chore(middleware): additional error reporting for custom predicates

src/frontend/error.rs

@@ -22,8 +22,13 @@ fn display_wc_map(wc_map: &[Option<Value>]) -> String {
 pub enum InnerError {
     #[error("{0} {1} is over the limit {2}")]
     MaxLength(String, usize, usize),
-    #[error("{0} doesn't match {1:#}.\nWildcard map:\n{map}", map=display_wc_map(.2))]
-    StatementsDontMatch(Statement, StatementTmpl, Vec<Option<Value>>),
+    #[error("{0} doesn't match {1:#}.\nWildcard map:\n{map}\nInternal error: {3}", map=display_wc_map(.2))]
+    StatementsDontMatch(
+        Statement,
+        StatementTmpl,
+        Vec<Option<Value>>,
+        crate::middleware::Error,
+    ),
     #[error("invalid arguments to {0} operation")]
     OpInvalidArgs(String),
     // Other
@@ -76,8 +81,9 @@ impl Error {
         s0: Statement,
         s1: StatementTmpl,
         wc_map: Vec<Option<Value>>,
+        mid_error: crate::middleware::Error,
     ) -> Self {
-        new!(StatementsDontMatch(s0, s1, wc_map))
+        new!(StatementsDontMatch(s0, s1, wc_map, mid_error))
     }
     pub(crate) fn max_length(obj: String, found: usize, expect: usize) -> Self {
         new!(MaxLength(obj, found, expect))

src/frontend/mod.rs

@@ -472,11 +472,14 @@ impl MainPodBuilder {
                 for (st_tmpl, st) in pred.statements.iter().zip(args.iter()) {
                     let st_args = st.args();
                     for (st_tmpl_arg, st_arg) in st_tmpl.args.iter().zip(&st_args) {
-                        if !check_st_tmpl(st_tmpl_arg, st_arg, &mut wildcard_map) {
+                        if let Err(st_tmpl_check_error) =
+                            check_st_tmpl(st_tmpl_arg, st_arg, &mut wildcard_map)
+                        {
                             return Err(Error::statements_dont_match(
                                 st.clone(),
                                 st_tmpl.clone(),
                                 wildcard_map,
+                                st_tmpl_check_error,
                             ));
                         }
                     }

src/middleware/error.rs

@@ -2,7 +2,10 @@
 
 use std::{backtrace::Backtrace, fmt::Debug};
 
-use crate::middleware::{Operation, Statement, StatementArg};
+use crate::middleware::{
+    CustomPredicate, Key, Operation, PodId, Statement, StatementArg, StatementTmplArg, Value,
+    Wildcard,
+};
 
 pub type Result<T, E = Error> = core::result::Result<T, E>;
 
