Add too short sliders check and tests

osu.Game.Rulesets.Osu/Edit/Checks/CheckTooShortSliders.cs

@@ -0,0 +1,48 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Collections.Generic;
+using osu.Game.Beatmaps;
+using osu.Game.Rulesets.Edit;
+using osu.Game.Rulesets.Edit.Checks.Components;
+using osu.Game.Rulesets.Osu.Objects;
+
+namespace osu.Game.Rulesets.Osu.Edit.Checks
+{
+    public class CheckTooShortSliders : ICheck
+    {
+        /// <summary>
+        /// The shortest acceptable duration between the head and tail of the slider (so ignoring repeats).
+        /// </summary>
+        private const double span_duration_threshold = 125; // 240 BPM 1/2
+
+        public CheckMetadata Metadata { get; } = new CheckMetadata(CheckCategory.Spread, "Too short sliders");
+
+        public IEnumerable<IssueTemplate> PossibleTemplates => new IssueTemplate[]
+        {
+            new IssueTemplateTooShort(this)
+        };
+
+        public IEnumerable<Issue> Run(BeatmapVerifierContext context)
+        {
+            if (context.InterpretedDifficulty > DifficultyRating.Easy)
+                yield break;
+
+            foreach (var hitObject in context.Beatmap.HitObjects)
+            {
+                if (hitObject is Slider slider && slider.SpanDuration < span_duration_threshold)
+                    yield return new IssueTemplateTooShort(this).Create(slider);
+            }
+        }
+
+        public class IssueTemplateTooShort : IssueTemplate
+        {
+            public IssueTemplateTooShort(ICheck check)
+                : base(check, IssueType.Problem, "This slider is too short ({0:0} ms), expected at least {1:0} ms.")
+            {
+            }
+
+            public Issue Create(Slider slider) => new Issue(slider, this, slider.SpanDuration, span_duration_threshold);
+        }
+    }
+}