[Lldb-commits] [lldb] [lldb] Introduce formatter bytecode version 2 ABI (PR #228589)

[Adrian Prantl via lldb-commits]

================
@@ -238,30 +240,40 @@ This is followed by one or more dictionary values that immediately follow each o
 - Length of the program (ULEB128)
 - The program bytecode
 
+### Calling conventions
+
+A record's version number (see [Embedding](#embedding)) also determines the calling convention of its methods. This includes how `self` (`this`) is represented.
+
+In **version 1** (legacy), `self` is a combination of the data stack after `@init` and `@update` run. Nothing constrains what shape `self` ends up in, it can be zero, one, or many values.
+
+In **version 2**, the runtime owns `self`, a `Dictionary` that starts out empty. The runtime passes the same `Dictionary` as the first argument to every method except `@summary`, followed by that method's own arguments (if any). Methods may modify `self` in place, and do not return it. The runtime keeps a reference, to ensure modifications are visible to subsequent method calls.
+
 The possible function signatures are:
 
 ```{eval-rst}
-=========  ========================= ==============================
-Signature    Mnemonic                Stack Effect
----------  ------------------------- ------------------------------
-  0x00      ``@summary``              ``(Object -> String)``
-  0x01      ``@init``                 ``(Object -> Object+)``
-  0x02      ``@get_num_children``     ``(Object+ -> UInt)``
-  0x03      ``@get_child_index``      ``(Object+ String -> UInt)``
-  0x04      ``@get_child_at_index``   ``(Object+ UInt -> Object)``
-  0x05      ``@get_value``            ``(Object+ -> String)``
-  0x06      ``@update``               ``(Object+ -> Object+)``
-=========  ========================= ==============================
+=========  ========================= ==============================================  ==============================================
+Signature    Mnemonic                Stack Effect (version 1)                       Stack Effect (version 2)
+---------  ------------------------- ----------------------------------------------  ----------------------------------------------
+  0x00      ``@summary``              ``(Object -> String)``                          ``(Object -> String)``
+  0x01      ``@init``                 ``(Object -> Object+)``                         ``(Dictionary Object -> )``
----------------
adrian-prantl wrote:

Why doesn't init leave the (modified) Dictionary on the stack? In version 1 the idea was that init produces the global state (dubbed "Object+") that gets passed into all other functions.

https://github.com/llvm/llvm-project/pull/228589