@@ -18,6 +21,22 @@ pub enum MiddlewareInnerError {
     MaxLength(String, usize, usize),
     #[error("{0} amount of {1} should be {1} but it's {2}")]
     DiffAmount(String, String, usize, usize),
+    #[error("{0} should be assigned the value {1} but has previously been assigned {2}")]
+    InvalidWildcardAssignment(Wildcard, Value, Value),
+    #[error("{0} matches POD ID {1}, yet the template key {2} does not match {3}")]
+    MismatchedAnchoredKeyInStatementTmplArg(Wildcard, PodId, Key, Key),
+    #[error("{0} does not match against {1}")]
+    MismatchedStatementTmplArg(StatementTmplArg, StatementArg),
+    #[error("Value {0} does not match argument {1} with index {2} in the following custom predicate:\n{3}")]
+    MismatchedWildcardValueAndStatementArg(Value, Value, usize, CustomPredicate),
+    #[error(
+        "Not all statement templates of the following custom predicate have been matched:\n{0}"
+    )]
+    UnsatisfiedCustomPredicateConjunction(CustomPredicate),
+    #[error(
+        "None of the statement templates of the following custom predicate have been matched:\n{0}"
+    )]
+    UnsatisfiedCustomPredicateDisjunction(CustomPredicate),
     // Other
     #[error("{0}")]
     Custom(String),
@@ -65,6 +84,48 @@ impl Error {
     pub(crate) fn diff_amount(obj: String, unit: String, expect: usize, found: usize) -> Self {
         new!(DiffAmount(obj, unit, expect, found))
     }
+    pub(crate) fn invalid_wildcard_assignment(
+        wildcard: Wildcard,
+        value: Value,
+        prev_value: Value,
+    ) -> Self {
+        new!(InvalidWildcardAssignment(wildcard, value, prev_value))
+    }
+    pub(crate) fn mismatched_anchored_key_in_statement_tmpl_arg(
+        pod_id_wildcard: Wildcard,
+        pod_id: PodId,
+        key_tmpl: Key,
+        key: Key,
+    ) -> Self {
+        new!(MismatchedAnchoredKeyInStatementTmplArg(
+            pod_id_wildcard,
+            pod_id,
+            key_tmpl,
+            key
+        ))
+    }
+    pub(crate) fn mismatched_statement_tmpl_arg(
+        st_tmpl_arg: StatementTmplArg,
+        st_arg: StatementArg,
+    ) -> Self {
+        new!(MismatchedStatementTmplArg(st_tmpl_arg, st_arg))
+    }
+    pub(crate) fn mismatched_wildcard_value_and_statement_arg(
+        wc_value: Value,
+        st_arg: Value,
+        arg_index: usize,
+        pred: CustomPredicate,
+    ) -> Self {
+        new!(MismatchedWildcardValueAndStatementArg(
+            wc_value, st_arg, arg_index, pred
+        ))
+    }
+    pub(crate) fn unsatisfied_custom_predicate_conjunction(pred: CustomPredicate) -> Self {
+        new!(UnsatisfiedCustomPredicateConjunction(pred))
+    }
+    pub(crate) fn unsatisfied_custom_predicate_disjunction(pred: CustomPredicate) -> Self {
+        new!(UnsatisfiedCustomPredicateDisjunction(pred))
+    }
     pub(crate) fn custom(s: String) -> Self {
         new!(Custom(s))
     }

src/middleware/operation.rs

@@ -355,7 +355,7 @@ impl Operation {
             (Self::Custom(CustomPredicateRef { batch, index }, args), Custom(cpr, s_args))
                 if batch == &cpr.batch && index == &cpr.index =>
             {
-                check_custom_pred(params, cpr, args, s_args)?
+                check_custom_pred(params, cpr, args, s_args).map(|_| true)?
             }
             _ => return Err(deduction_err()),
         };
@@ -370,79 +370,88 @@ pub fn check_st_tmpl(
     st_arg: &StatementArg,
     // Map from wildcards to values that we have seen so far.
     wildcard_map: &mut [Option<Value>],
-) -> bool {
+) -> Result<()> {
     // Check that the value `v` at wildcard `wc` exists in the map or set it.
-    fn check_or_set(v: Value, wc: &Wildcard, wildcard_map: &mut [Option<Value>]) -> bool {
+    fn check_or_set(v: Value, wc: &Wildcard, wildcard_map: &mut [Option<Value>]) -> Result<()> {
         if let Some(prev) = &wildcard_map[wc.index] {
             if *prev != v {
-                // TODO: Return nice error
-                return false;
+                return Err(Error::invalid_wildcard_assignment(
+                    wc.clone(),
+                    v,
+                    prev.clone(),
+                ));
             }
         } else {
             wildcard_map[wc.index] = Some(v);
         }
-        true
+        Ok(())
     }
 
     match (st_tmpl_arg, st_arg) {
-        (StatementTmplArg::None, StatementArg::None) => true,
-        (StatementTmplArg::Literal(lhs), StatementArg::Literal(rhs)) if lhs == rhs => true,
+        (StatementTmplArg::None, StatementArg::None) => Ok(()),
+        (StatementTmplArg::Literal(lhs), StatementArg::Literal(rhs)) if lhs == rhs => Ok(()),
         (
             StatementTmplArg::AnchoredKey(pod_id_wc, key_tmpl),
             StatementArg::Key(AnchoredKey { pod_id, key }),
         ) => {
             let pod_id_ok = check_or_set(Value::from(*pod_id), pod_id_wc, wildcard_map);
-            pod_id_ok && (key_tmpl == key)
+            pod_id_ok.and_then(|_| {
+                (key_tmpl == key).then_some(()).ok_or(
+                    Error::mismatched_anchored_key_in_statement_tmpl_arg(
+                        pod_id_wc.clone(),
+                        *pod_id,
+                        key_tmpl.clone(),
+                        key.clone(),
+                    ),
+                )
+            })
         }
         (StatementTmplArg::Wildcard(wc), StatementArg::Literal(v)) => {
             check_or_set(v.clone(), wc, wildcard_map)
         }
-        _ => {
-            println!("DBG {:?} {:?}", st_tmpl_arg, st_arg);
-            false
-        }
+        _ => Err(Error::mismatched_statement_tmpl_arg(
+            st_tmpl_arg.clone(),
+            st_arg.clone(),
+        )),
     }
 }
 
