Switch to Diff Match Patch (diffz) (#982)

* Add tests, note about correctness issue

* Use diffz (DiffMatchPatch)

tests/tests.zig

@@ -5,6 +5,7 @@ comptime {
     _ = @import("utility/offsets.zig");
     _ = @import("utility/position_context.zig");
     _ = @import("utility/uri.zig");
+    _ = @import("utility/diff.zig");
 
     // TODO Lifecycle Messages
 

tests/utility/diff.zig

@@ -0,0 +1,30 @@
+const std = @import("std");
+const zls = @import("zls");
+
+const allocator = std.testing.allocator;
+
+fn gen(alloc: std.mem.Allocator, rand: std.rand.Random) ![]const u8 {
+    var buffer = try alloc.alloc(u8, rand.intRangeAtMost(usize, 16, 1024));
+    for (buffer) |*b| b.* = rand.intRangeAtMost(u8, 32, 126);
+    return buffer;
+}
+
+test "diff - random" {
+    var arena = std.heap.ArenaAllocator.init(allocator);
+    defer arena.deinit();
+
+    var rand = std.rand.DefaultPrng.init(0);
+
+    var index: usize = 0;
+
+    while (index < 100) : (index += 1) {
+        defer _ = arena.reset(.retain_capacity);
+
+        const pre = try gen(arena.allocator(), rand.random());
+        const post = try gen(arena.allocator(), rand.random());
+
+        var edits = try zls.diff.edits(arena.allocator(), pre, post, .@"utf-8");
+        const applied = try zls.diff.applyTextEdits(arena.allocator(), pre, edits.items, .@"utf-8");
+        try std.testing.expectEqualStrings(post, applied);
+    }
+}