From a2f1209d39dd42c812e515369ed21e39430048fb Mon Sep 17 00:00:00 2001
From: Eugene Blikh <bigbes@gmail.com>
Date: Sat, 16 May 2026 00:22:27 +0300
Subject: [PATCH] json: drop unrecognized enum string names per proto3 spec

decode_enum returned the raw input string for unknown enum names,
which then propagated through the codec and errored at encode time
with "unknown enum value '...'". For repeated and map fields the
spec requires *dropping* the element (not substituting 0), so the
encoded output should be shorter than the input.

decode_enum now returns nil for unrecognized names. The optional /
repeated / map call sites in decode_message skip nil values: optional
leaves the field unset (encoded as default), repeated compacts the
array, map omits the entry. Numeric and known-name inputs are
unchanged.

Drops 5 entries from test/conformance/known_failures.txt:
IgnoreUnknownEnumStringValueIn{Optional,Repeated,RepeatedPart,
MapPart,MapValue}.
---
 runtime/pb/json.lua                 | 19 +++++++++++++++----
 test/conformance/known_failures.txt |  5 -----
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/runtime/pb/json.lua b/runtime/pb/json.lua
index 456266999c60d54f08baf1dc30fdaa907074184c..ca0931b8167de8da2a18ed4946bd301dd20f668e 100644
--- a/runtime/pb/json.lua
+++ b/runtime/pb/json.lua
@@ -364,7 +364,10 @@ local function decode_enum(enum_desc, v)
         local n = enum_desc.by_name[v]
         if n ~= nil then return n end
     end
-    return tonumber(v) or v
+    -- proto3 JSON: unrecognized integer enum values pass through; unrecognized
+    -- string names yield nil so the caller can drop the element (repeated/map)
+    -- or fall back to the field default (singular).
+    return tonumber(v)
 end
 
 local function decode_field_value(field, v)
@@ -518,15 +521,23 @@ decode_message = function(desc, v)
             if f.kind == 'map' then
                 local m = {}
                 for mk, mv in pairs(jv) do
-                    m[decode_map_key(f.key, mk)] = decode_field_value(f.value, mv)
+                    local dv = decode_field_value(f.value, mv)
+                    if dv ~= nil then
+                        m[decode_map_key(f.key, mk)] = dv
+                    end
                 end
                 out[f.name] = m
             elseif f.repeated then
                 local arr = {}
-                for i = 1, #jv do arr[i] = decode_field_value(f, jv[i]) end
+                local n = 0
+                for i = 1, #jv do
+                    local dv = decode_field_value(f, jv[i])
+                    if dv ~= nil then n = n + 1; arr[n] = dv end
+                end
                 out[f.name] = arr
             else
-                out[f.name] = decode_field_value(f, jv)
+                local dv = decode_field_value(f, jv)
+                if dv ~= nil then out[f.name] = dv end
             end
         end
         -- Unknown JSON keys are silently ignored (per spec).
diff --git a/test/conformance/known_failures.txt b/test/conformance/known_failures.txt
index 81377d55fb2bbe3be55c10d6378407101e1034e4..c97776fcf23eb0cce2a3798e736fe0aeb963899b 100644
--- a/test/conformance/known_failures.txt
+++ b/test/conformance/known_failures.txt
@@ -19,11 +19,6 @@
 #
 # Re-generate this file after fixes via `just conformance-refresh-failures`.
 Recommended.Proto3.JsonInput.FieldNameWithDoubleUnderscores.ProtobufOutput
-Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInMapPart.ProtobufOutput
-Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInMapValue.ProtobufOutput
-Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInOptionalField.ProtobufOutput
-Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInRepeatedField.ProtobufOutput
-Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInRepeatedPart.ProtobufOutput
 Recommended.Proto3.JsonInput.NullValueInOtherOneofOldFormat.Validator
 Recommended.Proto3.ProtobufInput.RejectInvalidUtf8.String.MapKey
 Recommended.Proto3.ProtobufInput.RejectInvalidUtf8.String.MapValue