 pub fn resolve_wildcard_values(
     params: &Params,
     pred: &CustomPredicate,
     args: &[Statement],
-) -> Option<Vec<Value>> {
+) -> Result<Vec<Value>> {
     // Check that all wildcard have consistent values as assigned in the statements while storing a
     // map of their values.
     // NOTE: We assume the statements have the same order as defined in the custom predicate.  For
     // disjunctions we expect Statement::None for the unused statements.
     let mut wildcard_map = vec![None; params.max_custom_predicate_wildcards];
     for (st_tmpl, st) in pred.statements.iter().zip(args) {
         let st_args = st.args();
-        for (st_tmpl_arg, st_arg) in st_tmpl.args.iter().zip(&st_args) {
-            if !check_st_tmpl(st_tmpl_arg, st_arg, &mut wildcard_map) {
-                // TODO: Better errors.  Example:
-                // println!("{} doesn't match {}", st_arg, st_tmpl_arg);
-                // println!("{} doesn't match {}", st, st_tmpl);
-                return None;
-            }
-        }
+        st_tmpl
+            .args
+            .iter()
+            .zip(&st_args)
+            .try_for_each(|(st_tmpl_arg, st_arg)| {
+                check_st_tmpl(st_tmpl_arg, st_arg, &mut wildcard_map)
+            })?;
     }
 
     // NOTE: We set unresolved wildcard slots with an empty value.  They can be unresolved because
     // they are beyond the number of used wildcards in this custom predicate, or they could be
     // private arguments that are unused in a particular disjunction.
-    Some(
-        wildcard_map
-            .into_iter()
-            .map(|opt| opt.unwrap_or(Value::from(0)))
-            .collect(),
-    )
+    Ok(wildcard_map
+        .into_iter()
+        .map(|opt| opt.unwrap_or(Value::from(0)))
+        .collect())
 }
 
 fn check_custom_pred(
     params: &Params,
     custom_pred_ref: &CustomPredicateRef,
     args: &[Statement],
     s_args: &[Value],
-) -> Result<bool> {
+) -> Result<()> {
     let pred = custom_pred_ref.predicate();
     if pred.statements.len() != args.len() {
         return Err(Error::diff_amount(
@@ -476,23 +485,33 @@ fn check_custom_pred(
         }
     }
 
-    let wildcard_map = match resolve_wildcard_values(params, pred, args) {
-        Some(wc_map) => wc_map,
-        None => return Ok(false),
-    };
+    let wildcard_map = resolve_wildcard_values(params, pred, args)?;
 
-    // Check that the resolved wildcard match the statement arguments.
-    for (s_arg, wc_value) in s_args.iter().zip(wildcard_map.iter()) {
+    // Check that the resolved wildcards match the statement arguments.
+    for (arg_index, (s_arg, wc_value)) in s_args.iter().zip(wildcard_map.iter()).enumerate() {
         if *wc_value != *s_arg {
-            return Ok(false);
+            return Err(Error::mismatched_wildcard_value_and_statement_arg(
+                wc_value.clone(),
+                s_arg.clone(),
+                arg_index,
+                pred.clone(),
+            ));
         }
     }
 
     if pred.conjunction {
-        Ok(num_matches == pred.statements.len())
-    } else {
-        Ok(num_matches > 0)
+        if num_matches != pred.statements.len() {
+            return Err(Error::unsatisfied_custom_predicate_conjunction(
+                pred.clone(),
+            ));
+        }
+    } else if num_matches == 0 {
+        return Err(Error::unsatisfied_custom_predicate_disjunction(
+            pred.clone(),
+        ));
     }
+
+    Ok(())
 }
 
 impl ToFields for Operation {