((es, None), true) => {
Self::hold_dangling(ctx.asg_mut(), oi_root, oi)
.transition(Ready(es.done()))
}
// Topmost expression, reachable.
((es, None), false) => {
Transition(Ready(es.done())).incomplete()
}

81
tamer/src/asg/air/expr/test.rs
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@ -47,10 +47,15 @@ pub fn collect_subexprs(
asg: &Asg,
oi: ObjectIndex<Expr>,
) -> Vec<(ObjectIndex<Expr>, &Expr)> {
oi.edges(&asg)
let mut exprs = oi
.edges(&asg)
.filter_map(|rel| rel.narrow::<Expr>())
.map(|oi| (oi, oi.resolve(&asg)))
.collect::<Vec<_>>()
.collect::<Vec<_>>();
// Edge order is reversed.
exprs.reverse();
exprs
}
#[test]
@ -931,7 +936,7 @@ fn expr_referencing_missing_without_abstract_is_unknown() {
// but throw in a known reference to show that it doesn't override the
// missing one.
#[test]
fn expr_referencing_missing_with_concrete_without_abstract_is_unknown() {
fn expr_referencing_missing_with_concrete_without_abstract_is_maybe_concrete() {
#[rustfmt::skip]
let toks = [
ExprStart(ExprOp::Sum, S1),
@ -959,3 +964,73 @@ fn expr_referencing_missing_with_concrete_without_abstract_is_unknown() {
// so only one is missing.
assert_eq!(expr.meta_state(), MetaState::MaybeConcrete(1.unwrap_into()));
}
// If any child expression is not known to be concrete,
// then we cannot reasonably call the parent expression concrete either,
// because we must decend into the parent's tree in order to expand
// children.
#[test]
fn expr_is_maybe_concrete_if_any_child_is_maybe_concrete() {
#[rustfmt::skip]
let toks = [
ExprStart(ExprOp::Sum, S1), // A = 2 // ----------------.
BindIdent(spair("expr", S2)), // |
// |
// This should be MaybeConcrete because // |
// there is an inner missing reference. // |
ExprStart(ExprOp::Sum, S3), // B = 1 // ---------. <-: A1
ExprStart(ExprOp::Sum, S4), // C = 2 // --. <-' B1 |
// A couple children deep to make sure // | |
// this property is inherited by all // | |
// ancestors (B, A). // | |
RefIdent(spair("missing", S5)), // <-: C1 |
// | |
// A second missing reference. // | |
// Even though _this_ expression has two, // | |
// we want the parent B to see only a // | |
// single missing edge to C. // | |
RefIdent(spair("missing", S6)), // <-' C2 |
ExprEnd(S6), // |
ExprEnd(S7), // |
// |
// Concrete, // |
// to make sure our count isn't affected. // |
ExprStart(ExprOp::Sum, S8), // |
ExprEnd(S9), // |
// |
// A second abstract child for A. // |
ExprStart(ExprOp::Sum, S10), // D = 1 // --. <--------' A2
RefIdent(spair("missing", S11)), // <-' D1
ExprEnd(S12),
ExprEnd(S13),
];
let ctx = air_ctx_from_pkg_body_toks(toks);
let asg = ctx.asg_ref();
let oi_a = pkg_expect_ident_oi::<Expr>(&ctx, spair("expr", S20));
let a = oi_a.resolve(&asg);
let ae = collect_subexprs(asg, oi_a);
assert_eq!(ae.len(), 3); // abstract, concrete, abstract
let (oi_b, b) = ae[0];
let (_, d) = ae[2];
// Sanity check to make sure we have the exprs that we're expecting.
assert_eq!(S3.merge(S7).unwrap(), b.span());
assert_eq!(S10.merge(S12).unwrap(), d.span());
let be = collect_subexprs(asg, oi_b);
assert_eq!(be.len(), 1);
let (_, c) = be[0];
// We'll assert according to the visualization above,
// from inside out.
// Asserting individually helps to guide debugging with a narrow focus,
// and we want to fail on inner exprs first since effects compose
// outward.
assert_eq!(d.meta_state(), MetaState::MaybeConcrete(1.unwrap_into()));
assert_eq!(c.meta_state(), MetaState::MaybeConcrete(2.unwrap_into()));
assert_eq!(b.meta_state(), MetaState::MaybeConcrete(1.unwrap_into()));
assert_eq!(a.meta_state(), MetaState::MaybeConcrete(2.unwrap_into()));
}

1
tamer/src/asg/air/tpl/test.rs
View File

@ -161,7 +161,6 @@ fn tpl_within_expr() {
collect_subexprs(&asg, oi_expr)
.iter()
.map(|(_, expr)| expr.span())
.rev()
.collect::<Vec<_>>(),
);
}

