[PRISM] Implement unused block warning

Related: ruby/prism#2935

iseq.c

@@ -1030,7 +1030,6 @@ pm_iseq_new_with_opt(pm_scope_node_t *node, VALUE name, VALUE path, VALUE realpa
 {
     rb_iseq_t *iseq = iseq_alloc();
     ISEQ_BODY(iseq)->prism = true;
-    ISEQ_BODY(iseq)->param.flags.use_block = true; // unused block warning is not supported yet
 
     rb_compile_option_t next_option;
     if (!option) option = &COMPILE_OPTION_DEFAULT;

prism_compile.c

@@ -3825,6 +3825,7 @@ pm_compile_defined_expr0(rb_iseq_t *iseq, const pm_node_t *node, const pm_node_l
       case PM_YIELD_NODE:
         PUSH_INSN(ret, location, putnil);
         PUSH_INSN3(ret, location, defined, INT2FIX(DEFINED_YIELD), 0, PUSH_VAL(DEFINED_YIELD));
+        iseq_set_use_block(ISEQ_BODY(iseq)->local_iseq);
         return;
       case PM_SUPER_NODE:
       case PM_FORWARDING_SUPER_NODE:
@@ -6962,6 +6963,9 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
 
             PUSH_LABEL(ret, retry_label);
         }
+        else {
+            iseq_set_use_block(ISEQ_BODY(iseq)->local_iseq);
+        }
 
         PUSH_INSN(ret, location, putself);
         int flag = VM_CALL_ZSUPER | VM_CALL_SUPER | VM_CALL_FCALL;
@@ -8994,6 +8998,7 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
             if (parameters_node->block) {
                 body->param.block_start = local_index;
                 body->param.flags.has_block = true;
+                iseq_set_use_block(iseq);
 
                 pm_constant_id_t name = ((const pm_block_parameter_node_t *) parameters_node->block)->name;
 
@@ -9549,6 +9554,10 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
             pm_scope_node_destroy(&next_scope_node);
         }
 
+        if (!cast->block) {
+            iseq_set_use_block(ISEQ_BODY(iseq)->local_iseq);
+        }
+
         if ((flags & VM_CALL_ARGS_BLOCKARG) && (flags & VM_CALL_KW_SPLAT) && !(flags & VM_CALL_KW_SPLAT_MUT)) {
             PUSH_INSN(args, location, splatkw);
         }
@@ -9681,6 +9690,7 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
         }
 
         PUSH_INSN1(ret, location, invokeblock, new_callinfo(iseq, 0, argc, flags, keywords, FALSE));
+        iseq_set_use_block(ISEQ_BODY(iseq)->local_iseq);
         if (popped) PUSH_INSN(ret, location, pop);
 
         int level = 0;

test/ruby/test_iseq.rb

@@ -887,8 +887,6 @@ class TestISeq < Test::Unit::TestCase
   def test_unused_param
     a = RubyVM::InstructionSequence.of(method(:block_using_method)).to_a
 
-    omit 'TODO: Prism' if a.dig(4, :parser) != :"parse.y"
-
     assert_equal true, a.dig(11, :use_block)
 
     b = RubyVM::InstructionSequence.of(method(:block_unused_method)).to_a