different behaviours when using callconv(.c) function #25452
Description
Zig Version
0.15.1
Steps to Reproduce and Observed Behavior
Very simple to reproduce:
const std = @import("std");
pub const Vec3 = extern struct { x: f32 = 0, y: f32 = 0, z: f32 = 0 };
pub fn vec3(x: f32, y: f32, z: f32) Vec3 {
return Vec3{ .x = x, .y = y, .z = z };
}
pub fn vec3add(arg_v1: Vec3, arg_v2: Vec3) Vec3 {
return Vec3{ .x = arg_v1.x + arg_v2.x, .y = arg_v1.y + arg_v2.y, .z = arg_v1.z + arg_v2.z };
}
pub fn vec3addConvC(arg_v1: Vec3, arg_v2: Vec3) callconv(.c) Vec3 {
return Vec3{ .x = arg_v1.x + arg_v2.x, .y = arg_v1.y + arg_v2.y, .z = arg_v1.z + arg_v2.z };
}
pub fn main() !void {
var position = vec3(5, 5, 0);
var target = vec3(5, 5, 5); //this doenst happen if target is const
target = vec3(5, 5, 5);
std.debug.print("expected {any}\n", .{target}); // vec3{ 5,5,5 }
position = vec3addConvC(vec3(5, 5, 0), target);
std.debug.print("actual {any}\n", .{target}); // vec3{ 0,5,5 }
}
If we use vec3add instead of vec3addConvC, the issue doesn't happen.
If we initialize the position after the target, the issue also doens't happen.
Expected Behavior
It is expected that the target doesn't change after adding it through the vec3addConvC. The expected value is to remain {5,5,5}, but we get {0,5,5} instead.