Fixed serde content detection for serde >= 1.0.220 (#582)

* Fixed serde content detection for serde >= 1.0.220

* Add regression test for #581

* Use once_cell to cache the type ids

* Remove the arbitrary fuzzer

* Remove test relying on serde internals

Author: juntyr

.github/workflows/ci.yaml

@@ -2,14 +2,14 @@ name: CI
 on:
   push:
     branches:
-    - master
-    - 'v*.*'
+      - master
+      - "v*.*"
   pull_request:
     branches:
-    - master
-    - 'v*.*'
+      - master
+      - "v*.*"
   schedule:
-    - cron: '0 0 * * 0'
+    - cron: "0 0 * * 0"
 
 jobs:
   lock:
@@ -73,7 +73,11 @@ jobs:
           cargo update -p serde_bytes --precise 0.11.16
           cargo update -p indexmap --precise 2.5.0
           cargo update -p once_cell --precise 1.20.3
-        if: ${{ matrix.rust == '1.64.0' || matrix.rust == '1.81.0' }}
+          cargo update -p quote --precise 1.0.41
+          cargo update -p syn$(perl -ne 'm/syn (2\.\d+\.\d+)/ && print "\@$1\n"' Cargo.lock) --precise 2.0.106
+          cargo update -p typetag --precise 0.2.20
+          cargo update -p erased-serde --precise 0.4.8
+        if: ${{ matrix.rust == '1.64.0' }}
       - name: Check
         run: |
           cargo hack check --feature-powerset --no-dev-deps
@@ -108,7 +112,7 @@ jobs:
           components: clippy
           override: true
       - run: cd fuzz && cargo clippy --all -- -D warnings
-  
+
   rustfmt:
     name: "Format: stable"
     runs-on: ubuntu-latest

.github/workflows/cibench.yml

@@ -7,8 +7,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Unreleased
 
 ### Additions
+
 - Added `into_inner()` method to `ron::ser::Serializer` to retrieve the inner writer. ([#588](https://github.com/ron-rs/ron/pull/588))
 
+### Bug Fixes
+
+- Fixed untagged enum deserialisation for serde >= 1.0.220 with better serde content detection ([#582](https://github.com/ron-rs/ron/pull/582))
+
 ## [0.11.0] - 2025-08-27
 
 ### API Changes

CHANGELOG.md

@@ -39,6 +39,8 @@ serde = { version = "1.0.181", default-features = false, features = ["alloc"] }
 serde_derive = { version = "1.0.181", default-features = false }
 unicode-ident = { version = "1.0", default-features = false }
 unicode-segmentation = { version = "1.12.0", optional = true, default-features = false }
+typeid = { version = "1.0.1", default-features = false }
+once_cell = { version = "1.20", default-features = false, features = ["alloc", "race"] }
 
 [dev-dependencies]
 serde = { version = "1.0.181", default-features = false, features = ["std", "derive"] }

Cargo.toml

@@ -224,7 +224,7 @@ Please file a [new issue](https://github.com/ron-rs/ron/issues/new) if you come
 
 While RON guarantees roundtrips like Rust -> RON -> Rust for Rust types using non-`deserialize_any`-based implementations, RON does not yet make any guarantees about roundtrips through `ron::Value`. For instance, even when RON -> Rust works, RON -> `ron::Value` -> Rust, or RON -> `ron::Value` -> RON -> Rust may not work. We plan on improving `ron::Value` in an upcoming version of RON, though this work is partially blocked on [serde#1183](https://github.com/serde-rs/serde/issues/1183).
 
-[^serde-enum-hack]: Deserialising an internally, adjacently, or un-tagged enum requires detecting `serde`'s internal `serde::__private::de::content::Content` content type so that RON can describe the deserialised data structure in serde's internal JSON-like format. This detection only works for the automatically-derived [`Deserialize`](https://docs.rs/serde/latest/serde/de/trait.Deserialize.html) impls on enums. See [#451](https://github.com/ron-rs/ron/pull/451) for more details.
+[^serde-enum-hack]: Deserialising an internally, adjacently, or un-tagged enum requires detecting `serde`'s internal default buffer/content type so that RON can describe the deserialised data structure in serde's internal JSON-like format. A more robust implementation is blocked on [serde#1183](https://github.com/serde-rs/serde/issues/1183).
 
 [^serde-flatten-hack]: Deserialising a flattened struct from a map requires that the struct's [`Visitor::expecting`](https://docs.rs/serde/latest/serde/de/trait.Visitor.html#tymethod.expecting) implementation formats a string starting with `"struct "`. This is the case for automatically-derived [`Deserialize`](https://docs.rs/serde/latest/serde/de/trait.Deserialize.html) impls on structs. See [#455](https://github.com/ron-rs/ron/pull/455) for more details.
 

README.md

@@ -9,14 +9,8 @@ edition = "2018"
 cargo-fuzz = true
 
 [dependencies]
-arbitrary = { version = "1.0", default-features = false, features = ["derive"] }
 libfuzzer-sys = { version = "0.4", default-features = false, features = ["link_libfuzzer"] }
 ron = { path = "..", default-features = false, features = ["integer128", "std"] }
-serde = { version = "1.0", default-features = false, features = ["std", "derive"] }
-erased-serde = { version = "0.4", default-features = false, features = ["std"] }
-anyhow = { version = "1.0", default-features = false, features = ["std"] }
-criterion = { version = "0.5", default-features = false }
-serde_path_to_error = { version = "0.1", default-features = false }
 
 # Prevent this from interfering with workspaces
 [workspace]
@@ -27,14 +21,3 @@ name = "from_str"
 path = "fuzz_targets/from_str.rs"
 test = false
 doc = false
-
-[[bin]]
-name = "arbitrary"
-path = "fuzz_targets/arbitrary.rs"
-test = false
-doc = false
-
-[[bench]]
-name = "bench"
-path = "fuzz_targets/bench/main.rs"
-harness = false