Feature: tests for the skipping seq access

tests/regression/issue_1263.rs

@@ -0,0 +1,81 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(tag = "type", seq_form=false)]
+enum ParentChildNoSeq {
+    Title,
+    #[serde(untagged)]
+    SubStructure(ChildNoSeq),
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(tag = "type", seq_form=false)]
+enum ParentNoSeq {
+    Title,
+    #[serde(untagged)]
+    SubStructure(Child),
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(tag = "type")]
+enum Parent {
+    Title,
+    #[serde(untagged)]
+    SubStructure(Child),
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(tag = "type", seq_form=true)]
+enum ParentSeq {
+    Title,
+    #[serde(untagged)]
+    SubStructure(Child),
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(tag = "subtype", seq_form=false)]
+enum ChildNoSeq {
+    Topic, Sidebar
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(tag = "subtype")]
+enum Child {
+    Topic, Sidebar
+}
+
+#[test]
+fn test() {
+    // Using seq=false on every level will cause it to fail
+    let v  = serde_json::from_str::<ParentChildNoSeq>("[0]");
+    assert!(v.is_err());
+
+    // Using seq=false will cause it to fail, but if the child is not seq=true, the  child will succeed
+    let v  = serde_json::from_str::<ParentNoSeq>("[0]");
+    assert!(matches!(v, Ok(ParentNoSeq::SubStructure(Child::Topic))));
+
+    // Using default beahvior will succeed
+    let v  = serde_json::from_str::<Parent>("[0]");
+    assert!(v.is_ok());
+
+    // Using seq=true beahvior will succeed
+    let v  = serde_json::from_str::<ParentSeq>("[0]");
+    assert!(v.is_ok());
+
+    // As in the docs:
+    // There is no explicit tag identifying which variant the data contains. Serde will try to
+    // match the data against each variant in order and the first one that deserializes
+    // successfully is the one returned.
+    let v = serde_json::from_str::<Parent>("[\"Topic\"]");
+    assert!(v.is_ok());
+    let v = serde_json::from_str::<Child>("[\"Topic\"]");
+    assert!(v.is_ok());
+
+    // With seq=false it should fail
+    let v = serde_json::from_str::<ChildNoSeq>("[\"Topic\"]");
+    assert!(v.is_err());
+    let v = serde_json::from_str::<ParentNoSeq>("[\"Topic\"]");
+    assert!(v.is_ok());
+    let v = serde_json::from_str::<ParentChildNoSeq>("[\"Topic\"]");
+    assert!(v.is_err());
+}