ADT recursion

Author: Grant Wuerker

Diff for: crates/hir-analysis/src/lib.rs

@@ -72,6 +72,7 @@ pub struct Jar(
     ty::diagnostics::ImplTraitDefDiagAccumulator,
     ty::diagnostics::ImplDefDiagAccumulator,
     ty::diagnostics::FuncDefDiagAccumulator,
+    ty::diagnostics::AdtRecursionConstituentAccumulator,
 );
 
 pub trait HirAnalysisDb: salsa::DbWithJar<Jar> + HirDb {

Diff for: crates/hir-analysis/src/ty/def_analysis.rs

@@ -21,7 +21,10 @@ use super::{
         collect_impl_block_constraints, collect_super_traits, AssumptionListId, SuperTraitCycle,
     },
     constraint_solver::{is_goal_satisfiable, GoalSatisfiability},
-    diagnostics::{ImplDiag, TraitConstraintDiag, TraitLowerDiag, TyDiagCollection, TyLowerDiag},
+    diagnostics::{
+        AdtRecursionConstituent, ImplDiag, TraitConstraintDiag, TraitLowerDiag, TyDiagCollection,
+        TyLowerDiag,
+    },
     trait_def::{ingot_trait_env, Implementor, TraitDef, TraitMethod},
     trait_lower::{lower_trait, lower_trait_ref, TraitRefLowerError},
     ty_def::{AdtDef, AdtRef, AdtRefId, FuncDef, InvalidCause, TyData, TyId},
@@ -32,8 +35,9 @@ use crate::{
     name_resolution::{resolve_path_early, EarlyResolvedPath, NameDomain, NameResKind},
     ty::{
         diagnostics::{
-            AdtDefDiagAccumulator, FuncDefDiagAccumulator, ImplDefDiagAccumulator,
-            ImplTraitDefDiagAccumulator, TraitDefDiagAccumulator, TypeAliasDefDiagAccumulator,
+            AdtDefDiagAccumulator, AdtRecursionConstituentAccumulator, FuncDefDiagAccumulator,
+            ImplDefDiagAccumulator, ImplTraitDefDiagAccumulator, TraitDefDiagAccumulator,
+            TypeAliasDefDiagAccumulator,
         },
         method_table::collect_methods,
         trait_lower::lower_impl_trait,
@@ -62,8 +66,8 @@ pub fn analyze_adt(db: &dyn HirAnalysisDb, adt_ref: AdtRefId) {
         AdtDefDiagAccumulator::push(db, diag);
     }
 
-    if let Some(diag) = check_recursive_adt(db, adt_ref) {
-        AdtDefDiagAccumulator::push(db, diag);
+    if let Some(constituent) = check_recursive_adt(db, adt_ref) {
+        AdtRecursionConstituentAccumulator::push(db, constituent);
     }
 }
 
@@ -764,7 +768,7 @@ impl<'db> Visitor for DefAnalyzer<'db> {
 pub(crate) fn check_recursive_adt(
     db: &dyn HirAnalysisDb,
     adt: AdtRefId,
-) -> Option<TyDiagCollection> {
+) -> Option<AdtRecursionConstituent> {
     let adt_def = lower_adt(db, adt);
     for field in adt_def.fields(db) {
         for ty in field.iter_types(db) {
@@ -781,7 +785,7 @@ fn check_recursive_adt_impl(
     db: &dyn HirAnalysisDb,
     cycle: &salsa::Cycle,
     adt: AdtRefId,
-) -> Option<TyDiagCollection> {
+) -> Option<AdtRecursionConstituent> {
     let participants: FxHashSet<_> = cycle
         .participant_keys()
         .map(|key| check_recursive_adt::key_from_id(key.key_index()))
@@ -792,11 +796,14 @@ fn check_recursive_adt_impl(
         for (ty_idx, ty) in field.iter_types(db).enumerate() {
             for field_adt_ref in ty.collect_direct_adts(db) {
                 if participants.contains(&field_adt_ref) && participants.contains(&adt) {
-                    let diag = TyLowerDiag::recursive_type(
-                        adt.name_span(db),
-                        adt_def.variant_ty_span(db, field_idx, ty_idx),
+                    let constituent = AdtRecursionConstituent::new(
+                        (adt, adt.name_span(db)),
+                        (
+                            field_adt_ref,
+                            adt_def.variant_ty_span(db, field_idx, ty_idx),
+                        ),
                     );
-                    return Some(diag.into());
+                    return Some(constituent);
                 }
             }
         }

Diff for: crates/hir-analysis/src/ty/diagnostics.rs

@@ -10,12 +10,14 @@ use hir::{
     HirDb, SpannedHirDb,
 };
 use itertools::Itertools;
+use rustc_hash::FxHashSet;
+
+use crate::HirAnalysisDb;
 
 use super::{
     constraint::PredicateId,
-    ty_def::{Kind, TyId},
+    ty_def::{AdtRefId, Kind, TyId},
 };
-use crate::HirAnalysisDb;
 
