Fix: Skip deserialization of unrelated fields with overlapping name

src/cargo/util/context/de.rs

@@ -265,7 +265,15 @@ impl<'gctx> ConfigMapAccess<'gctx> {
             let mut field_key = de.key.clone();
             field_key.push(field);
             for env_key in de.gctx.env_keys() {
-                if env_key.starts_with(field_key.as_env_key()) {
+                let Some(nested_field) = env_key.strip_prefix(field_key.as_env_key()) else {
+                    continue;
+                };
+                // This distinguishes fields that share the same prefix.
+                // For example, when env_key is UNSTABLE_GITOXIDE_FETCH
+                // and field_key is UNSTABLE_GIT, the field shouldn't be
+                // added because `unstable.gitoxide.fetch` doesn't
+                // belong to `unstable.git` struct.
+                if nested_field.is_empty() || nested_field.starts_with('_') {
                     fields.insert(KeyKind::Normal(field.to_string()));
                 }
             }

tests/testsuite/config.rs

@@ -1454,7 +1454,6 @@ fn struct_with_overlapping_inner_struct_and_defaults() {
     // If, in the future, we can handle this more correctly, feel free to delete
     // this case.
     #[derive(Deserialize, Default)]
-    #[serde(default)]
     struct PrefixContainer {
         inn: bool,
         inner: Inner,
@@ -1466,7 +1465,7 @@ fn struct_with_overlapping_inner_struct_and_defaults() {
         .get::<PrefixContainer>("prefixcontainer")
         .err()
         .unwrap();
-    assert!(format!("{}", err).contains("missing config key `prefixcontainer.inn`"));
+    assert!(format!("{}", err).contains("missing field `inn`"));
     let gctx = GlobalContextBuilder::new()
         .env("CARGO_PREFIXCONTAINER_INNER_VALUE", "12")
         .env("CARGO_PREFIXCONTAINER_INN", "true")
@@ -1475,6 +1474,22 @@ fn struct_with_overlapping_inner_struct_and_defaults() {
     assert_eq!(f.inner.value, 12);
     assert_eq!(f.inn, true);
 
+    // Use default attribute of serde, then we can skip setting the inn field
+    #[derive(Deserialize, Default)]
+    #[serde(default)]
+    struct PrefixContainerFieldDefault {
+        inn: bool,
+        inner: Inner,
+    }
+    let gctx = GlobalContextBuilder::new()
+        .env("CARGO_PREFIXCONTAINER_INNER_VALUE", "12")
+        .build();
+    let f = gctx
+        .get::<PrefixContainerFieldDefault>("prefixcontainer")
+        .unwrap();
+    assert_eq!(f.inner.value, 12);
+    assert_eq!(f.inn, false);
+
     // Containing struct where the inner value's field is a prefix of another
     //
     // This is a limitation of mapping environment variables on to a hierarchy.