add std.zip and support zip files in build.zig.zon

fixes ziglang#17408

Improved by helpful reviews from Josh Wolfe and Auguste Rame and Andrew
Kelley.

Co-authored-by: Joel Gustafson <joelg@mit.edu>

lib/std/io.zig

@@ -344,6 +344,10 @@ pub fn GenericWriter(
             return @errorCast(self.any().writeStruct(value));
         }
 
+        pub inline fn writeStructEndian(self: Self, value: anytype, endian: std.builtin.Endian) Error!void {
+            return @errorCast(self.any().writeStructEndian(value, endian));
+        }
+
         pub inline fn any(self: *const Self) AnyWriter {
             return .{
                 .context = @ptrCast(&self.context),

lib/std/io/Writer.zig

@@ -1,6 +1,7 @@
 const std = @import("../std.zig");
 const assert = std.debug.assert;
 const mem = std.mem;
+const native_endian = @import("builtin").target.cpu.arch.endian();
 
 context: *const anyopaque,
 writeFn: *const fn (context: *const anyopaque, bytes: []const u8) anyerror!usize,
@@ -59,6 +60,17 @@ pub fn writeStruct(self: Self, value: anytype) anyerror!void {
     return self.writeAll(mem.asBytes(&value));
 }
 
+pub fn writeStructEndian(self: Self, value: anytype, endian: std.builtin.Endian) anyerror!void {
+    // TODO: make sure this value is not a reference type
+    if (native_endian == endian) {
+        return self.writeStruct(value);
+    } else {
+        var copy = value;
+        mem.byteSwapAllFields(@TypeOf(value), &copy);
+        return self.writeStruct(copy);
+    }
+}
+
 pub fn writeFile(self: Self, file: std.fs.File) anyerror!void {
     // TODO: figure out how to adjust std lib abstractions so that this ends up
     // doing sendfile or maybe even copy_file_range under the right conditions.

lib/std/mem.zig

@@ -2008,7 +2008,12 @@ pub fn byteSwapAllFields(comptime S: type, ptr: *S) void {
         .Struct => {
             inline for (std.meta.fields(S)) |f| {
                 switch (@typeInfo(f.type)) {
-                    .Struct, .Array => byteSwapAllFields(f.type, &@field(ptr, f.name)),
+                    .Struct => |struct_info| if (struct_info.backing_integer) |Int| {
+                        @field(ptr, f.name) = @bitCast(@byteSwap(@as(Int, @bitCast(@field(ptr, f.name)))));
+                    } else {
+                        byteSwapAllFields(f.type, &@field(ptr, f.name));
+                    },
+                    .Array => byteSwapAllFields(f.type, &@field(ptr, f.name)),
                     .Enum => {
                         @field(ptr, f.name) = @enumFromInt(@byteSwap(@intFromEnum(@field(ptr, f.name))));
                     },

lib/std/std.zig

@@ -104,6 +104,7 @@ pub const unicode = @import("unicode.zig");
 pub const valgrind = @import("valgrind.zig");
 pub const wasm = @import("wasm.zig");
 pub const zig = @import("zig.zig");
+pub const zip = @import("zip.zig");
 pub const start = @import("start.zig");
 
 const root = @import("root");