feat(frontends/lean/elaborator): include overload information in error messages

src/frontends/lean/elaborator.cpp

@@ -337,7 +337,27 @@ expr elaborator::visit_choice(expr const & e, optional<expr> const & t, constrai
                   name_generator const & /* ngen */) {
         return choose(std::make_shared<choice_expr_elaborator>(*this, ctx, full_ctx, meta, type, e));
     };
-    justification j = mk_justification("none of the overloads is applicable", some_expr(e));
+    auto pp_fn = [=](formatter const & fmt, pos_info_provider const * pos_prov, substitution const &, bool is_main) {
+        format r = pp_previous_error_header(fmt, pos_prov, some_expr(e), is_main);
+        r += format("none of the overloads is applicable:");
+        for (unsigned i = 0; i < get_num_choices(e); i++) {
+            expr const & c = get_choice(e, i);
+            expr const & f = get_app_fn(c);
+            optional<name> fn;
+            if (is_constant(f))
+                fn = const_name(f);
+            else if (is_local(f))
+                fn = local_pp_name(f);
+            r += space();
+            if (fn) {
+                r += format(*fn);
+            } else {
+                r += format("[nontrivial]");
+            }
+        }
+        return r;
+    };
+    justification j = mk_justification(some_expr(e), pp_fn);
     cs += mk_choice_cnstr(m, fn, to_delay_factor(cnstr_group::Basic), true, j);
     return m;
 }
@@ -1158,7 +1178,9 @@ expr elaborator::visit_equations(expr const & eqns, constraint_seq & cs) {
         new_cs.linearize(tmp_cs);
         for (constraint const & c : tmp_cs) {
             justification j = c.get_justification();
-            auto pp_fn      = [=](formatter const & fmt, pos_info_provider const * pp, substitution const & s) {
+            auto pp_fn      = [=](formatter const & fmt, pos_info_provider const * pp, substitution const & s, bool is_main) {
+                if (!is_main)
+                    return format();
                 format r = j.pp(fmt, pp, s);
                 r += compose(line(), format("The following identifier(s) are introduced as free variables by the "
                                             "left-hand-side of the equation:"));

src/kernel/justification.cpp

@@ -6,6 +6,7 @@ Author: Leonardo de Moura
 */
 #include <string>
 #include <vector>
+#include <unordered_set>
 #include "util/buffer.h"
 #include "util/int64.h"
 #include "util/memory_pool.h"
@@ -26,6 +27,18 @@ format to_pos(optional<expr> const & e, pos_info_provider const * p) {
     return f + space();
 }
 
+format pp_previous_error_header(formatter const &, pos_info_provider const * pos_prov, optional<expr> const & ref, bool is_main) {
+    if (!is_main) {
+        format r = line();
+        r += to_pos(ref, pos_prov);
+        r += format("previous error additional information");
+        r += line();
+        return r;
+    } else {
+        return format();
+    }
+}
+
 typedef uint64 approx_set;
 static approx_set mk_empty_set() { return 0; }
 static approx_set mk_union(approx_set s1, approx_set s2) { return s1 | s2; }
@@ -263,23 +276,50 @@ optional<expr> justification::get_main_expr() const {
         }
     }
 }
-format justification::pp(formatter const & fmt, pos_info_provider const * p, substitution const & s) const {
+
+struct jst_hash_fn {
+    unsigned operator()(justification const & j) const { return j.raw()->m_hash_alloc; }
+};
+
+struct jst_ptr_eq {
+    bool operator()(justification const & j1, justification const & j2) const { return j1.raw() == j2.raw(); }
+};
+
+class justification_set {
+    std::unordered_set<justification, jst_hash_fn, jst_ptr_eq> m_set;
+public:
+    bool contains(justification const & j) const { return m_set.find(j) != m_set.end(); }
+    void insert(justification const & j) { m_set.insert(j); }
+};
+
+format justification::pp_core(formatter const & fmt, pos_info_provider const * p, substitution const & s,
+                              justification_set & set, bool is_main) const {
+    if (set.contains(*this))
+        return format();
+    set.insert(*this);
     justification_cell * it = m_ptr;
-    while (true) {
     if (!it)
         return format();
     switch (it->m_kind) {
     case justification_kind::Asserted:
-            return to_asserted(it)->m_fn(fmt, p, s);
+        return to_asserted(it)->m_fn(fmt, p, s, is_main);
     case justification_kind::Wrapper:
-            return to_wrapper(it)->m_fn(fmt, p, s);
+        return to_wrapper(it)->m_fn(fmt, p, s, is_main);
     case justification_kind::Assumption:
+        if (is_main)
             return format(format("Assumption "), format(to_assumption(it)->m_idx));
+        else
+            return format();
     case justification_kind::Composite:
-            it = to_composite(it)->m_child[0].raw();
-            break;
+        return
+            to_composite(it)->m_child[0].pp_core(fmt, p, s, set, is_main) +
+            to_composite(it)->m_child[1].pp_core(fmt, p, s, set, false);
     }
 }
+
+format justification::pp(formatter const & fmt, pos_info_provider const * p, substitution const & s) const {
+    justification_set set;
+    return pp_core(fmt, p, s, set, true);
 }
 