 #[salsa::accumulator]
 pub struct AdtDefDiagAccumulator(pub(super) TyDiagCollection);
@@ -29,6 +31,8 @@ pub struct ImplDefDiagAccumulator(pub(super) TyDiagCollection);
 pub struct FuncDefDiagAccumulator(pub(super) TyDiagCollection);
 #[salsa::accumulator]
 pub struct TypeAliasDefDiagAccumulator(pub(super) TyDiagCollection);
+#[salsa::accumulator]
+pub struct AdtRecursionConstituentAccumulator(pub(super) AdtRecursionConstituent);
 
 #[derive(Debug, PartialEq, Eq, Hash, Clone, derive_more::From)]
 pub enum TyDiagCollection {
@@ -53,10 +57,7 @@ impl TyDiagCollection {
 pub enum TyLowerDiag {
     ExpectedStarKind(DynLazySpan),
     InvalidTypeArgKind(DynLazySpan, String),
-    RecursiveType {
-        primary_span: DynLazySpan,
-        field_span: DynLazySpan,
-    },
+    AdtRecursion(Vec<AdtRecursionConstituent>),
 
     UnboundTypeAliasParam {
         span: DynLazySpan,
@@ -140,11 +141,8 @@ impl TyLowerDiag {
         Self::InvalidTypeArgKind(span, msg)
     }
 
-    pub(super) fn recursive_type(primary_span: DynLazySpan, field_span: DynLazySpan) -> Self {
-        Self::RecursiveType {
-            primary_span,
-            field_span,
-        }
+    pub(super) fn adt_recursion(constituents: Vec<AdtRecursionConstituent>) -> Self {
+        Self::AdtRecursion(constituents)
     }
 
     pub(super) fn unbound_type_alias_param(
@@ -249,7 +247,7 @@ impl TyLowerDiag {
         match self {
             Self::ExpectedStarKind(_) => 0,
             Self::InvalidTypeArgKind(_, _) => 1,
-            Self::RecursiveType { .. } => 2,
+            Self::AdtRecursion { .. } => 2,
             Self::UnboundTypeAliasParam { .. } => 3,
             Self::TypeAliasCycle { .. } => 4,
             Self::InconsistentKindBound(_, _) => 5,
@@ -270,7 +268,7 @@ impl TyLowerDiag {
         match self {
             Self::ExpectedStarKind(_) => "expected `*` kind in this context".to_string(),
             Self::InvalidTypeArgKind(_, _) => "invalid type argument kind".to_string(),
-            Self::RecursiveType { .. } => "recursive type is not allowed".to_string(),
+            Self::AdtRecursion { .. } => "recursive type is not allowed".to_string(),
 
             Self::UnboundTypeAliasParam { .. } => {
                 "all type parameters of type alias must be given".to_string()
@@ -326,22 +324,23 @@ impl TyLowerDiag {
                 span.resolve(db),
             )],
 
-            Self::RecursiveType {
-                primary_span,
-                field_span,
-            } => {
-                vec![
-                    SubDiagnostic::new(
+            Self::AdtRecursion(constituents) => {
+                let mut diags = vec![];
+
+                for AdtRecursionConstituent { from, to } in constituents {
+                    diags.push(SubDiagnostic::new(
                         LabelStyle::Primary,
                         "recursive type definition".to_string(),
-                        primary_span.resolve(db),
-                    ),
-                    SubDiagnostic::new(
+                        from.1.resolve(db),
+                    ));
+                    diags.push(SubDiagnostic::new(
                         LabelStyle::Secondary,
                         "recursion occurs here".to_string(),
-                        field_span.resolve(db),
-                    ),
-                ]
+                        to.1.resolve(db),
+                    ));
+                }
+
+                diags
             }
 
