[clang] [clang][analyzer] Add function 'ungetc' to StreamChecker. (PR #77331)

[Balazs Benics via cfe-commits]

=?utf-8?q?Balázs_Kéri?= <balazs.keri at ericsson.com>,
=?utf-8?q?Balázs_Kéri?= <balazs.keri at ericsson.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/77331 at github.com>


================
@@ -916,6 +922,45 @@ void StreamChecker::evalFputx(const FnDescription *Desc, const CallEvent &Call,
   C.addTransition(StateFailed);
 }
 
+void StreamChecker::evalUngetc(const FnDescription *Desc, const CallEvent &Call,
+                               CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+  SymbolRef StreamSym = getStreamArg(Desc, Call).getAsSymbol();
+  if (!StreamSym)
+    return;
+
+  const CallExpr *CE = dyn_cast_or_null<CallExpr>(Call.getOriginExpr());
+  if (!CE)
+    return;
+
+  const StreamState *OldSS = State->get<StreamMap>(StreamSym);
+  if (!OldSS)
+    return;
+
+  assertStreamStateOpened(OldSS);
+
+  // Generate a transition for the success state.
+  std::optional<NonLoc> PutVal = Call.getArgSVal(0).getAs<NonLoc>();
+  if (!PutVal)
+    return;
+  ProgramStateRef StateNotFailed =
+      State->BindExpr(CE, C.getLocationContext(), *PutVal);
+  StateNotFailed =
+      StateNotFailed->set<StreamMap>(StreamSym, StreamState::getOpened(Desc));
+  C.addTransition(StateNotFailed);
+
+  // Add transition for the failed state.
+  // Failure of 'ungetc' does not result in feof or ferror state.
+  // If the PutVal has value of EofVal the function should "fail", but this is
+  // the same transition as the success state.
+  // In this case only one state transition is added by the analyzer (the two
+  // new states may be similar).
+  ProgramStateRef StateFailed = bindInt(*EofVal, State, C, CE);
+  StateFailed =
+      StateFailed->set<StreamMap>(StreamSym, StreamState::getOpened(Desc));
+  C.addTransition(StateFailed);
----------------
steakhal wrote:

Why did we not set `ErrorFError | ErrorFEof` errors for the failure state?

https://github.com/llvm/llvm-project/pull/77331