 justification mk_wrapper(justification const & j, optional<expr> const & s, pp_jst_fn const & fn) {
@@ -305,16 +345,22 @@ justification mk_justification(optional<expr> const & s, pp_jst_fn const & fn) {
     return justification(new (get_asserted_allocator().allocate()) asserted_cell(fn, s));
 }
 justification mk_justification(optional<expr> const & s, pp_jst_sfn const & fn) {
-    return mk_justification(s, [=](formatter const & fmt, pos_info_provider const *, substitution const & subst) {
+    return mk_justification(s, [=](formatter const & fmt, pos_info_provider const *, substitution const & subst, bool is_main) {
             // Remark: we are not using to_pos(s, p) anymore because we don't try to display complicated error messages anymore.
             // return compose(to_pos(s, p), fn(fmt, subst));
+            if (is_main)
                 return fn(fmt, subst);
+            else
+                return format();
         });
 }
 justification mk_justification(char const * msg, optional<expr> const & s) {
     std::string _msg(msg);
-    return mk_justification(s, [=](formatter const &, pos_info_provider const *, substitution const &) {
+    return mk_justification(s, [=](formatter const &, pos_info_provider const *, substitution const &, bool is_main) {
+            if (is_main)
                 return format(_msg);
+            else
+                return format();
         });
 }
 std::ostream & operator<<(std::ostream & out, justification const & j) {

src/kernel/justification.h

@@ -23,7 +23,9 @@ struct justification_cell;
    The pp_jst_fn is a generic funciton that produces these messages. We can associate these functions
    to justification objects.
 */
-typedef std::function<format(formatter const &, pos_info_provider const *, substitution const &)> pp_jst_fn;
+typedef std::function<format(formatter const &, pos_info_provider const *, substitution const &, bool)> pp_jst_fn;
+
+class justification_set;
 
 /**
     \brief Objects used to justify unification (and level) constraints and metavariable assignments.
@@ -40,6 +42,8 @@ typedef std::function<format(formatter const &, pos_info_provider const *, subst
 class justification {
     justification_cell * m_ptr;
     justification(justification_cell * ptr);
+    format pp_core(formatter const & fmt, pos_info_provider const * p, substitution const & s,
+                   justification_set & visited, bool is_main) const;
 public:
     justification();
     justification(justification const & s);
@@ -85,6 +89,7 @@ typedef std::function<format(formatter const &, substitution const &)> pp_jst_sf
 
 /** \brief Return a format object containing position information for the given expression (if available) */
 format to_pos(optional<expr> const & e, pos_info_provider const * p);
+format pp_previous_error_header(formatter const &, pos_info_provider const * pos_prov, optional<expr> const & ref, bool is_main);
 
 /** \brief Provide a custom pretty printer for \c j */
 justification mk_wrapper(justification const & j, optional<expr> const & s, pp_jst_fn const & fn);

tests/lean/subset_error.lean

@@ -0,0 +1,19 @@
+constant set    : Type₁ → Type₁
+constant finset : Type₁ → Type₁
+constant set.mem : Π {A : Type₁}, A → set A → Prop
+constant finset.mem : Π {A : Type₁}, A → finset A → Prop
+
+infix ∈ := set.mem
+infix ∈ := finset.mem
+
+definition set.subset {A : Type₁} (s₁ s₂ : set A) : Prop :=
+∀ ⦃a : A⦄, a ∈ s₁ → a ∈ s₂
+
+definition finset.subset {A : Type₁} (s₁ s₂ : finset A) : Prop :=
+∀ ⦃a : A⦄, a ∈ s₁ → a ∈ s₂
+
+infix `⊆`:50 := set.subset
+infix `⊆`:50 := finset.subset
+
+example (A : Type₁) (x : A) (S H : set A) (Pin : x ∈ S) (Psub : S ⊆ H) : x ∈ H :=
+Psub Pin -- Error, we cannot infer at preprocessing time the binder information for Psub

tests/lean/subset_error.lean.expected.out

@@ -0,0 +1,12 @@
+subset_error.lean:18:51: error: type mismatch at application
+  x ∈ S
+term
+  S
+has type
+  set A
+but is expected to have type
+  finset A
+subset_error.lean:18:51: previous error additional information
+none of the overloads is applicable: finset.mem set.mem
+subset_error.lean:18:66: previous error additional information
+none of the overloads is applicable: finset.subset set.subset