SamandClaude Fable 5.1
23c14aaec1
The notes and comments say what is true of the 1.12.1 client and cite the byte address; the record numbers, the dates and the private repository's file paths go. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
84 lines
5.3 KiB
Markdown
84 lines
5.3 KiB
Markdown
# benilla's `lua-src` fork: what differs from upstream, and how to check
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Upstream: [`mlua-rs/lua-src-rs`](https://github.com/mlua-rs/lua-src-rs), MIT, version `550.0.0`,
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the version mlua 0.11 resolves to. Wired in through `[patch.crates-io]` in the workspace root.
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## Why a fork exists at all
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benilla's Lua has to accept exactly the grammar the 1.12.1 client's Lua accepts, no more and no
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less. Every hunk below is that one rule: three restore 5.0 constructs 5.1 deleted, three delete 5.1
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constructs 5.0 never had. A grammar difference in either direction is invisible to every instrument
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until an addon trips over it, and the addon corpus asks about the difference directly.
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The 1.12 addon corpus is Lua 5.0 code. It uses the iterator-less generic-for:
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```lua
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for k, v in someTable do ... end -- no pairs(), no iterator function
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```
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183 of 218 corpus addons are reached by it (118 carry it, 65 inherit it through a declared
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dependency), across 1,163 sites. On stock Lua 5.1 it raises `attempt to call a table value`, the
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first session-start error for 60 of the 218.
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Lua 5.1 removed it at the opcode level, which is why no layer above the VM can reach it: a `__call`
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metamethod would need a per-type default metatable for tables, which 5.1 does not have; rewriting
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the chunk source means parsing Lua with a regex; and `lua-src` ships 5.1 through 5.5, every one of
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which removed it.
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## What is not being done
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benilla is not adopting Lua 5.0. It stays on 5.1.5 and restores the behaviour of a single opcode
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that Lua itself shipped and labelled `/* for compatibility only */`. Every other 5.1 fix, and the
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whole of mlua's surface, stay exactly as upstream.
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## The delta, and the command that proves it
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Eight hunks in three files. `src/lib.rs` additionally differs by having Lua 5.2/5.3/5.4/5.5 stripped
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from the `Version` enum (with their source trees deleted): benilla builds 5.1 and only 5.1, and a
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fork that still offered the other four would answer a request for one with a missing directory at
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build time instead of a compile error.
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Five hunks restore what 5.1 changed or removed:
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| file | hunk | why |
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|---|---|---|
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| `lvm.c` | 5.0's `OP_TFORPREP` table-to-`next` substitution, folded into the top of `OP_TFORLOOP` | `for k, v in someTable do` raised "attempt to call a table value" |
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| `luaconf.h` | `LUA_COMPAT_LSTR` `1` to `2` | 5.1 kept 5.0's `[[...]]` nesting machinery and put an advisory error in front of it; two corpus addons died on "nesting of `[[...]]` is deprecated" |
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| `luaconf.h` | `LUA_QL(x)` back to 5.0's `` `x' `` from 5.1's `'x'` | every Lua error message quotes a program element, and `WoW.exe`'s own `.rdata` carries all five formats in the 5.0 spelling |
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| `lparser.c` | 5.0's compat-semicolon skip restored at the top of `constructor()`'s field loop, 5.0's own line verbatim | one extra `;` after a field separator inside a table constructor (`Back_Title = AL["Factions"];;`, which AtlasLoot writes) is accepted by the client and was a parse error here |
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| `lparser.c` | `recfield`'s `cc->nh++` moved back inside its `TK_NAME` arm, 5.0's own placement | a `[expr] = value` constructor field credits neither `OP_NEWTABLE` size hint in 5.0, so the table is born on the dummy node |
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Three delete what 5.1 added, all in `lparser.c`, all byte-read out of the client's own parser
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(`simpleexp 0x6fd240`, `getunopr 0x6fe0a0`, `getbinopr 0x6fe0c0`), all landing on 5.0's own
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`unexpected symbol` at `prefixexp 0x6fde40`:
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| hunk | why |
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|---|---|
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| `simpleexp`'s `case TK_DOTS` deleted: `...` is not an expression | the Ace2 corpus asks which interpreter it is on by compiling `return function(...) return ... end`; 170 `loadstring` sites in the corpus are that question, and 92 library files in 24 folders branch on the answer |
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| `getunopr`'s `case '#'` deleted: no length operator | the client's `getunopr` tests exactly two tokens (`-`, `not`) and its `OPR_NOUNOPR` is 2, a three-member enum; 5.0 asks a table with `table.getn` and a string with `string.len` |
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| `getbinopr`'s `case '%'` deleted: no modulo operator | the client's `getbinopr` switch is based at `'*'` (0x2A), so `%` (0x25) is below its range and reaches `OPR_NOBINOPR` = 14, a fifteen-member `BinOpr`; 5.0 spells it `math.mod` |
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The deletions are safe because nothing the reference runs uses those constructs: a comment- and
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string-stripping scan of the 1.12 FrameXML (177 files), GlueXML, Blizzard's own addons and the
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corpus finds zero sites of all three. No chunk of benilla's own Lua may use a construct the client's
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parser rejects.
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To verify the Lua sources against upstream at any time:
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```sh
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# 550.0.0 is the pinned version; adjust the path if cargo's registry hash differs.
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diff -r third_party/lua-src/lua-5.1.5 \
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~/.cargo/registry/src/*/lua-src-550.0.0/lua-5.1.5
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```
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That must print exactly the eight hunks in the tables above and nothing else.
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## The generic-for, in detail
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The `lvm.c` comment carries the three details that are the client's own, each byte-read there: the
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substitution test is a bare type-tag equality that never consults a metatable (a table carrying
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`__call` still gets `next`); the callee is the global `next`, read raw and fetched fresh at every loop
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entry (an addon assigning `next = myfn` changes every later generic-for in the session); and userdata
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is not substituted. The substitution happens in `OP_TFORPREP`, an opcode 5.1 deleted, so the top of
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`OP_TFORLOOP` is where 5.1 can host it.
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