[clang] [clang][analyzer] Support `fflush` in the StreamChecker (PR #74296)

[Balázs Kéri via cfe-commits]

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@@ -1191,6 +1199,84 @@ void StreamChecker::evalSetFeofFerror(const FnDescription *Desc,
   C.addTransition(State);
 }
 
+void StreamChecker::preFflush(const FnDescription *Desc, const CallEvent &Call,
+                              CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+  SVal StreamVal = getStreamArg(Desc, Call);
+  std::optional<DefinedSVal> Stream = StreamVal.getAs<DefinedSVal>();
+  SymbolRef StreamSym = StreamVal.getAsSymbol();
+  if (!Stream || !StreamSym)
+    return;
+
+  ProgramStateRef StateNotNull, StateNull;
+  std::tie(StateNotNull, StateNull) =
+      C.getConstraintManager().assumeDual(State, *Stream);
+  if (StateNotNull) {
+    if (StateNotNull = ensureStreamOpened(StreamVal, C, StateNotNull))
+      C.addTransition(StateNotNull);
+  } else if (StateNull) {
+    const StreamState *SS = StateNull->get<StreamMap>(StreamSym);
+    if (!SS || !SS->isOpenFailed()) {
+      StateNull = StateNull->set<StreamMap>(StreamSym,
+                                            StreamState::getOpenFailed(Desc));
+      if (StateNull)
+        C.addTransition(StateNull);
+    }
+  }
+}
+
+void StreamChecker::evalFflush(const FnDescription *Desc, const CallEvent &Call,
+                               CheckerContext &C) const {
+  ProgramStateRef State = C.getState();
+  SymbolRef StreamSym = getStreamArg(Desc, Call).getAsSymbol();
+  const StreamState *SS = nullptr;
+
+  // Skip if the input stream's state is unknown.
+  // FIXME: We should skip non-NULL constant, such as `(FILE *) 0x1234`.
+  if (StreamSym) {
+    if (!(SS = State->get<StreamMap>(StreamSym)))
+      return;
+    assert((SS->isOpened() || SS->isOpenFailed()) &&
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balazske wrote:

An open-failed stream is not acceptable here, it must be opened only.

https://github.com/llvm/llvm-project/pull/74296