flowlog-build 0.3.0

Build-time FlowLog compiler for library mode.
Documentation 
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//! Rule structures for FlowLog Datalog programs.
//!
//! A rule is `head :- p1, p2, ..., pn.`
//! - Head: a single derived relation
//! - Body: predicates that must all be satisfied

use super::{Factor, Head, HeadArg, Predicate};
use crate::common::{FileId, Ignored, Span};
use crate::parser::error::{ParseError, grammar_bug};
use crate::parser::primitive::ConstType;
use crate::parser::{Lexeme, Rule, span_of};
use pest::iterators::Pair;
use std::fmt;

/// A complete FlowLog rule.
///
/// Declared `pub` (not `pub(crate)`) because it leaks through
/// `Catalog::from_rule` / `Program::rules` signatures that external
/// callers (flowlog-compiler, integration tests) consume. The rule's
/// inherent methods stay `pub(crate)` — external code only passes rules
/// by reference without inspecting fields.
#[derive(Clone, PartialEq, Eq, Hash)]
pub struct FlowLogRule {
    head: Head,
    rhs: Vec<Predicate>,
    span: Ignored<Span>,
}

impl fmt::Display for FlowLogRule {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "{} :- {}.",
            self.head,
            self.rhs
                .iter()
                .map(|p| p.to_string())
                .collect::<Vec<_>>()
                .join(", ")
        )
    }
}

impl fmt::Debug for FlowLogRule {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "{} :- {}.",
            self.head,
            self.rhs
                .iter()
                .map(|p| format!("{p:?}"))
                .collect::<Vec<_>>()
                .join(", ")
        )
    }
}

impl FlowLogRule {
    /// Construct a rule.
    #[must_use]
    pub(crate) fn new(head: Head, rhs: Vec<Predicate>) -> Self {
        Self {
            head,
            rhs,
            span: Ignored(Span::DUMMY),
        }
    }

    /// Source location this rule was parsed from.
    #[must_use]
    #[inline]
    pub(crate) fn span(&self) -> Span {
        self.span.0
    }

    /// Rule head.
    #[must_use]
    #[inline]
    pub(crate) fn head(&self) -> &Head {
        &self.head
    }

    /// Rule body (right-hand side predicates).
    #[must_use]
    #[inline]
    pub(crate) fn rhs(&self) -> &[Predicate] {
        &self.rhs
    }

    #[inline]
    pub(crate) fn head_mut(&mut self) -> &mut Head {
        &mut self.head
    }

    #[inline]
    pub(crate) fn rhs_mut(&mut self) -> &mut [Predicate] {
        &mut self.rhs
    }

    /// Extract constants from a fact's head.
    ///
    /// Panics if any head argument is not a simple constant.
    #[must_use]
    pub(crate) fn extract_constants_from_head(&self) -> Vec<ConstType> {
        let args = self.head.head_arguments();
        let mut out = Vec::with_capacity(args.len());
        for arg in args {
            let HeadArg::Arith(arith) = arg else {
                panic!("Fact head must contain only constants: {self}");
            };
            let Factor::Const(c) = arith.init() else {
                panic!("Fact head must contain only constants: {self}");
            };
            assert!(
                arith.is_const(),
                "Fact head must contain only constants: {self}"
            );
            out.push(c.clone());
        }
        out
    }

    /// Expand a multi-head / multi-body rule into one rule per
    /// (head, body) pair. Parenthesised `(A ; B)` disjunctions inside
    /// a conjunction distribute by cross-product.
    pub(crate) fn expand_from_parsed_rule(
        parsed_rule: Pair<Rule>,
        file: FileId,
    ) -> Result<Vec<Self>, ParseError> {
        let rule_span = span_of(&parsed_rule, file);
        let mut inner = parsed_rule.into_inner();

