value_util.cc: Fix MaxValue() to no longer use designated initialization.

[dconeybe]

In #9750, the implementation of MaxValue() in value_util.cc was changed to avoid heap memory allocation that leaked memory. The fix created global variables so that the memory had static storage duration. However, these global variables used a C++20 feature called designated initialization, and this code base only supports C++11.

I originally tried to change the designated initialization to aggregate initialization; however, one of the global variables had a "union" member variable that cannot be initialized with aggregate initialization because "when a union is initialized by aggregate initialization, only its first non-static data member is initialized" and the member to be initialized was not the first member.

So I just changed the implementation of MaxValue() to basically what it was before #9750, except that the object that was being allocated on the heap via a call to calloc() is now allocated in static storage. This should make ASAN happy while also fixing the invalid usage of designated initialization.

This bug was detected by a downstream build that was more strict and failed due to the use of a C++20 feature in a C++11 code base: firebase/firebase-cpp-sdk#967 (comment)

#no-changelog

[google-oss-bot]

Coverage Report ¹

Affected Products

• FirebaseFirestore-iOS-FirebaseFirestore.framework

  Overall coverage changed from 88.38% (68bc0b5) to 88.42% (0ec99c5) by +0.05%.

  Filename	Base (68bc0b5)	Merge (0ec99c5)	Diff
  document.nanopb.cc	96.52%	98.26%	+1.74%
  leveldb_key.cc	98.14%	98.63%	+0.49%
  ordered_code.cc	93.90%	94.39%	+0.49%
  value_util.cc	95.59%	95.67%	+0.09%

Test Logs

• Base (68bc0b5): https://github.com/firebase/firebase-ios-sdk/actions/runs/2396994098
• Merge (0ec99c5): https://github.com/firebase/firebase-ios-sdk/actions/runs/2396999244

1. https://storage.googleapis.com/firebase-sdk-metric-reports/Xb8DQU48yd.html

[google-oss-bot]

Size Report ¹

Affected Products

• FirebaseFirestore

  Type	Base (68bc0b5)	Merge (0ec99c5)	Diff
  CocoaPods	?	6.89 MB	? (?)

Test Logs

• Merge (0ec99c5): https://github.com/firebase/firebase-ios-sdk/actions/runs/2396999244

1. https://storage.googleapis.com/firebase-sdk-metric-reports/Pkp6e4513l.html