feat(frontends/lean): improve support for user defined tactics

src/frontends/lean/elaborator.cpp

@@ -617,7 +617,12 @@ expr elaborator::visit_app(expr const & e, constraint_seq & cs) {
     constraint_seq a_cs;
     expr d_type = binding_domain(f_type);
     if (d_type == get_tactic_expr_type()) {
-        expr r = mk_app(f, mk_tactic_expr(app_arg(e)), e.get_tag());
+        expr const & a = app_arg(e);
+        expr r;
+        if (is_local(a) && (mlocal_type(a) == get_tactic_expr_type() || m_in_equation_lhs))
+            r = mk_app(f, a, e.get_tag());
+        else
+            r = mk_app(f, mk_tactic_expr(a), e.get_tag());
         cs += f_cs + a_cs;
         return r;
     } else {

src/library/tactic/expr_to_tactic.cpp

@@ -99,7 +99,10 @@ bool is_tactic_expr(expr const & e) {
 
 expr const & get_tactic_expr_expr(expr const & e) {
     lean_assert(is_tactic_expr(e));
-    return macro_arg(e, 0);
+    expr const * it = &e;
+    while (is_tactic_expr(*it))
+        it = &macro_arg(*it, 0);
+    return *it;
 }
 
 void check_tactic_expr(expr const & e, char const * error_msg) {

tests/lean/run/def_tac.lean

@@ -0,0 +1,26 @@
+context
+  open tactic
+  definition cases_refl (e : expr) : tactic :=
+  cases e; apply rfl
+
+  definition cases_lst_refl : expr_list → tactic
+  | cases_lst_refl expr_list.nil        := apply rfl
+  | cases_lst_refl (expr_list.cons a l) := cases a; cases_lst_refl l
+
+  -- Similar to cases_refl, but make sure the argument is not an arbitrary expression.
+  definition eq_rec {A : Type} {a b : A} (e : a = b) : tactic :=
+  cases e; apply rfl
+end
+
+notation `cases_lst` l:(foldr `,` (h t, tactic.expr_list.cons h t) tactic.expr_list.nil) := cases_lst_refl l
+
+open prod
+theorem tst₁ (a : nat × nat) : (pr1 a, pr2 a) = a :=
+by cases_refl a
+
+theorem tst₂ (a b : nat × nat) (h₁ : pr₁ a = pr₁ b) (h₂ : pr₂ a = pr₂ b) : a = b :=
+by cases_lst a, b, h₁, h₂
+
+open nat
+theorem tst₃ (a b : nat) (h : a = b) : a + b = b + a :=
+by eq_rec h