Merge #18444: RPC: Remove final comma for last entry of fixed-size arrays/objects in RPCResult

c341648 Bugfix: RPC: Remove final comma for last entry of fixed-size Arrays and Objects in RPCResult (Luke Dashjr)

Pull request description:

  JSON doesn't allow a trailing comma in arrays

Top commit has no ACKs.

Tree-SHA512: 761502a05f447afc09c120f13bf23abd2aee83a7f5e5dadaf54c7e1c0c1280d83ee041ca6ca45998fb561e41b32d01067ec52a187c3bcc9d53303ea813bc212c

Author: MarcoFalke

src/rpc/util.cpp

@@ -293,7 +293,7 @@ UniValue JSONRPCTransactionError(TransactionError terr, const std::string& err_s
 struct Section {
     Section(const std::string& left, const std::string& right)
         : m_left{left}, m_right{right} {}
-    const std::string m_left;
+    std::string m_left;
     const std::string m_right;
 };
 
@@ -645,6 +645,10 @@ void RPCResult::ToSections(Sections& sections, const OuterType outer_type, const
         }
         if (m_type == Type::ARR) {
             sections.PushSection({indent_next + "...", ""});
+        } else {
+            CHECK_NONFATAL(!m_inner.empty());
+            // Remove final comma, which would be invalid JSON
+            sections.m_sections.back().m_left.pop_back();
         }
         sections.PushSection({indent + "]" + maybe_separator, ""});
         return;
@@ -658,6 +662,10 @@ void RPCResult::ToSections(Sections& sections, const OuterType outer_type, const
         if (m_type == Type::OBJ_DYN) {
             // If the dictionary keys are dynamic, use three dots for continuation
             sections.PushSection({indent_next + "...", ""});
+        } else {
+            CHECK_NONFATAL(!m_inner.empty());
+            // Remove final comma, which would be invalid JSON
+            sections.m_sections.back().m_left.pop_back();
         }
         sections.PushSection({indent + "}" + maybe_separator, ""});
         return;