macho: fix linking of dylibs and frameworks

Previously, I have incorrectly assumed that with two-level namespace
we only need to link in dylibs/frameworks that actually export symbols
which are undefined in the linked image. Turns out, regardless of
whether we link with two-level namespace (default on macOS) or a
flat namespace (more common on other platforms), we always need to
put the dylibs/frameworks as specified by the user from the linker
line into the final linked image.

src/link/MachO.zig

@@ -1013,7 +1013,12 @@ fn parseInputFiles(self: *MachO, files: []const []const u8, syslibroot: ?[]const
             .syslibroot = syslibroot,
         })) |dylibs| {
             defer self.base.allocator.free(dylibs);
+            const dylib_id = @intCast(u16, self.dylibs.items.len);
             try self.dylibs.appendSlice(self.base.allocator, dylibs);
+            // We always have to add the dylib that was on the linker line.
+            if (!self.referenced_dylibs.contains(dylib_id)) {
+                try self.referenced_dylibs.putNoClobber(self.base.allocator, dylib_id, {});
+            }
             continue;
         }
 
@@ -1028,7 +1033,12 @@ fn parseLibs(self: *MachO, libs: []const []const u8, syslibroot: ?[]const u8) !v
             .syslibroot = syslibroot,
         })) |dylibs| {
             defer self.base.allocator.free(dylibs);
+            const dylib_id = @intCast(u16, self.dylibs.items.len);
             try self.dylibs.appendSlice(self.base.allocator, dylibs);
+            // We always have to add the dylib that was on the linker line.
+            if (!self.referenced_dylibs.contains(dylib_id)) {
+                try self.referenced_dylibs.putNoClobber(self.base.allocator, dylib_id, {});
+            }
             continue;
         }
 

src/link/MachO/Dylib.zig

@@ -193,6 +193,8 @@ pub fn createAndParseFromPath(
     defer dylibs.deinit();
 
     try dylibs.append(dylib);
+    // TODO this should not be performed if the user specifies `-flat_namespace` flag.
+    // See ld64 manpages.
     try dylib.parseDependentLibs(allocator, arch, &dylibs, opts.syslibroot);
 
     return dylibs.toOwnedSlice();

test/standalone.zig

@@ -16,6 +16,7 @@ pub fn addCases(cases: *tests.StandaloneContext) void {
     cases.addBuildFile("test/standalone/link_interdependent_static_c_libs/build.zig", .{});
     cases.addBuildFile("test/standalone/link_static_lib_as_system_lib/build.zig", .{});
     cases.addBuildFile("test/standalone/link_common_symbols/build.zig", .{});
+    cases.addBuildFile("test/standalone/link_frameworks/build.zig", .{ .requires_macos_sdk = true });
     cases.addBuildFile("test/standalone/issue_339/build.zig", .{});
     cases.addBuildFile("test/standalone/issue_8550/build.zig", .{});
     cases.addBuildFile("test/standalone/issue_794/build.zig", .{});

test/standalone/link_frameworks/build.zig

@@ -0,0 +1,34 @@
+const std = @import("std");
+const Builder = std.build.Builder;
+const CrossTarget = std.zig.CrossTarget;
+
+fn isRunnableTarget(t: CrossTarget) bool {
+    // TODO I think we might be able to run this on Linux via Darling.
+    // Add a check for that here, and return true if Darling is available.
+    if (t.isNative() and t.getOsTag() == .macos)
+        return true
+    else
+        return false;
+}
+
+pub fn build(b: *Builder) void {
+    const mode = b.standardReleaseOptions();
+    const target = b.standardTargetOptions(.{});
+
+    const test_step = b.step("test", "Test the program");
+
+    const exe = b.addExecutable("test", null);
+    b.default_step.dependOn(&exe.step);
+    exe.addCSourceFile("main.c", &[0][]const u8{});
+    exe.setBuildMode(mode);
+    exe.setTarget(target);
+    exe.linkLibC();
+    // TODO when we figure out how to ship framework stubs for cross-compilation,
+    // populate paths to the sysroot here.
+    exe.linkFramework("Cocoa");
+
+    if (isRunnableTarget(target)) {
+        const run_cmd = exe.run();
+        test_step.dependOn(&run_cmd.step);
+    }
+}

test/standalone/link_frameworks/main.c

@@ -0,0 +1,7 @@
+#include <assert.h>
+#include <objc/runtime.h>
+
+int main() {
+  assert(objc_getClass("NSObject") > 0);
+  assert(objc_getClass("NSApplication") > 0);
+}