feat(frontends/lean/elaborator): restrict the number of places where coercions are considered

We do not consider coercions around meta-variables anymore.

hott/algebra/category/functor/yoneda.hlean

@@ -50,7 +50,7 @@ namespace yoneda
   end
 
   definition yoneda_lemma_equiv [constructor] {C : Precategory} (c : C)
-    (F : Cᵒᵖ ⇒ cset) : hom (ɏ c) F ≃ lift (F c) :=
+    (F : Cᵒᵖ ⇒ cset) : hom (ɏ c) F ≃ lift (trunctype.carrier (to_fun_ob F c)) :=
   begin
     fapply equiv.MK,
     { intro η, exact up (η c id)},

library/data/rat/basic.lean

@@ -360,10 +360,10 @@ definition of_num [coercion] [reducible] (n : num) : ℚ := num.to.rat n
 protected definition prio := num.pred int.prio
 
 definition rat_has_zero [reducible] [instance] [priority rat.prio] : has_zero rat :=
-has_zero.mk (0:int)
+has_zero.mk (of_int 0)
 
 definition rat_has_one [reducible] [instance] [priority rat.prio] : has_one rat :=
-has_one.mk (1:int)
+has_one.mk (of_int 1)
 
 theorem of_int_zero : of_int (0:int) = (0:rat) :=
 rfl

library/data/real/basic.lean

@@ -1098,10 +1098,10 @@ definition of_nat [coercion] (n : ℕ) : ℝ := nat.to.real n
 definition of_num [coercion] [reducible] (n : num) : ℝ := of_rat (rat.of_num n)
 
 definition real_has_zero [reducible] [instance] [priority real.prio] : has_zero real :=
-has_zero.mk (0:rat)
+has_zero.mk (of_rat 0)
 
 definition real_has_one [reducible] [instance] [priority real.prio] : has_one real :=
-has_one.mk (1:rat)
+has_one.mk (of_rat 1)
 
 theorem real_zero_eq_rat_zero : (0:real) = of_rat (0:rat) :=
 rfl

src/frontends/lean/elaborator.cpp

@@ -616,7 +616,7 @@ pair<expr, constraint_seq> elaborator::mk_delayed_coercion(
 pair<expr, constraint_seq> elaborator::ensure_has_type_core(
     expr const & a, expr const & a_type, expr const & expected_type, bool use_expensive_coercions, justification const & j) {
     bool lifted_coe = false;
-    if (m_ctx.m_coercions) {
+    if (m_ctx.m_coercions && !is_meta(a)) {
         if (use_expensive_coercions &&
             has_coercions_from(a_type, lifted_coe) && ((!lifted_coe && is_meta(expected_type)) || (lifted_coe && is_pi_meta(expected_type)))) {
             return mk_delayed_coercion(a, a_type, expected_type, j);

tests/lean/run/coe_issue2.lean

@@ -0,0 +1,8 @@
+import data.int data.real
+open int real
+
+example : (1 : ℤ) * (1 : ℤ) = (1 : ℤ) :=
+sorry
+
+example : (1 : ℤ) * 1 = 1 :=
+sorry

tests/lean/run/coe_issue3.lean

@@ -0,0 +1,24 @@
+import data.int data.real
+open algebra nat int rat real
+
+example : (1 : ℤ) * (1 : ℤ) = (1 : ℤ) :=
+sorry
+
+example : (1 : ℤ) * 1 = 1 :=
+sorry
+
+example : (1 : ℝ) * (1 : ℝ) = (1 : ℝ) :=
+sorry
+
+example : (1 : ℝ) * 1 = 1 :=
+sorry
+
+variable x : ℝ
+variable a : ℤ
+variable n : ℕ
+
+example : x + a + n + 1 = 1 :=
+sorry
+
+example : x + 1 = 1 + x :=
+sorry