             Self::UnboundTypeAliasParam {
@@ -1260,3 +1259,64 @@ impl DiagnosticVoucher for ImplDiag {
         CompleteDiagnostic::new(severity, message, sub_diags, vec![], error_code)
     }
 }
+
+/// Generates diagnostics from a list of ADT recursion constituents.
+pub fn adt_recursion_diags(constituents: &[AdtRecursionConstituent]) -> Vec<TyDiagCollection> {
+    let mut diags = vec![];
+
+    // `unified_constituents` tracks constituents that have been included in recursions.
+    // Constituents in this set cannot be used to construct other recursions.
+    let mut unified_constituents = FxHashSet::default();
+
+    // `cur` is set to the first item in `constituents` that has not been included in another recursion.
+    while let Some(mut cur) =
+        (0..constituents.len()).find(|index| !unified_constituents.contains(index))
+    {
+        unified_constituents.insert(cur);
+        let mut recursion = vec![cur];
+
+        // The recursion is complete if the `from` of the first constituent is equal to the `to` of `cur`.
+        while constituents[recursion[0]].from.0 != constituents[cur].to.0 {
+            // The next constituent of the recursion is found by comparing the `to` of `cur` with `from` of the candidate constituent.
+            if let Some(index) = (0..constituents.len()).find(|index| {
+                !unified_constituents.contains(index)
+                    && constituents[cur].to.0 == constituents[*index].from.0
+            }) {
+                cur = index;
+                unified_constituents.insert(index);
+                recursion.push(index);
+            } else {
+                break;
+            };
+        }
+
+        diags.push(
+            TyLowerDiag::adt_recursion(
+                recursion
+                    .iter()
+                    .map(|index| constituents[*index].to_owned())
+                    .collect(),
+            )
+            .into(),
+        );
+    }
+
+    diags
+}
+
+/// Constituent of an ADT recursion.
+///
+/// A full ADT recursion can be represented using a list of `AdtRecursionConstituent`s.
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
+pub struct AdtRecursionConstituent {
+    /// The ADT definition from which the constituent originates and its name span.
+    pub from: (AdtRefId, DynLazySpan),
+    /// The ADT to which this recursion continues and the span where this occurs
+    pub to: (AdtRefId, DynLazySpan),
+}
+
+impl AdtRecursionConstituent {
+    pub fn new(from: (AdtRefId, DynLazySpan), to: (AdtRefId, DynLazySpan)) -> Self {
+        Self { from, to }
+    }
+}

Diff for: crates/hir-analysis/src/ty/mod.rs

@@ -1,13 +1,15 @@
 use hir::{analysis_pass::ModuleAnalysisPass, hir_def::TopLevelMod};
+use itertools::Itertools;
 
 use self::{
     def_analysis::{
         analyze_adt, analyze_func, analyze_impl, analyze_impl_trait, analyze_trait,
         analyze_type_alias,
     },
     diagnostics::{
-        AdtDefDiagAccumulator, FuncDefDiagAccumulator, ImplDefDiagAccumulator,
-        ImplTraitDefDiagAccumulator, TraitDefDiagAccumulator, TypeAliasDefDiagAccumulator,
+        adt_recursion_diags, AdtDefDiagAccumulator, AdtRecursionConstituentAccumulator,
+        FuncDefDiagAccumulator, ImplDefDiagAccumulator, ImplTraitDefDiagAccumulator,
+        TraitDefDiagAccumulator, TypeAliasDefDiagAccumulator,
     },
     ty_def::AdtRefId,
 };
@@ -61,12 +63,26 @@ impl<'db> ModuleAnalysisPass for TypeDefAnalysisPass<'db> {
                     .iter()
                     .map(|c| AdtRefId::from_contract(self.db, *c)),
             );
+        let (diags, recursion_constituents): (Vec<_>, Vec<_>) = adts
+            .map(|adt| {
+                (
+                    analyze_adt::accumulated::<AdtDefDiagAccumulator>(self.db, adt),
+                    analyze_adt::accumulated::<AdtRecursionConstituentAccumulator>(self.db, adt),
+                )
+            })
+            .unzip();
+        let recursion_constituents = recursion_constituents.into_iter().flatten().collect_vec();
 
-        adts.flat_map(|adt| {
-            analyze_adt::accumulated::<AdtDefDiagAccumulator>(self.db, adt).into_iter()
-        })
-        .map(|diag| diag.to_voucher())
-        .collect()
+        diags
+            .into_iter()
+            .flatten()
+            .map(|diag| diag.to_voucher())
+            .chain(
+                adt_recursion_diags(&recursion_constituents)
+                    .iter()
+                    .map(|diag| diag.to_voucher()),
+            )
+            .collect()
     }
 }
 

Diff for: crates/uitest/fixtures/ty/def/recursive_type.snap

@@ -1,7 +1,7 @@
 ---
 source: crates/uitest/tests/ty.rs
 expression: diags
-input_file: crates/uitest/fixtures/ty/recursive_type.fe
+input_file: crates/uitest/fixtures/ty/def/recursive_type.fe
 ---
 error[3-0002]: recursive type is not allowed
   ┌─ recursive_type.fe:1:12
@@ -12,24 +12,18 @@ error[3-0002]: recursive type is not allowed
   │        -- recursion occurs here
 
 error[3-0002]: recursive type is not allowed
-  ┌─ recursive_type.fe:5:12
-  │
-5 │ pub struct S2 {
-  │            ^^ recursive type definition
-6 │     s: S3
-  │        -- recursion occurs here
-
-error[3-0002]: recursive type is not allowed
-   ┌─ recursive_type.fe:9:12
+   ┌─ recursive_type.fe:5:12
    │
+ 5 │ pub struct S2 {
+   │            ^^ recursive type definition
+ 6 │     s: S3
+   │        -- recursion occurs here
+   ·
  9 │ pub struct S3 {
    │            ^^ recursive type definition
 10 │     s: S4
    │        -- recursion occurs here
-
-error[3-0002]: recursive type is not allowed
-   ┌─ recursive_type.fe:13:12
-   │
+   ·
 13 │ pub struct S4 {
    │            ^^ recursive type definition
 14 │     s: S2