Avoid adding new unneeded names to blocks in text roundtripping (#4943)

Previously the wat parser would turn this input:

(block
  (nop)
)

into something like this:

(block $block17
  (nop)
)

It just added a name all the time, in case the block is referred to by an index
later even though it doesn't have a name.

This PR makes us rountrip more precisely by not adding such names: if there
was no name before, and there is no break by index, then do not add a name.

In addition, this will be useful for non-nullable locals since whether a block has
a name or not matters there. Like #4912, this makes us more regular in our
usage of block names.

1 files changed, 2 insertions, 4 deletions

diff --git a/test/heap-types.wast.fromBinary b/test/heap-types.wast.fromBinary
index 6c847ff69..803908b19 100644
--- a/test/heap-types.wast.fromBinary
+++ b/test/heap-types.wast.fromBinary
@@ -71,9 +71,7 @@
    (ref.null $struct.A)
   )
   (drop
-   (block $label$1 (result (ref null $struct.A))
-    (local.get $x)
-   )
+   (local.get $x)
   )
   (drop
    (if (result (ref null $struct.A))
@@ -83,7 +81,7 @@
    )
   )
   (drop
-   (loop $label$4 (result (ref null $struct.A))
+   (loop $label$3 (result (ref null $struct.A))
     (local.get $x)
    )
   )