macho: read-in committed ZigObject to memory from file

src/link/MachO/ZigObject.zig

@@ -1,3 +1,4 @@
+data: std.ArrayListUnmanaged(u8) = .{},
 /// Externally owned memory.
 path: []const u8,
 index: File.Index,
@@ -57,6 +58,7 @@ pub fn init(self: *ZigObject, macho_file: *MachO) !void {
 }
 
 pub fn deinit(self: *ZigObject, allocator: Allocator) void {
+    self.data.deinit(allocator);
     self.symtab.deinit(allocator);
     self.strtab.deinit(allocator);
     self.symbols.deinit(allocator);
@@ -279,6 +281,22 @@ pub fn checkDuplicates(self: *ZigObject, dupes: anytype, macho_file: *MachO) !vo
     }
 }
 
+/// This is just a temporary helper function that allows us to re-read what we wrote to file into a buffer.
+/// We need this so that we can write to an archive.
+/// TODO implement writing ZigObject data directly to a buffer instead.
+pub fn readFileContents(self: *ZigObject, macho_file: *MachO) !void {
+    const gpa = macho_file.base.comp.gpa;
+    var end_pos: u64 = 0;
+    for (macho_file.segments.items) |seg| {
+        end_pos = @max(end_pos, seg.fileoff + seg.filesize);
+    }
+    const size = std.math.cast(usize, end_pos) orelse return error.Overflow;
+    try self.data.resize(gpa, size);
+
+    const amt = try macho_file.base.file.?.preadAll(self.data.items, 0);
+    if (amt != size) return error.InputOutput;
+}
+
 pub fn scanRelocs(self: *ZigObject, macho_file: *MachO) !void {
     for (self.atoms.items) |atom_index| {
         const atom = macho_file.getAtom(atom_index) orelse continue;

src/link/MachO/relocatable.zig

@@ -144,6 +144,10 @@ pub fn flushStaticLib(macho_file: *MachO, comp: *Compilation, module_obj_path: ?
 
         const ncmds, const sizeofcmds = try writeLoadCommands(macho_file);
         try writeHeader(macho_file, ncmds, sizeofcmds);
+
+        // TODO we can avoid reading in the file contents we just wrote if we give the linker
+        // ability to write directly to a buffer.
+        try zo.readFileContents(macho_file);
     }
 
     var err = try macho_file.addErrorWithNotes(0);