Issue #545 : yield across pcall or a Go call boundary raises the Lua 5.1 error

[eldologuzzo]

Fixes #545 .

Changes proposed in this pull request:

• A coroutine that yielded from a Lua function called by Go code (pcall, xpcall, a table.sort comparator, any Go function calling Lua) unwound the nested main loop of that Go call. The next resume then crashed with a nil pointer dereference.
• New LState.nCcalls: it counts the Go-to-Lua calls (callR) in progress on the thread, and PCall restores it when it recovers an error.
• When a Go function returns -1 (yield) inside a coroutine while a nested call is in progress, it now raises attempt to yield across metamethod/C-call boundary. The enclosing pcall catches it and the coroutine keeps running, which is the Lua 5.1 behavior discussed in pcall doesn't work in conjection with coroutines. #45.
• A yield at the top level of a coroutine is unchanged.
• Edited _state.go and _vm.go; state.go and vm.go are regenerated with make build.
• Tests in _glua-tests/coroutine.lua (yield inside pcall, inside a table.sort comparator, the coroutine continuing after the caught error, plain yields). On current master they fail.

🤖 Generated with Claude Code

[Copilot]

🟢 Approval recommended

The counter remains balanced across normal and protected-error paths, and the tests cover the reported crash and preserved yield behavior.

0 open findings

What changed in this PR

Prevents coroutine yields from crossing non-resumable Go call boundaries, matching Lua 5.1 behavior and avoiding resume crashes.

Changes:

• Tracks active Go-to-Lua calls and restores the counter after protected errors.
• Raises the Lua 5.1 boundary error for invalid yields.
• Adds regression coverage for pcall, table.sort, continuation, and normal yields.

File	Description
_state.go	Implements call-boundary tracking and recovery.
state.go	Regenerated state implementation.
_vm.go	Rejects invalid cross-boundary yields.
vm.go	Regenerated VM implementation.
value.go	Adds the per-thread call counter.
_glua-tests/​coroutine.lua	Adds coroutine regression tests.

🧠 Review effort: Balanced

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