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, 38 insertions, 42 deletions

diff --git a/test/wasm2js/labels.2asm.js b/test/wasm2js/labels.2asm.js
index c12eaf7b4..4841f82f1 100644
--- a/test/wasm2js/labels.2asm.js
+++ b/test/wasm2js/labels.2asm.js
@@ -116,56 +116,52 @@ function asmFunc(env) {
  function $7() {
   var i = 0;
   i = 0;
-  block : {
-   l : {
-    break l;
-   }
-   i = i + 1 | 0;
-   l1 : {
-    break l1;
-   }
-   i = i + 1 | 0;
-   l2 : {
-    break l2;
-   }
-   i = i + 1 | 0;
-   l3 : {
-    break l3;
-   }
-   i = i + 1 | 0;
-   l4 : {
-    break l4;
-   }
-   i = i + 1 | 0;
+  l : {
+   break l;
+  }
+  i = i + 1 | 0;
+  l1 : {
+   break l1;
+  }
+  i = i + 1 | 0;
+  l2 : {
+   break l2;
   }
+  i = i + 1 | 0;
+  l3 : {
+   break l3;
+  }
+  i = i + 1 | 0;
+  l4 : {
+   break l4;
+  }
+  i = i + 1 | 0;
   return i | 0;
  }
  
  function $8() {
   var i = 0;
   i = 0;
-  block : {
-   if_ : {
-    break if_;
-   }
-   i = i + 1 | 0;
-   if5 : {
-    break if5;
-   }
-   i = i + 1 | 0;
-   if6 : {
-    break if6;
-   }
-   i = i + 1 | 0;
-   if7 : {
-    break if7;
-   }
-   i = i + 1 | 0;
-   if8 : {
-    break if8;
-   }
-   i = i + 1 | 0;
+  if_ : {
+   break if_;
+  }
+  i = i + 1 | 0;
+  if5 : {
+   break if5;
+  }
+  i = i + 1 | 0;
+  if6 : {
+   break if6;
+  }
+  i = i + 1 | 0;
+  if7 : {
+   break if7;
+  }
+  i = i + 1 | 0;
+  if8 : {
+   break if8;
   }
+  i = i + 1 | 0;
   return i | 0;
  }