lib-vt: setup a default allocator if null

1 files changed, 16 insertions, 0 deletions

diff --git a/src/lib/allocator.zig b/src/lib/allocator.zig
index ef296f23d..de1453dbe 100644
--- a/src/lib/allocator.zig
+++ b/src/lib/allocator.zig
@@ -13,6 +13,22 @@ pub const VTable = extern struct {
     free: *const fn (*anyopaque, memory: [*]u8, memory_len: usize, alignment: u8, ret_addr: usize) callconv(.c) void,
 };
 
+/// Returns an allocator to use for the given possibly-null C allocator,
+/// ensuring some allocator is always returned.
+pub fn default(c_alloc_: ?*const Allocator) std.mem.Allocator {
+    // If we're given an allocator, use it.
+    if (c_alloc_) |c_alloc| return c_alloc.zig();
+
+    // If we have libc, use that. We prefer libc if we have it because
+    // its generally fast but also lets the embedder easily override
+    // malloc/free with custom allocators like mimalloc or something.
+    if (comptime builtin.link_libc) return std.heap.c_allocator;
+
+    // No libc, use the preferred allocator for releases which is the
+    // Zig SMP allocator.
+    return std.heap.smp_allocator;
+}
+
 /// The Allocator interface for custom memory allocation strategies
 /// within C libghostty APIs.
 ///