Remove duplicate dylibs

This is a loader hard-error now to load the same library multiple
times since macOS 15.

Author: kubkon

src/Dylib.zig

@@ -658,6 +658,12 @@ pub fn isAlive(self: Dylib, macho_file: *MachO) bool {
     return self.referenced or self.needed;
 }
 
+pub fn markDead(self: *Dylib) void {
+    self.referenced = false;
+    self.needed = false;
+    self.explicit = false;
+}
+
 pub fn markReferenced(self: *Dylib, macho_file: *MachO) void {
     const tracy = trace(@src());
     defer tracy.end();
@@ -1011,6 +1017,22 @@ pub const Id = struct {
 
         return out;
     }
+
+    pub fn eql(id: Id, other: Id) bool {
+        return mem.eql(u8, id.name, other.name) and
+            id.timestamp == other.timestamp and
+            id.current_version == other.current_version and
+            id.compatibility_version == other.compatibility_version;
+    }
+
+    pub fn hash(id: Id) u64 {
+        var hasher = std.hash.Wyhash.init(0);
+        hasher.update(id.name);
+        hasher.update(mem.asBytes(&id.timestamp));
+        hasher.update(mem.asBytes(&id.current_version));
+        hasher.update(mem.asBytes(&id.compatibility_version));
+        return hasher.final();
+    }
 };
 
 const Export = struct {

src/MachO.zig

@@ -249,6 +249,7 @@ pub fn link(self: *MachO) !void {
     }
 
     try self.parseInputFiles();
+    try self.dedupDylibs(resolved_objects.items);
     try self.parseDependentDylibs(arena, lib_dirs.items, framework_dirs.items);
 
     if (!self.options.relocatable) {
@@ -832,6 +833,41 @@ fn isHoisted(self: *MachO, install_name: []const u8) bool {
     return false;
 }
 
+fn dedupDylibs(self: *MachO, resolved_objects: []const LinkObject) !void {
+    const tracy = trace(@src());
+    defer tracy.end();
+
+    var map = std.HashMap(Dylib.Id, void, struct {
+        pub fn hash(ctx: @This(), id: Dylib.Id) u64 {
+            _ = ctx;
+            return id.hash();
+        }
+
+        pub fn eql(ctx: @This(), id: Dylib.Id, other: Dylib.Id) bool {
+            _ = ctx;
+            return id.eql(other);
+        }
+    }, std.hash_map.default_max_load_percentage).init(self.allocator);
+    defer map.deinit();
+    try map.ensureTotalCapacity(@intCast(self.dylibs.items.len));
+
+    for (self.dylibs.items) |index| {
+        const dylib = self.getFile(index).dylib;
+        const cmd_object = resolved_objects[@intFromEnum(index)];
+
+        const gop = map.getOrPutAssumeCapacity(dylib.id.?);
+
+        if (!gop.found_existing) continue;
+        if (cmd_object.tag == .lib) {
+            self.warn("ignoring duplicate libraries: {}", .{cmd_object});
+        }
+
+        dylib.markDead();
+    }
+
+    try self.removeDylibs();
+}
+
 fn parseDependentDylibs(
     self: *MachO,
     arena: Allocator,
@@ -1036,6 +1072,10 @@ fn deadStripDylibs(self: *MachO) !void {
         self.getFile(index).dylib.markReferenced(self);
     }
 
+    try self.removeDylibs();
+}
+
+fn removeDylibs(self: *MachO) !void {
     var stripped = std.AutoHashMap(File.Index, void).init(self.allocator);
     defer stripped.deinit();
     try stripped.ensureTotalCapacity(@intCast(self.dylibs.items.len));

test/macho.zig

@@ -407,6 +407,7 @@ fn testDedupDylibs(b: *Build, opts: Options) *Step {
         "-install_name",
         "@rpath/liba.dylib",
         "-lSystem",
+        "-lSystem",
         "-lc",
     });