From 57b360a570bfa289aa6f8dd02357c717a0bfe2d2 Mon Sep 17 00:00:00 2001
From: Altagos <jakob@altagos.dev>
Date: Sun, 25 Jan 2026 11:39:59 +0000
Subject: [PATCH] pretty unions

---
 pretty.zig | 32 ++++++++++++++++++++++++++++++--
 example/main.zig | 15 ++++++++++++++-
 2 file(s) changed, 44 insertion(s)(+), 3 deletion(s)(-)

diff --git a/pretty.zig b/pretty.zig
--- a/pretty.zig
+++ b/pretty.zig
@@ -30,6 +30,7 @@
     inline_slice: bool = false,
 
     inline_structs: bool = false,
+    highlight_union_tag: bool = true,
 
     show_type_names: bool = true,
     always_show_type_names: bool = false,
@@ -139,7 +140,7 @@
     }
 
     pub inline fn write(this: *const Runtime, text: []const u8) error{WriteFailed}!void {
-        return this.out.writeAll(text);
+        _ = try this.out.write(text);
     }
 
     pub inline fn setColor(
@@ -188,7 +189,7 @@
     const info = @typeInfo(T);
 
     if (!opts.skip_type_name)
-        try printType(T, ctx, run);
+        try printType(T, ctx, run, value);
 
     return switch (info) {
         .bool => formatBool(ctx, run, value),
@@ -208,6 +209,7 @@
 
         .optional => |opt| formatOptional(opt.child, ctx, run, value),
         .@"struct" => |st| formatStruct(T, ctx, st, run, value),
+        .@"union" => formatUnion(T, ctx, run, value),
 
         .error_set => formatErrorSet(ctx, run, value),
         .error_union => formatErrorUnion(ctx, run, value),
@@ -240,6 +242,7 @@
     comptime T: type,
     comptime ctx: Context,
     run: *Runtime,
+    value: T,
 ) error{WriteFailed}!void {
     const active_type = comptime std.meta.activeTag(@typeInfo(T));
     const excluded = comptime switch (active_type) {
@@ -252,6 +255,20 @@
 
         if (ctx.options.show_type_names) {
             try run.write(@typeName(T));
+
+            if (active_type == .@"union") {
+                if (ctx.options.highlight_union_tag) {
+                    run.resetColor();
+                    run.setColor(ctx, .field);
+                }
+
+                try run.print("{}", .{std.meta.activeTag(value)});
+
+                if (ctx.options.highlight_union_tag) {
+                    run.resetColor();
+                    run.setColor(ctx, .dim);
+                }
+            }
         }
         try run.write(ctx.options.theme.type_value_sep);
 
@@ -354,6 +371,17 @@
         run.setColor(ctx, .dim);
         try run.write(" }");
         run.resetColor();
+    }
+}
+
+inline fn formatUnion(
+    comptime T: type,
+    comptime ctx: Context,
+    run: *Runtime,
+    value: T,
+) !void {
+    switch (value) {
+        inline else => |val| try innerFmt(@TypeOf(val), ctx, run, val, .{ .skip_type_name = true }),
     }
 }
 
diff --git a/example/main.zig b/example/main.zig
--- a/example/main.zig
+++ b/example/main.zig
@@ -89,6 +89,13 @@
 const ErrorSet = error{ OutOfMemory, WriteFailed };
 const Result = ErrorSet!Hello;
 
+const HelloResult = union(ResultType) {
+    const ResultType = enum { ok, err };
+
+    ok: Hello,
+    err: ErrorSet,
+};
+
 pub fn main(init: std.process.Init) !void {
     print("Pretty type - {f}\n", .{pretty(Hello)});
     print("Pretty null - {f}\n", .{pretty(null)});
@@ -154,6 +161,11 @@
     );
     print("Pretty nested struct - {f}\n", .{pretty(nested)});
 
+    const simple_union = HelloResult{ .ok = .world };
+
+    print("\nUnions\n", .{});
+    print("Pretty simple union - {f}\n", .{pretty(simple_union)});
+
     print("\nArrays\n", .{});
     print("Pretty array of floats - {f}\n", .{pretty([_]f32{ 0.1, 0.2, 0.3 })});
     print(
@@ -213,5 +225,6 @@
     defer parsed.deinit();
 
     print("\nJson\n", .{});
-    print("{}", .{parsed.value});
+    print("Data - {f}\n", pretty(pretty(employees)));
+    print("{f}\n", .{pretty(parsed.value)});
 }

--
tangled.sh