From 3de49cebd884d25ac18a15ccde3ec94d662cc17d Mon Sep 17 00:00:00 2001
From: AskSkivdal <mail@askskivdal.com>
Date: Fri, 31 Oct 2025 09:44:27 +0100
Subject: [PATCH] #65 Support untagged enums

---
 src/to_typescript/enums.rs                   | 61 +++++++++++++++++++-
 test/issue-65-untagged-enums/rust.rs         | 20 +++++++
 test/issue-65-untagged-enums/tsync.sh        |  8 +++
 test/issue-65-untagged-enums/typescript.d.ts | 16 +++++
 test/issue-65-untagged-enums/typescript.ts   | 16 +++++
 test/test_all.sh                             |  1 +
 6 files changed, 121 insertions(+), 1 deletion(-)
 create mode 100644 test/issue-65-untagged-enums/rust.rs
 create mode 100755 test/issue-65-untagged-enums/tsync.sh
 create mode 100644 test/issue-65-untagged-enums/typescript.d.ts
 create mode 100644 test/issue-65-untagged-enums/typescript.ts

diff --git a/src/to_typescript/enums.rs b/src/to_typescript/enums.rs
index 30e3f6c..3d72445 100644
--- a/src/to_typescript/enums.rs
+++ b/src/to_typescript/enums.rs
@@ -20,8 +20,12 @@ impl super::ToTypescript for syn::ItemEnum {
         let is_single = !self.variants.iter().any(|x| !x.fields.is_empty());
         state.write_comments(&comments, 0);
 
+        // Handle untagged enum if serde has the tag untagged
+        if utils::get_attribute_arg("serde", "untagged", &self.attrs).is_some() {
+            add_untagged_tagged_enum(self, state, casing, config.uses_type_interface);
+        }
         // always use output the internally_tagged representation if the tag is present
-        if let Some(tag_name) = utils::get_attribute_arg("serde", "tag", &self.attrs) {
+        else if let Some(tag_name) = utils::get_attribute_arg("serde", "tag", &self.attrs) {
             let content_name = utils::get_attribute_arg("serde", "content", &self.attrs);
             add_internally_tagged_enum(
                 tag_name,
@@ -398,3 +402,58 @@ fn add_externally_tagged_enum(
     }
     state.types.push_str(";\n");
 }
+
+fn add_untagged_tagged_enum(
+    exported_struct: syn::ItemEnum,
+    state: &mut BuildState,
+    casing: Option<Case>,
+    uses_type_interface: bool,
+) {
+    let export = if uses_type_interface { "" } else { "export " };
+    let generics = utils::extract_struct_generics(exported_struct.generics.clone());
+
+    // Write type name and generics
+    state.types.push_str(&format!(
+        "{export}type {interface_name}{generics} =",
+        interface_name = exported_struct.ident,
+        generics = utils::format_generics(&generics)
+    ));
+
+    // Loop over each variant of the enum
+    for variant in exported_struct.variants {
+        state.types.push('\n');
+        // Copy comments from rust
+        let comments = utils::get_comments(variant.attrs);
+        state.write_comments(&comments, 2);
+
+        // Unnamed fields:
+        // ```rs
+        // enum Data {
+        //     Value1(i32)
+        // }
+        // ```
+        if let syn::Fields::Unnamed(fields) = &variant.fields {
+            // add discriminant
+            state.types.push_str(&format!("  | "));
+            super::structs::process_tuple_fields(fields.clone(), state);
+            state.types.push_str("");
+        }
+        // Named fields:
+        // ```rs
+        // enum Data {
+        //     Value1 { v: i32 }
+        // }
+        // ```
+        else {
+            // add discriminant
+            state.types.push_str(&format!("  | {{\n"));
+
+            super::structs::process_fields(variant.fields, state, 6, casing, true);
+
+            state
+                .types
+                .push_str(&format!("{}}}", utils::build_indentation(4)));
+        }
+    }
+    state.types.push_str(";\n");
+}
diff --git a/test/issue-65-untagged-enums/rust.rs b/test/issue-65-untagged-enums/rust.rs
new file mode 100644
index 0000000..820ad72
--- /dev/null
+++ b/test/issue-65-untagged-enums/rust.rs
@@ -0,0 +1,20 @@
+/// test/rust.rs
+use tsync::tsync;
+
+#[derive(Serialize, Deserialize)]
+#[tsync]
+#[serde(untagged)]
+enum Message {
+    ValueOne(i32, i32),
+    Value2(i32),
+}
+
+#[derive(Serialize, Deserialize)]
+#[tsync]
+#[serde(untagged)]
+enum Message2<V, G> {
+    ValueOne { a: V, b: G },
+    Value2 { c: V },
+    Value3(G),
+    Value3(Vec<G>),
+}
diff --git a/test/issue-65-untagged-enums/tsync.sh b/test/issue-65-untagged-enums/tsync.sh
new file mode 100755
index 0000000..1764bd6
--- /dev/null
+++ b/test/issue-65-untagged-enums/tsync.sh
@@ -0,0 +1,8 @@
+#!/bin/bash
+
+SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )"
+
+cd $SCRIPT_DIR
+
+cargo run -- -i rust.rs -o typescript.d.ts
+cargo run -- -i rust.rs -o typescript.ts
\ No newline at end of file
diff --git a/test/issue-65-untagged-enums/typescript.d.ts b/test/issue-65-untagged-enums/typescript.d.ts
new file mode 100644
index 0000000..08b1f76
--- /dev/null
+++ b/test/issue-65-untagged-enums/typescript.d.ts
@@ -0,0 +1,16 @@
+/* This file is generated and managed by tsync */
+
+type Message =
+  | [ number, number ]
+  | number;
+
+type Message2<V, G> =
+  | {
+      a: V;
+      b: G;
+    }
+  | {
+      c: V;
+    }
+  | G
+  | Array<G>;
diff --git a/test/issue-65-untagged-enums/typescript.ts b/test/issue-65-untagged-enums/typescript.ts
new file mode 100644
index 0000000..f2b6155
--- /dev/null
+++ b/test/issue-65-untagged-enums/typescript.ts
@@ -0,0 +1,16 @@
+/* This file is generated and managed by tsync */
+
+export type Message =
+  | [ number, number ]
+  | number;
+
+export type Message2<V, G> =
+  | {
+      a: V;
+      b: G;
+    }
+  | {
+      c: V;
+    }
+  | G
+  | Array<G>;
diff --git a/test/test_all.sh b/test/test_all.sh
index 8235449..fa9feb8 100755
--- a/test/test_all.sh
+++ b/test/test_all.sh
@@ -17,4 +17,5 @@ cd $SCRIPT_DIR
 ./issue-43/tsync.sh
 ./issue-55/tsync.sh
 ./issue-58/tsync.sh
+./issue-65-untagged-enums/tsync.sh
 ./raw_identifiers/tsync.sh