inspect objects with "Symbol" attributes

[mmarchini]

Inspect commands can't handle Symbol attributes (e.g. @@toStringTag and @@unscopable), resulting in <non-string> properties.

For example, the following code uses the @@toStringTag symbol:

class Bar {
  constructor() {
    this[Symbol.toStringTag] = "Bar";
  }
}

let bar = new Bar();

If we use llnode to find out the properties for bar, it will give the following output:

(lldb) v8 findjsinstances -v Bar
0x0000015078184729:<Object: Bar properties {
    .constructor=0x00000150781846e1:<function: Bar at index.js:17:14>}>
0x0000015078184949:<Object: Bar properties {
    .<non-string>=0x00002d2064acb1e1:<String: "Bar">}>

As you can see, there's a <non-string> property instead of our symbol.

I was looking at llnode and V8 code to try to find a solution, but I'm not sure how to implement it. Did anyone try this before?

[bnoordhuis]

Can you try this patch with node.js master? That should add the metadata for symbols although llnode still needs to be taught to use it.

diff --git a/deps/v8/src/v8.gyp b/deps/v8/src/v8.gyp
index 89eb271f61..38670c193d 100644
--- a/deps/v8/src/v8.gyp
+++ b/deps/v8/src/v8.gyp
@@ -2452,6 +2452,8 @@
             'objects-inl.h',
             'objects/map.h',
             'objects/map-inl.h',
+            'objects/name.h',
+            'objects/name-inl.h',
             'objects/script.h',
             'objects/script-inl.h',
             'objects/shared-function-info.h',
diff --git a/deps/v8/tools/gen-postmortem-metadata.py b/deps/v8/tools/gen-postmortem-metadata.py
index 22f0afbef3..5f33fdebe9 100644
--- a/deps/v8/tools/gen-postmortem-metadata.py
+++ b/deps/v8/tools/gen-postmortem-metadata.py
@@ -417,15 +417,10 @@ def load_objects_from_file(objfilename, checktypes):
         # way around.
         #
         for type in types:
-                #
-                # Symbols and Strings are implemented using the same classes.
-                #
-                usetype = re.sub('SYMBOL_', 'STRING_', type);
-
                 #
                 # REGEXP behaves like REG_EXP, as in JS_REGEXP_TYPE => JSRegExp.
                 #
-                usetype = re.sub('_REGEXP_', '_REG_EXP_', usetype);
+                usetype = re.sub('_REGEXP_', '_REG_EXP_', type);
 
                 #
                 # Remove the "_TYPE" suffix and then convert to camel case,

That gives you these:

$ nm out/Release/node | grep -i v8dbg.*symbol
0000000101596d58 D _v8dbg_class_Symbol__flags__SMI
0000000101596d54 D _v8dbg_class_Symbol__name__Object
000000010159ece4 S _v8dbg_parent_Symbol__Name
0000000101596a50 D _v8dbg_type_Symbol__SYMBOL_TYPE

[mmarchini]

@bnoordhuis yes, this patch is enough on the V8 side. Will you submit a CL with these changes?

[mmarchini]

@bnoordhuis would you mind if I open a CL with these changes, or do you want to do it?