        let rule_heads_node = inner
            .next()
            .ok_or_else(|| grammar_bug("rule missing heads"))?;
        let mut heads: Vec<Head> = Vec::new();
        for h in rule_heads_node.into_inner() {
            heads.push(Head::from_parsed_rule(h, file)?);
        }

        let rule_bodies_node = inner
            .next()
            .ok_or_else(|| grammar_bug("rule missing bodies"))?;
        let bodies = expand_rule_bodies(rule_bodies_node, file)?;

        let mut out = Vec::with_capacity(heads.len() * bodies.len());
        for head in &heads {
            for body in &bodies {
                out.push(Self {
                    head: head.clone(),
                    rhs: body.clone(),
                    span: Ignored(rule_span),
                });
            }
        }
        Ok(out)
    }
}

fn expand_rule_bodies(node: Pair<Rule>, file: FileId) -> Result<Vec<Vec<Predicate>>, ParseError> {
    let mut alternatives = Vec::new();
    for predicates_node in node.into_inner() {
        alternatives.extend(expand_predicates(predicates_node, file)?);
    }
    Ok(alternatives)
}

/// Expand one comma-separated `predicates` node, distributing any
/// nested `(A ; B)` groups by cross-product.
fn expand_predicates(node: Pair<Rule>, file: FileId) -> Result<Vec<Vec<Predicate>>, ParseError> {
    let mut acc: Vec<Vec<Predicate>> = vec![Vec::new()];
    for pred_node in node.into_inner() {
        let inner = pred_node
            .into_inner()
            .next()
            .ok_or_else(|| grammar_bug("predicate missing inner"))?;
        if matches!(inner.as_rule(), Rule::disjunction_group) {
            let bodies_node = inner
                .into_inner()
                .next()
                .ok_or_else(|| grammar_bug("disjunction_group missing inner rule_bodies"))?;
            let nested = expand_rule_bodies(bodies_node, file)?;
            let mut next = Vec::with_capacity(acc.len() * nested.len());
            for prefix in &acc {
                for alt in &nested {
                    let mut combined = prefix.clone();
                    combined.extend(alt.iter().cloned());
                    next.push(combined);
                }
            }
            acc = next;
        } else {
            let p = Predicate::from_inner(inner, file)?;
            for conjunction in &mut acc {
                conjunction.push(p.clone());
            }
        }
    }
    Ok(acc)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::parser::AggregationOperator;
    use crate::parser::logic::{Aggregation, Arithmetic, Factor};
    use crate::parser::primitive::ConstType;

    fn head_const(v: ConstType) -> HeadArg {
        HeadArg::Arith(Arithmetic::new(Factor::Const(v), vec![]))
    }
    fn head_named(name: &str, args: Vec<HeadArg>) -> Head {
        Head::new(name.into(), args)
    }

    #[test]
    fn extract_constants() {
        let head = head_named(
            "facts",
            vec![
                head_const(ConstType::Int(42)),
                head_const(ConstType::Text("hello".into())),
            ],
        );
        let r = FlowLogRule::new(head, vec![]);
        let c = r.extract_constants_from_head();
        assert_eq!(c, vec![ConstType::Int(42), ConstType::Text("hello".into())]);
    }

    #[test]
    #[should_panic(expected = "Fact head must contain only constants")]
    fn extract_constants_panics_on_var() {
        let head = head_named(
            "invalid",
            vec![head_const(ConstType::Int(1)), HeadArg::Var("X".into())],
        );
        let _ = FlowLogRule::new(head, vec![]).extract_constants_from_head();
    }

    #[test]
    #[should_panic(expected = "Fact head must contain only constants")]
    fn extract_constants_panics_on_aggregation() {
        let agg = Aggregation::new(
            AggregationOperator::Sum,
            Arithmetic::new(Factor::Var("X".into()), vec![]),
        );
        let head = head_named(
            "invalid",
            vec![head_const(ConstType::Int(1)), HeadArg::Aggregation(agg)],
        );
        let _ = FlowLogRule::new(head, vec![]).extract_constants_from_head();
    }
}