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Make Names section extensible (#984)
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* Make Names section extensible

* Fix typo

* Switch name list to name map and drop mention of UTF8

* Change  to
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lukewagner authored Feb 17, 2017
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63 changes: 48 additions & 15 deletions BinaryEncoding.md
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Expand Up @@ -436,34 +436,67 @@ The expectation is that, when a binary WebAssembly module is viewed in a browser
environment, the data in this section will be used as the names of functions
and locals in the [text format](TextFormat.md).

The name section contains a sequence of name subsections:

| Field | Type | Description |
| ----- | ---- | ----------- |
| count | `varuint32` | count of entries to follow |
| entries | `function_names*` | sequence of names |
| name_type | `varuint7` | code identifying type of name contained in this subsection |
| name_payload_len | `varuint32` | size of this subsection in bytes |
| name_payload_data | `bytes` | content of this section, of length `name_payload_len` |

The sequence of `function_names` assigns names to the corresponding
[function index](Modules.md#function-index-space). (Note: this assigns names to both
imported and module-defined functions.) The count may differ from the actual number of functions.
Since name subsections have a given length, unknown or unwanted names types can
be skipped over by an engine. The current list of valid `name_type` codes are:

#### Function names
| Name Type | Code | Description |
| --------- | ---- | ----------- |
| [Function](#function-names) | `1` | Assigns names to functions |
| [Local](#local-names) | `2` | Assigns names to locals in functions |

When present, name subsections must appear in this order and at most once. The
end of the last subsection must coincide with the last byte of the name
section to be a well-formed name section.

#### Name Map

In the following subsections, a `name_map` is encoded as:

| Field | Type | Description |
| ----- | ---- | ----------- |
| fun_name_len | `varuint32` | string length, in bytes |
| fun_name_str | `bytes` | valid utf8 encoding |
| local_count | `varuint32` | count of local names to follow |
| local_names | `local_name*` | sequence of local names |
| count | `varuint32` | number of `naming` in names |
| names | `naming*` | sequence of `naming` sorted by index |

The sequence of `local_name` assigns names to the corresponding local index. The
count may differ from the actual number of locals.
where a `naming` is encoded as:

#### Local name
| Field | Type | Description |
| ----- | ---- | ----------- |
| index | `varuint32` | the index which is being named |
| name_len | `varuint32` | number of bytes in name_str |
| name_str | `bytes` | binary encoding of the name |

#### Function names

The function names subsection is a `name_map` which assigns names to
a subset of the [function index space](Modules.md#function-index-space)
(both imports and module-defined).

#### Local names

The local names subsection assigns `name_map`s to a subset of functions in the
[function index space](Modules.md#function-index-space) (both imports and
module-defined). The `name_map` for a given function assigns names to a
subset of local variable indices.

| Field | Type | Description |
| ----- | ---- | ----------- |
| local_name_len | `varuint32` | string length, in bytes |
| local_name_str | `bytes` | valid utf8 encoding |
| count | `varuint32` | count of `local_names` in funcs |
| funcs | `local_names*` | sequence of `local_names` sorted by index |

where a `local_name` is encoded as:

| Field | Type | Description |
| ----- | ---- | ----------- |
| index | `varuint32` | the index of the function whose locals are being named |
| local_map | `name_map` | assignment of names to local indices |

# Function Bodies

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