[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

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();

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();

lldb/unittests/debugserver/CMakeLists.txt

@@ -8,6 +8,7 @@ include_directories(${LLDB_SOURCE_DIR}/tools/debugserver/source
                     ${LLDB_SOURCE_DIR}/tools/debugserver/source/MacOSX)
 
 add_lldb_unittest(debugserverTests
+  JSONTest.cpp
   RNBSocketTest.cpp
   debugserver_LogCallback.cpp
 
@@ -24,8 +25,9 @@ if(IOS)
       WITH_FBS
       WITH_BKS
       )
-  
+
   add_lldb_unittest(debugserverNonUITests
+    JSONTest.cpp
     RNBSocketTest.cpp
     debugserver_LogCallback.cpp
 

lldb/unittests/debugserver/JSONTest.cpp

@@ -0,0 +1,89 @@
+//===-- JSONTest.cpp --------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+#include "JSON.h"
+
+template <typename T>
+void TestJSON(JSONValue *json_val, const std::function<void(T &)> &test_func) {
+  ASSERT_THAT(json_val, testing::NotNull());
+  ASSERT_TRUE(T::classof(json_val));
+  test_func(static_cast<T &>(*json_val));
+}
+
+JSONValue::SP ParseJSON(const char *json_string) {
+  return JSONParser(json_string).ParseJSONValue();
+}
+
+template <typename T>
+void ParseAndTestJSON(
+    const char *json_string,
+    const std::function<void(T &)> &test_func = [](T &) {}) {
+  auto json_val = ParseJSON(json_string);
+  TestJSON<T>(json_val.get(), test_func);
+}
+
+TEST(JSON, Parse) {
+  ParseAndTestJSON<JSONString>("\"foo\"", [](JSONString &string_val) {
+    EXPECT_EQ(string_val.GetData(), "foo");
+  });
+  EXPECT_THAT(ParseJSON("\"foo"), testing::IsNull());
+  ParseAndTestJSON<JSONNumber>("3", [](JSONNumber &number_val) {
+    EXPECT_EQ(number_val.GetAsSigned(), 3);
+    EXPECT_EQ(number_val.GetAsUnsigned(), 3u);
+    EXPECT_EQ(number_val.GetAsDouble(), 3.0);
+  });
+  ParseAndTestJSON<JSONNumber>("-5", [](JSONNumber &number_val) {
+    EXPECT_EQ(number_val.GetAsSigned(), -5);
+    EXPECT_EQ(number_val.GetAsDouble(), -5.0);
+  });
+  ParseAndTestJSON<JSONNumber>("-6.4", [](JSONNumber &number_val) {
+    EXPECT_EQ(number_val.GetAsSigned(), -6);
+    EXPECT_EQ(number_val.GetAsDouble(), -6.4);
+  });
+  EXPECT_THAT(ParseJSON("-1.2.3"), testing::IsNull());
+  ParseAndTestJSON<JSONTrue>("true");
+  ParseAndTestJSON<JSONFalse>("false");
+  ParseAndTestJSON<JSONNull>("null");
+  ParseAndTestJSON<JSONObject>(
+      "{ \"key1\": 4, \"key2\": \"foobar\" }", [](JSONObject &obj_val) {
+        TestJSON<JSONNumber>(obj_val.GetObject("key1").get(),
+                             [](JSONNumber &number_val) {
+                               EXPECT_EQ(number_val.GetAsSigned(), 4);
+                               EXPECT_EQ(number_val.GetAsUnsigned(), 4u);
+                               EXPECT_EQ(number_val.GetAsDouble(), 4.0);
+                             });
+        TestJSON<JSONString>(obj_val.GetObject("key2").get(),
+                             [](JSONString &string_val) {
+                               EXPECT_EQ(string_val.GetData(), "foobar");
+                             });
+      });
+  ParseAndTestJSON<JSONArray>("[1, \"bar\", 3.14]", [](JSONArray &array_val) {
+    EXPECT_EQ(array_val.GetNumElements(), 3u);
+    TestJSON<JSONNumber>(array_val.GetObject(0).get(),
+                         [](JSONNumber &number_val) {
+                           EXPECT_EQ(number_val.GetAsSigned(), 1);
+                           EXPECT_EQ(number_val.GetAsUnsigned(), 1u);
+                           EXPECT_EQ(number_val.GetAsDouble(), 1.0);
+                         });
+    TestJSON<JSONString>(
+        array_val.GetObject(1).get(),
+        [](JSONString &string_val) { EXPECT_EQ(string_val.GetData(), "bar"); });
+    TestJSON<JSONNumber>(array_val.GetObject(2).get(),
+                         [](JSONNumber &number_val) {
+                           EXPECT_EQ(number_val.GetAsSigned(), 3);
+                           EXPECT_EQ(number_val.GetAsUnsigned(), 3u);
+                           EXPECT_EQ(number_val.GetAsDouble(), 3.14);
+                         });
+  });
+  ParseAndTestJSON<JSONArray>("[]", [](JSONArray &array_val) {
+    EXPECT_EQ(array_val.GetNumElements(), 0u);
+  });
+}