link same day twice

src/test.zig

@@ -10,6 +10,7 @@ const Allocator = std.mem.Allocator;
 const LocalDate = date.LocalDate;
 const ChainDb = main.ChainDb;
 const LinkDb = main.LinkDb;
+const Link = main.Link;
 
 var allocator = std.heap.c_allocator;
 const print_output = false;
@@ -50,6 +51,11 @@ const TmpDb = struct {
         }
     }
 
+    fn unloadFiles(self: *Self) void {
+        if (self.files) |*fs| fs.close();
+        self.files = null;
+    }
+
     fn deinit(self: *Self) void {
         if (self.files) |*fs| fs.close();
         self.tmpdir.cleanup();
@@ -103,6 +109,44 @@ test "basic" {
     try expectEqual(@as(i64, 1704063600), link_db.links.items[0].timestamp);
 }
 
+test "linking same day twice" {
+    var db = try TmpDb.init();
+    defer db.deinit();
+
+    const commands = [_][]const u8{
+        "",
+        "add Foo daily",
+        "link 1 20240101",
+    };
+
+    for (commands) |arg| {
+        try runCommand(db.path, arg);
+    }
+
+    {
+        defer db.unloadFiles();
+
+        var link_db = db.linkDb();
+        try link_db.materialize(1);
+
+        const meta = link_db.meta;
+        try expectEqual(meta.len, 1);
+
+        try expectEqualSlices(Link, link_db.links.items, &.{ Link{ .chain_id = 0, .timestamp = 1704063600, .tags = 0}});
+    }
+
+    try runCommand(db.path, "link 1 20240101");
+    {
+        var link_db = db.linkDb();
+        try link_db.materialize(1);
+
+        const meta = link_db.meta;
+        try expectEqual(meta.len, 1);
+
+        try expectEqualSlices(Link, link_db.links.items, &.{ Link{ .chain_id = 0, .timestamp = 1704063600, .tags = 0}});
+    }
+}
+
 test "parse date" {
     try testDateParse(try LocalDate.init(2023, 1, 1), "20230101");
 }