[lldb] Fix JSON parser to allow empty arrays

Summary:
Bugzilla: https://bugs.llvm.org/show_bug.cgi?id=39405
```
alexc@kitty:~/work/wiredtiger/build_posix$ cat breakpoint.json
[{"Breakpoint" : {"BKPTOptions" : {"AutoContinue" : false,"ConditionText" : "","EnabledState" : true,"IgnoreCount" : 0,"OneShotState" : false},"BKPTResolver" : {"Options" : {"NameMask" : [56],"Offset" : 0,"SkipPrologue" : true,"SymbolNames" : ["__wt_btcur_search"]},"Type" : "SymbolName"},"Hardware" : false,"SearchFilter" : {"Options" : {},"Type" : "Unconstrained","Foo" : []}}}]
```
**Before**
```
(lldb) breakpoint read --file breakpoint.json
error: Invalid JSON from input file: /home/alexc/work/wiredtiger/build_posix/breakpoint.json.
```
**After**
```
(lldb) breakpoint read --file breakpoint.json
New breakpoints:
Breakpoint 1: where = libwiredtiger-3.2.2.so`__wt_btcur_search + 15 at bt_cursor.c:522:5, address = 0x00007ffff576ab2f
```

Reviewers: xbolva00, davide, labath

Reviewed By: davide, labath

Subscribers: mgorny, jingham, labath, davide, JDevlieghere, lldb-commits

Tags: #llvm, #lldb

Differential Revision: https://reviews.llvm.org/D68179

2 files changed, 12 insertions, 2 deletions

diff --git a/lldb/tools/debugserver/source/JSON.cpp b/lldb/tools/debugserver/source/JSON.cpp
index 1b37767256d..12d96d4ed4d 100644
--- a/lldb/tools/debugserver/source/JSON.cpp
+++ b/lldb/tools/debugserver/source/JSON.cpp
@@ -516,13 +516,16 @@ JSONValue::SP JSONParser::ParseJSONArray() {
   std::string value;
   std::string key;
   while (true) {
-    JSONValue::SP value_sp = ParseJSONValue();
+    JSONParser::Token token = GetToken(value);
+    if (token == JSONParser::Token::ArrayEnd)
+      return JSONValue::SP(array_up.release());
+    JSONValue::SP value_sp = ParseJSONValue(value, token);
     if (value_sp)
       array_up->AppendObject(value_sp);
     else
       break;
 
-    JSONParser::Token token = GetToken(value);
+    token = GetToken(value);
     if (token == JSONParser::Token::Comma) {
       continue;
     } else if (token == JSONParser::Token::ArrayEnd) {
@@ -537,6 +540,11 @@ JSONValue::SP JSONParser::ParseJSONArray() {
 JSONValue::SP JSONParser::ParseJSONValue() {
   std::string value;
   const JSONParser::Token token = GetToken(value);
+  return ParseJSONValue(value, token);
+}
+
+JSONValue::SP JSONParser::ParseJSONValue(const std::string &value,
+                                         const Token &token) {
   switch (token) {
   case JSONParser::Token::ObjectStart:
     return ParseJSONObject();
diff --git a/lldb/tools/debugserver/source/JSON.h b/lldb/tools/debugserver/source/JSON.h
index b1c4a4c9db8..70bfdd7259a 100644
--- a/lldb/tools/debugserver/source/JSON.h
+++ b/lldb/tools/debugserver/source/JSON.h
@@ -292,6 +292,8 @@ public:
   JSONValue::SP ParseJSONValue();
 
 protected:
+  JSONValue::SP ParseJSONValue(const std::string &value, const Token &token);
+
   JSONValue::SP ParseJSONObject();
 
   JSONValue::SP ParseJSONArray();