feat(frontends/lean/builtin_cmds): show metavariable arguments when pretty printing patterns

src/frontends/lean/builtin_cmds.cpp

@@ -240,7 +240,10 @@ static void print_patterns(parser & p, name const & n) {
             blast::scope_debug scope(p.env(), p.ios());
             auto hi = blast::mk_hi_lemma(n, LEAN_FORWARD_LEMMA_DEFAULT_PRIORITY);
             if (hi.m_multi_patterns) {
-                io_state_stream out = p.regular_stream();
+                io_state_stream _out = p.regular_stream();
+                options opts         = _out.get_options();
+                opts                 = opts.update_if_undef(get_pp_metavar_args_name(), true);
+                io_state_stream out  = _out.update_options(opts);
                 out << "(multi-)patterns:\n";
                 if (!is_nil(hi.m_mvars)) {
                     expr m = head(hi.m_mvars);

tests/lean/pattern_pp.lean

@@ -0,0 +1,11 @@
+definition Sum : nat → (nat → nat) → nat := sorry
+definition Sum_weird [forward] (f g h : nat → nat) (n : nat) : (Sum n (λ x, f (g (h x)))) = 1 := sorry
+print Sum_weird
+
+/-
+definition Sum_weird [forward] : ∀ (f g h : nat → nat) (n : nat), eq (Sum n (λ (x : nat), f (g (h x)))) 1 :=
+λ (f g h : nat → nat) (n : nat), sorry
+(multi-)patterns:
+?M_1 : nat → nat, ?M_2 : nat → nat, ?M_3 : nat → nat, ?M_4 : nat
+{Sum ?M_4 (λ (x : nat), ?M_1)}
+-/

tests/lean/pattern_pp.lean.expected.out

@@ -0,0 +1,5 @@
+definition Sum_weird [forward] : ∀ (f g h : ℕ → ℕ) (n : ℕ), Sum n (λ (x : ℕ), f (g (h x))) = 1 :=
+λ (f g h : ℕ → ℕ) (n : ℕ), sorry
+(multi-)patterns:
+?M_1 : ℕ → ℕ, ?M_2 : ℕ → ℕ, ?M_3 : ℕ → ℕ, ?M_4 : ℕ
+{Sum ?M_4 (λ (x : ℕ), ?M_1 (?M_2 (?M_3 x)))}