Compilation: unconditionally close open file handles for writable dance

src/Compilation.zig

@@ -2295,10 +2295,16 @@ pub fn update(comp: *Compilation, main_progress_node: *std.Progress.Node) !void
         defer comp.gpa.free(o_sub_path);
 
         // Work around windows `AccessDenied` if any files within this directory are open
-        // by doing the makeExecutable/makeWritable dance.
+        // by closing and reopening the file handles.
         const need_writable_dance = builtin.os.tag == .windows and comp.bin_file.file != null;
         if (need_writable_dance) {
-            try comp.bin_file.makeExecutable();
+            // We cannot just call `makeExecutable` as it makes a false assumption that we have a
+            // file handle open only when linking an executable file. This used to be true when
+            // our linkers were incapable of emitting relocatables and static archive. Now that
+            // they are capable, we need to unconditionally close the file handle and re-open it
+            // in the follow up call to `makeWritable`.
+            comp.bin_file.file.?.close();
+            comp.bin_file.file = null;
         }
 
         try comp.bin_file.renameTmpIntoCache(comp.local_cache_directory, tmp_dir_sub_path, o_sub_path);

src/link/Elf.zig

@@ -943,7 +943,6 @@ pub fn flushModule(self: *Elf, comp: *Compilation, prog_node: *std.Progress.Node
 
     if (self.isObject() and self.zig_object_index == null) {
         // TODO this will become -r route I guess. For now, just copy the object file.
-        assert(self.base.file == null); // TODO uncomment once we implement -r
         const the_object_path = blk: {
             if (self.base.options.objects.len != 0) {
                 break :blk self.base.options.objects[0].path;