[clang] [analyzer] Add an ownership change visitor to StreamChecker (PR #94957)

[Donát Nagy via cfe-commits]

================
@@ -696,6 +732,69 @@ struct StreamOperationEvaluator {
 
 } // end anonymous namespace
 
+//===----------------------------------------------------------------------===//
+// Definition of NoStreamStateChangeVisitor.
+//===----------------------------------------------------------------------===//
+
+namespace {
+class NoStreamStateChangeVisitor final : public NoOwnershipChangeVisitor {
+protected:
+  /// Syntactically checks whether the callee is a freeing function. Since
+  /// we have no path-sensitive information on this call (we would need a
+  /// CallEvent instead of a CallExpr for that), its possible that a
+  /// freeing function was called indirectly through a function pointer,
+  /// but we are not able to tell, so this is a best effort analysis.
+  bool isFreeingCallAsWritten(const CallExpr &Call) const {
+    const auto *StreamChk = static_cast<const StreamChecker *>(&Checker);
+    if (StreamChk->FCloseDesc.matchesAsWritten(Call))
+      return true;
+
+    return false;
+  }
+
+  bool doesFnIntendToHandleOwnership(const Decl *Callee,
+                                     ASTContext &ACtx) override {
+    using namespace clang::ast_matchers;
+    const FunctionDecl *FD = dyn_cast<FunctionDecl>(Callee);
+
+    auto Matches =
+        match(findAll(callExpr().bind("call")), *FD->getBody(), ACtx);
+    for (BoundNodes Match : Matches) {
+      if (const auto *Call = Match.getNodeAs<CallExpr>("call"))
+        if (isFreeingCallAsWritten(*Call))
+          return true;
+    }
+    // TODO: Ownership might change with an attempt to store stream object, not
+    // only through freeing it. Check for attempted stores as well.
+    return false;
+  }
+
+  virtual bool hasResourceStateChanged(ProgramStateRef CallEnterState,
+                                       ProgramStateRef CallExitEndState) final {
+    return CallEnterState->get<StreamMap>(Sym) !=
+           CallExitEndState->get<StreamMap>(Sym);
+  }
+
+  PathDiagnosticPieceRef emitNote(const ExplodedNode *N) override {
+    PathDiagnosticLocation L = PathDiagnosticLocation::create(
+        N->getLocation(),
+        N->getState()->getStateManager().getContext().getSourceManager());
+    return std::make_shared<PathDiagnosticEventPiece>(
+        L, "Returning without freeing stream object or storing the pointer for "
----------------
NagyDonat wrote:

```suggestion
        L, "Returning without freeing stream object or storing it for "
```
The current phrasing is technically correct, because the stream object is a `FILE *` _pointer_, but IMO "it" would be both shorter and easier to understand

https://github.com/llvm/llvm-project/pull/94957