Fix JSON deserialization of abci::ResponseInfo (informalsystems#1131)

* Fix JSON deserialization of abci::ResponseInfo

The fields are annotated with json:"omitempty" in the Go source,
so give them default values for Deserialize. The /abci_info endpoint
is known to omit the app_version field in some recent revisions of Gaia.

* Changelog entry for informalsystems#1131

* Annotate last_block_add_hash with serde(default)

The only field of abci::ResponseInfo where it remained missing,
 to match the json:"omitempty" flag in Go.

* rpc: Drop "std" feature from serde_json dependency

* Revert "rpc: Drop "std" feature from serde_json dependency"

This reverts commit 11396ba.

.changelog/unreleased/bug-fixes/1132-allow-omitted-fields-in-abci_info.md

@@ -0,0 +1,4 @@
+- `[tools/proto-compiler]` Annotate serde to fall back to `Default` for the
+  omitted fields when deserializing `tendermint_proto::abci::ResponseInfo` struct,
+  also providing deserialization for the response at the `/abci_info` RPC endpoint.
+  ([#1132](https://github.com/informalsystems/tendermint-rs/issues/1132))

proto/src/prost/tendermint.abci.rs

@@ -216,17 +216,20 @@ pub struct ResponseFlush {
 #[derive(Clone, PartialEq, ::prost::Message)]
 pub struct ResponseInfo {
     #[prost(string, tag="1")]
+    #[serde(default)]
     pub data: ::prost::alloc::string::String,
     /// this is the software version of the application. TODO: remove?
     #[prost(string, tag="2")]
+    #[serde(default)]
     pub version: ::prost::alloc::string::String,
     #[prost(uint64, tag="3")]
-    #[serde(with = "crate::serializers::from_str")]
+    #[serde(with = "crate::serializers::from_str", default)]
     pub app_version: u64,
     #[prost(int64, tag="4")]
-    #[serde(with = "crate::serializers::from_str")]
+    #[serde(with = "crate::serializers::from_str", default)]
     pub last_block_height: i64,
     #[prost(bytes="bytes", tag="5")]
+    #[serde(default)]
     #[serde(skip_serializing_if = "bytes::Bytes::is_empty")]
     pub last_block_app_hash: ::prost::bytes::Bytes,
 }

tools/proto-compiler/src/constants.rs

@@ -14,6 +14,7 @@ const SERIALIZED: &str = r#"#[derive(::serde::Deserialize, ::serde::Serialize)]"
 const TYPE_TAG: &str = r#"#[serde(tag = "type", content = "value")]"#;
 
 /// Predefined custom attributes for field annotations
+const DEFAULT: &str = r#"#[serde(default)]"#;
 const QUOTED: &str = r#"#[serde(with = "crate::serializers::from_str")]"#;
 const QUOTED_WITH_DEFAULT: &str = r#"#[serde(with = "crate::serializers::from_str", default)]"#;
 const HEXSTRING: &str = r#"#[serde(with = "crate::serializers::bytes::hexstring")]"#;
@@ -85,14 +86,23 @@ pub static CUSTOM_FIELD_ATTRIBUTES: &[(&str, &str)] = &[
         ".tendermint.types.EvidenceParams.max_bytes",
         QUOTED_WITH_DEFAULT,
     ),
-    (".tendermint.abci.ResponseInfo.last_block_height", QUOTED),
     (".tendermint.version.Consensus.block", QUOTED),
     (".tendermint.version.Consensus.app", QUOTED_WITH_DEFAULT),
+    (".tendermint.abci.ResponseInfo.data", DEFAULT),
+    (".tendermint.abci.ResponseInfo.version", DEFAULT),
+    (
+        ".tendermint.abci.ResponseInfo.app_version",
+        QUOTED_WITH_DEFAULT,
+    ),
+    (
+        ".tendermint.abci.ResponseInfo.last_block_height",
+        QUOTED_WITH_DEFAULT,
+    ),
+    (".tendermint.abci.ResponseInfo.last_block_app_hash", DEFAULT),
     (
         ".tendermint.abci.ResponseInfo.last_block_app_hash",
         BYTES_SKIP_IF_EMPTY,
     ),
-    (".tendermint.abci.ResponseInfo.app_version", QUOTED),
     (".tendermint.types.BlockID.hash", HEXSTRING),
     (".tendermint.types.BlockID.part_set_header", ALIAS_PARTS),
     (