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https://github.com/ghostty-org/ghostty.git
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67db6b8960
## What
On Windows, calling `free()` on memory allocated by libghostty crashes
because Zig and MSVC use separate heaps.
This adds `ghostty_free()` so consumers can free library-allocated
memory safely on all platforms.
## Why
When Zig builds a DLL on Windows with `link_libc = true`, it does not
link the Windows C runtime (`ucrtbase.dll`). Instead it uses its own
libc built on top of `KERNEL32.dll`. So `builtin.link_libc` is true and
`c_allocator` is selected, but Zig's `malloc` and MSVC's `malloc` are
different implementations with different heaps. 💥
On Linux/macOS this is not a problem because Zig links the system libc
and everyone shares the same heap. On Windows, `free(buf)` from MSVC
tries to free memory from Zig's heap and you get a debug assertion
failure or undefined behavior.
The `format_alloc` docs said "the buffer can be freed with `free()`" but
that is only true when the library and consumer share the same C
runtime, which is not the case on Windows.
## How
- Add `ghostty_free(allocator, ptr, len)` that frees through the same
allocator that did the allocation
- Update `format_alloc` docs to point to `ghostty_free()` instead of
`free()`
- Update all 3 examples to use `ghostty_free(NULL, buf, len)`
The signature takes an allocator because raw buffers (unlike objects
like terminals or formatters) do not store their allocator internally.
The caller already has all three values: the allocator they passed, the
pointer, and the length they got back.
I went back and forth on the naming. Other options I considered:
`ghostty_alloc_free(allocator, ptr, len)` or returning a `GhosttyBuffer`
wrapper with its own `_free`. Happy to change the naming if there is a
preference.
No impact on Linux/macOS. `ghostty_free()` works correctly there too, it
just happens to call the same `free()` the consumer would have called
anyway.
## Verified
- `zig build test-lib-vt` passes on Windows, macOS arm64, Linux x86_64
(exit 0)
- `zig build test` passes on Windows (2575/2619 passed, 1 pre-existing
font sprite failure) and macOS (exit 0)
- cmake shared example builds, links, and runs correctly on Windows with
`ghostty_free()` (no more heap crash)
## What I Learnt
- What I wrote in Why
- Zig allocators require the length to free (no hidden metadata headers
like C's malloc). This is a deliberate design choice for explicit
control.
- The standard pattern for C libraries on Windows is "whoever allocates,
frees" (like `curl_free()`, `SDL_free()`). This avoids cross-runtime
heap issues entirely.