[clang] [NFC][Static Analyzer] Rename and discuss about `NotNullConstraint` & `NotNullBufferConstraint` (PR #131374)

[Balázs Kéri via cfe-commits]

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@@ -1165,7 +1165,7 @@ ProgramStateRef StdLibraryFunctionsChecker::NotNullConstraint::apply(
   return State->assume(L, CannotBeNull);
 }
 
-void StdLibraryFunctionsChecker::NotNullConstraint::describe(
+void StdLibraryFunctionsChecker::NullnessConstraint::describe(
     DescriptionKind DK, const CallEvent &Call, ProgramStateRef State,
     const Summary &Summary, llvm::raw_ostream &Out) const {
   assert(CannotBeNull &&
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balazske wrote:

The `describeArgumentValue` should be really called only with a `ProgramState` where the current constraint is true. The purpose is to generate a description of the actual value and probably use the program state for this. It is exactly used on the negated version of a failed constraint in `reportBug`.

https://github.com/llvm/llvm-project/pull/131374