{"id":31902,"date":"2023-03-03T16:00:07","date_gmt":"2023-03-03T16:00:07","guid":{"rendered":"https:\/\/devblogs.microsoft.com\/cppblog\/?p=31902"},"modified":"2023-03-03T09:05:26","modified_gmt":"2023-03-03T09:05:26","slug":"code-analysis-improvements-in-visual-studio-17-6","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/cppblog\/code-analysis-improvements-in-visual-studio-17-6\/","title":{"rendered":"Code Analysis Improvements in Visual Studio 17.6"},"content":{"rendered":"

The C++ team is committed to making your C++ coding experience as safe as possible. We are adding richer code safety checks and addressing high impact customer feedback bugs posted on the C++ Developer Community<\/a>\u202fpage. Thank you for engaging with us and giving us great feedback on the past releases and early previews leading to this point. Below is the detailed overview of the improvements we made to our code analysis tools.<\/p>\n

Improvements to existing checks<\/h2>\n

We improved many checks to find more errors and emit fewer false positives. This section contains some highlights of the work we did over the past months.<\/p>\n

Unwrapping empty std::optionals<\/h3>\n

The initial version of C26830<\/a>, which checks for the safe unwrapping of std::optional<\/code>, did not support the operator==<\/code> free function and reported a false C26830 for the code below:<\/p>\n

int f(std::optional<int> o) {\r\n  if (o == std::nullopt)\r\n      return 42;\r\n  \/\/ Previously, C26830 was emitted below.\r\n  return *o;\r\n}<\/code><\/pre>\n
After our improvements the analyzer no longer warns on the code above. This addition can also help finding more problems when a condition is accidentally inverted:<\/p>\n
int f(std::optional<int> o) {\r\n  if (o != std::nullopt)\r\n    return 42;\r\n  return *o; \/\/ C26829 emitted.\r\n}<\/code><\/pre>\n
We relaxed C26829<\/a> and C26830<\/a> to not warn when the value<\/code> method is invoked on a potentially empty std::optional<\/code>. Calling value<\/code> on an empty optional will raise an exception, which some users prefer to catch instead of checking for emptiness upfront. When this exception is unacceptable, we introduced C26859<\/a> and C26860<\/a>, which forces an explicit null-check, guaranteeing that no exception is thrown. This was a request from this DevCom ticket<\/a>.<\/p>\n
Support conditional moves<\/h3>\n
Some APIs in the STL will consume an argument in some cases but leave it unchanged in others. Previously, the use use after move check<\/a> assumed that these select APIs will always<\/em> consume the argument. We improved the check to better understand some commonly used APIs in the STL and avoid emitting false positives. For example, the following code snippet will no longer trigger any warnings:<\/p>\n
int f() {\r\n  std::map<int, MyType> myMap;\r\n  MyType val;\r\n  auto emplaceResult = myMap.try_emplace(1, std::move(val));\r\n  if (!emplaceResult.second) { \/\/ val was not inserted into the map\r\n    val.method(); \/\/ Previously, C26800 was emitted.\r\n  }\r\n}<\/code><\/pre>\n
In this code snippet, when the second element of the returned pair is false, val<\/code> was not consumed by try_emplace<\/code>. In that scenario, it is safe to use val<\/code>. This problem was reported in a DevCom ticket<\/a>.<\/p>\n
Other improvements<\/h3>\n
We also made many smaller improvements to other existing checks including:<\/p>\n