127
tamer/src/asg/graph/object/expr.rs
View File

@ -26,6 +26,50 @@
//! so expressions both naturally compose and are able to be replaced with
//! the value that they represent without affecting the meaning of the
//! program.
//!
//! An expression is [_concrete_](`MetaState::Concrete`) if it requires no
//! expansion by the template system.
//! If an expression or any of its children reference any
//! [metavariables](super::Meta)
//! (template parameters),
//! then the expression will be [_abstract_](MetaState::Abstract).
//! Expressions' static bindings together with their referential
//! transparency means that a concrete expression is able to be moved and
//! copied to any other point in the program without changing its
//! meaning;
//! this includes the act of copying via template expansion.
//!
//! A _reference_ to another expression does not have any influence over
//! whether an expression is abstract or not.
//! In graph terms:
//! tree edges influence an expression's [`MetaState`],
//! but not cross edges.
//! Consider the following expression in XML notation to help with intuition
//! on this.
//! Assume that this is the body of some template with a single template
//! parameter identified as `@foo@`:
//!
//! ```xml
//! <!-- there are no metavariable references, so this is concrete -->
//! <c:sum id="conc">
//! <c:value-of name="#5" />
//! </c:sum>
//!
//! <!-- this is abstract because it requires expansion -->
//! <c:sum id="abstract">
//! <c:value-of name="@foo@" />
//! </c:sum>
//!
//! <!-- this is concrete... -->
//! <c:sum id="combine">
//! <c:value-of name="conc" />
//! <!-- ...even though `abstract` is abstract, because moving or
//! copying `combine` would have no effect on the meaning of the
//! the expression, and there is nothing to expand via the template
//! system -->
//! <c:value-of name="abstract" />
//! </c:sum>
//! ```
use super::{
ident::IdentDefinition, prelude::*, Doc, Ident, ObjectIndexToTree, Tpl,
@ -44,6 +88,8 @@ use super::ObjectKind;
/// The [`Span`] of an expression should be expanded to encompass not only
/// all child expressions,
/// but also any applicable closing span.
///
/// See the [parent module](self) for more information.
#[derive(Debug, PartialEq, Eq)]
pub struct Expr {
op: ExprOp,
@ -348,6 +394,20 @@ impl MetaState {
}
}
}
/// Determine how a child expression should impact whether this
/// expression is abstract.
fn observe_child(self, state: MetaState, span: Span) -> Self {
match state {
Self::Concrete => self,
Self::Abstract => self.found_abstract(),
// Since we track the number of missing edges to direct children,
// we treat the child subgraph as if it were a single node on
// the graph.
Self::MaybeConcrete(_) => self.found_missing(span),
}
}
}
impl Display for MetaState {
@ -384,10 +444,27 @@ object_rel! {
);
},
// Non-meta identifiers are just references.
// We don't care what they are as long as they're not
// metavariables.
Some(IdentDefinition::Expr(_) | IdentDefinition::Tpl(_)) => (),
// This is a _reference_ to another expression tree.
// Only tree edges influence our abstract status.
Some(IdentDefinition::Expr(_)) => (),
// Unlike the XSLT-based TAME,
// this reference can act as a template application,
// just as the `tree Tpl` edge below.
// TODO: We can expand closed expr templates here,
// since it's no different than referencing the inner
// expression.
Some(IdentDefinition::Tpl(_)) => diagnostic_todo!(
vec![
rel.to_oi.error("this references a template"),
rel.to_oi.help(
"only closed expression templates will be \
supported in this context"
)
],
"template references in an expression context are
not yet supported"
),
None => {
rel.from_oi.map_obj_inner(asg, |meta: MetaState| {
@ -404,10 +481,28 @@ object_rel! {
}
},
tree Expr,
tree Doc,
tree Expr {
fn pre_add_edge(
asg: &mut Asg,
rel: ProposedRel<Self, Self>,
commit: impl FnOnce(&mut Asg),
) -> Result<(), AsgError> {
let to = rel.to_oi.resolve(asg);
// Template application
let child_state = to.meta_state();
let span = to.span();
rel.from_oi.map_obj_inner(asg, |state: MetaState| {
state.observe_child(child_state, span)
});
Ok(commit(asg))
}
},
tree Doc,
// Deferred template application
tree Tpl,
}
}
@ -419,18 +514,20 @@ impl ObjectIndex<Expr> {
self.map_obj_inner(asg, |span: Span| span.merge(end).unwrap_or(span))
}
/// Create a new subexpression as the next child of this expression and
/// return the [`ObjectIndex`] of the new subexpression.
/// Add a completed subexpression as a child of a parent expression.
///
/// It is important that the subexpression has _completed parsing_ so
/// that edge hooks are able to conduct inference on the entirety of
/// the subexpression.
///
/// Sub-expressions maintain relative order to accommodate
/// non-associative and non-commutative expressions.
pub fn create_subexpr(
pub fn add_completed_subexpr(
self,
asg: &mut Asg,
expr: Expr,
oi_sub: ObjectIndex<Expr>,
) -> Result<ObjectIndex<Expr>, AsgError> {
let oi_subexpr = asg.create(expr);
oi_subexpr.add_tree_edge_from(asg, self)
self.add_tree_edge_to(asg, oi_sub)
}
/// Reference the value of the expression identified by `oi_ident` as if
@ -451,8 +548,8 @@ impl ObjectIndex<Expr> {
/// If this is not true,
/// consider using:
///
/// 1. [`Self::create_subexpr`] to create and assign ownership of
/// expressions contained within other expressions; or
/// 1. [`Self::add_completed_subexpr`] to create and assign ownership
/// of expressions contained within other expressions; or
/// 2. [`ObjectIndex<Ident>::bind_definition`] if this expression is to
/// be assigned to an identifier.
pub fn held_by(