feat(frontends/lean/builtin_exprs): change how 'show' is processed in tactics

Unresolved placeholders were not being reported

hott/types/sigma.hlean

@@ -205,17 +205,16 @@ namespace sigma
     intro u,
     cases u with a b,
     apply (sigma_eq (left_inv f a)),
-    show transport B (left_inv f a) ((g (f⁻¹ (f a)))⁻¹ (transport B' (right_inv f (f a))⁻¹ (g a b))) = b,
+    calc
-    from calc
       transport B (left_inv f a) ((g (f⁻¹ (f a)))⁻¹ (transport B' (right_inv f (f a))⁻¹ (g a b)))
           = (g a)⁻¹ (transport (B' ∘ f) (left_inv f a) (transport B' (right_inv f (f a))⁻¹ (g a b)))
-              : by rewrite (fn_tr_eq_tr_fn (left_inv f a) (λ a, (g a)⁻¹))
+              : by esimp; rewrite (fn_tr_eq_tr_fn (left_inv f a) (λ a, (g a)⁻¹))
       ... = (g a)⁻¹ (transport B' (ap f (left_inv f a)) (transport B' (right_inv f (f a))⁻¹ (g a b)))
               : ap (g a)⁻¹ !transport_compose
       ... = (g a)⁻¹ (transport B' (ap f (left_inv f a)) (transport B' (ap f (left_inv f a))⁻¹ (g a b)))
            : ap (λ x, (g a)⁻¹ (transport B' (ap f (left_inv f a)) (transport B' x⁻¹ (g a b)))) (adj f a)
       ... = (g a)⁻¹ (g a b) : {!tr_inv_tr}
-      ... = b : by rewrite (left_inv (g a) b)
+      ... = b : by esimp; rewrite (left_inv (g a) b)
   end
 
   definition sigma_equiv_sigma_of_is_equiv [H1 : is_equiv f] [H2 : Π a, is_equiv (g a)]

src/frontends/lean/builtin_exprs.cpp

@@ -228,14 +228,9 @@ static expr parse_begin_end_core(parser & p, pos_info const & pos, name const &
                         throw parser_error("invalid 'have' tactic, 'by', 'begin', 'proof', or 'from' expected", p.pos());
                     }
                 }
-            } else if (p.curr_is_token(get_show_tk())) {
-                auto pos = p.pos();
-                expr t = p.parse_tactic_expr_arg();
-                t      = p.mk_app(get_rexact_tac_fn(), t, pos);
-                add_tac(t, pos);
             } else if (p.curr_is_token(get_match_tk()) || p.curr_is_token(get_assume_tk()) ||
                        p.curr_is_token(get_take_tk())  || p.curr_is_token(get_fun_tk()) ||
-                       p.curr_is_token(get_calc_tk())) {
+                       p.curr_is_token(get_calc_tk())  || p.curr_is_token(get_show_tk())) {
                 auto pos = p.pos();
                 expr t = p.parse_tactic_expr_arg();
                 t      = p.mk_app(get_exact_tac_fn(), t, pos);

tests/lean/show_tac.lean

@@ -0,0 +1,7 @@
+example (a b : Prop) : a ∧ b → b ∧ a :=
+begin
+  intro Hab,
+  have Ha : a, from and.elim_left  Hab,
+  have Hb : b, from and.elim_right Hab,
+  show b ∧ a, from and.intro _ Ha
+end

tests/lean/show_tac.lean.expected.out

@@ -0,0 +1,18 @@
+show_tac.lean:6:29: error: don't know how to synthesize placeholder
+a b : Prop,
+Hab : a ∧ b,
+Ha : a,
+Hb : b
+⊢ b
+show_tac.lean:6:2: error:invalid 'exact' tactic, term still contains metavariables after elaboration
+  show b ∧ a, from and.intro ?M_1 Ha
+proof state:
+a b : Prop,
+Hab : a ∧ b,
+Ha : a,
+Hb : b
+⊢ b ∧ a
+show_tac.lean:7:0: error: failed to add declaration '14.0' to environment, value has metavariables
+remark: set 'formatter.hide_full_terms' to false to see the complete term
+  λ (a b : Prop) (Hab : …),
+    ?M_1