relax unused block warning for duck typing

if a method `foo` uses a block, other (unrelated) method `foo`
can receives a block. So try to relax the unused block warning
condition.

```ruby
      class C0
        def f = yield
      end

      class C1 < C0
        def f = nil
      end

      [C0, C1].f{ block } # do not warn
```

1 files changed, 18 insertions, 5 deletions

diff --git a/compile.c b/compile.c
index b980d6a32c..853fadf5b0 100644
--- a/compile.c
+++ b/compile.c
@@ -1998,6 +1998,19 @@ iseq_set_arguments_keywords(rb_iseq_t *iseq, LINK_ANCHOR *const optargs,
     return arg_size;
 }
 
+static void
+iseq_set_use_block(rb_iseq_t *iseq)
+{
+    struct rb_iseq_constant_body *const body = ISEQ_BODY(iseq);
+    if (!body->param.flags.use_block) {
+        body->param.flags.use_block = 1;
+
+        rb_vm_t *vm = GET_VM();
+        st_data_t key = (st_data_t)rb_intern_str(body->location.label); // String -> ID
+        st_insert(vm->unused_block_warning_table, key, 1);
+    }
+}
+
 static int
 iseq_set_arguments(rb_iseq_t *iseq, LINK_ANCHOR *const optargs, const NODE *const node_args)
 {
@@ -2099,7 +2112,7 @@ iseq_set_arguments(rb_iseq_t *iseq, LINK_ANCHOR *const optargs, const NODE *cons
         if (block_id) {
             body->param.block_start = arg_size++;
             body->param.flags.has_block = TRUE;
-            body->param.flags.use_block = 1;
+            iseq_set_use_block(iseq);
         }
 
         iseq_calc_param_size(iseq);
@@ -5920,7 +5933,7 @@ defined_expr0(rb_iseq_t *iseq, LINK_ANCHOR *const ret,
         ADD_INSN(ret, line_node, putnil);
         ADD_INSN3(ret, line_node, defined, INT2FIX(DEFINED_YIELD), 0,
                   PUSH_VAL(DEFINED_YIELD));
-        ISEQ_BODY(ISEQ_BODY(iseq)->local_iseq)->param.flags.use_block = 1;
+        iseq_set_use_block(ISEQ_BODY(iseq)->local_iseq);
         return;
 
       case NODE_BACK_REF:
@@ -8632,7 +8645,7 @@ compile_builtin_attr(rb_iseq_t *iseq, const NODE *node)
             ISEQ_BODY(iseq)->builtin_attrs |= BUILTIN_ATTR_INLINE_BLOCK;
         }
         else if (strcmp(RSTRING_PTR(string), "use_block") == 0) {
-            ISEQ_BODY(iseq)->param.flags.use_block = 1;
+            iseq_set_use_block(iseq);
         }
         else {
             goto unknown_arg;
@@ -9481,7 +9494,7 @@ compile_super(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, i
     }
 
     if (use_block && parent_block == NULL) {
-        ISEQ_BODY(ISEQ_BODY(iseq)->local_iseq)->param.flags.use_block = 1;
+        iseq_set_use_block(ISEQ_BODY(iseq)->local_iseq);
     }
 
     flag |= VM_CALL_SUPER | VM_CALL_FCALL;
@@ -9527,7 +9540,7 @@ compile_yield(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, i
 
     ADD_SEQ(ret, args);
     ADD_INSN1(ret, node, invokeblock, new_callinfo(iseq, 0, FIX2INT(argc), flag, keywords, FALSE));
-    ISEQ_BODY(ISEQ_BODY(iseq)->local_iseq)->param.flags.use_block = 1;
+    iseq_set_use_block(ISEQ_BODY(iseq)->local_iseq);
 
     if (popped) {
         ADD_INSN(ret, node, pop);