[clang] [analyzer] Add documentation for std::variant checker (PR #76501)

[Gábor Spaits via cfe-commits]

https://github.com/spaits created https://github.com/llvm/llvm-project/pull/76501

Add a short documentation for `StdVariantChecker`.

>From f7f26c38d1d363bf1dd097dc73e004970dfb32df Mon Sep 17 00:00:00 2001
From: Gabor Spaits <gaborspaits1 at gmail.com>
Date: Thu, 28 Dec 2023 14:17:55 +0100
Subject: [PATCH] [analyzer] Add documentation for std::variant checker

---
 clang/docs/analyzer/checkers.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/clang/docs/analyzer/checkers.rst b/clang/docs/analyzer/checkers.rst
index 81d40395067c9a..1e5ba013f85d67 100644
--- a/clang/docs/analyzer/checkers.rst
+++ b/clang/docs/analyzer/checkers.rst
@@ -2097,6 +2097,18 @@ This checker is a part of ``core.StackAddressEscape``, but is temporarily disabl
 
 .. _alpha-core-TestAfterDivZero:
 
+alpha.core.StdVariant (C++)
+"""""""""""""""""""""""
+Check if the active value accessed in an ``std::variant`` instance.
+.. code-block:: cpp
+
+ void test() {
+   std::variant <int, char> v = 25;
+   char c = stg::get<char>(v); // warn
+ }
+
+.. _alpha-core-StdVariant:
+
 alpha.core.TestAfterDivZero (C)
 """""""""""""""""""""""""""""""
 Check for division by variable that is later compared against 0.