[clang] [clang][analyzer][NFC] Supplement comments in `evalFtell` of StreamChecker (PR #74291)

[Ben Shi via cfe-commits]

https://github.com/benshi001 created https://github.com/llvm/llvm-project/pull/74291

None

>From 2b8903b380c38c2d7f50491da75cec25ff4b801c Mon Sep 17 00:00:00 2001
From: Ben Shi <bennshi at tencent.com>
Date: Mon, 4 Dec 2023 16:41:46 +0800
Subject: [PATCH] [clang][analyzer][NFC] Supplement comments in `evalFtell` of
 the StreamChecker

---
 clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp
index a4799b5f762ca..925fc90e35543 100644
--- a/clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp
@@ -1072,6 +1072,9 @@ void StreamChecker::evalFtell(const FnDescription *Desc, const CallEvent &Call,
   ProgramStateRef StateFailed = State->BindExpr(
       CE, C.getLocationContext(), SVB.makeIntVal(-1, C.getASTContext().LongTy));
 
+  // This function does not affect the stream state.
+  // Still we add success and failure state with the appropriate return value.
+  // StdLibraryFunctionsChecker can change these states (set the 'errno' state).
   C.addTransition(StateNotFailed);
   C.addTransition(StateFailed);
 }