Skip to content

[clang] Check captured variables for noreturn attribute #155213

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 2 commits into
base: main
Choose a base branch
from
Open

[clang] Check captured variables for noreturn attribute #155213

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
52499a2
[clang] Check captured variables for noreturn attribute
spavloff Aug 25, 2025
8c258f4
Addressreview notes
spavloff Sep 17, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
35 changes: 35 additions & 0 deletions clang/lib/Sema/AnalysisBasedWarnings.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -467,6 +467,41 @@ struct TransferFunctions : public StmtVisitor<TransferFunctions> {
AllValuesAreNoReturn = false;
}
}

void VisitCXXOperatorCallExpr(CXXOperatorCallExpr *CE) {
if (CE->getOperator() == OO_Call && CE->getNumArgs() > 0) {
Expr *Obj = CE->getArg(0)->IgnoreParenCasts();
if (auto *MTE = dyn_cast<MaterializeTemporaryExpr>(Obj))
Obj = MTE->getSubExpr();
if (auto *DRE = dyn_cast<DeclRefExpr>(Obj)) {
auto *D = dyn_cast<VarDecl>(DRE->getDecl());
if (D->hasInit())
Obj = D->getInit();
}
Visit(Obj);
}
}

void VisitLambdaExpr(LambdaExpr *LE) {
for (const LambdaCapture &Capture : LE->captures())
if (Capture.capturesVariable())
if (const VarDecl *VD = dyn_cast<VarDecl>(Capture.getCapturedVar()))
if (VD == Var)
if (Capture.getCaptureKind() == LCK_ByRef)
AllValuesAreNoReturn = false;
}

void VisitMaterializeTemporaryExpr(MaterializeTemporaryExpr *MTE) {
Visit(MTE->getSubExpr());
}

void VisitExprWithCleanups(FullExpr *FE) {
Visit(FE->getSubExpr());
}

void VisitCXXConstructExpr(CXXConstructExpr *CE) {
Visit(CE->getArg(0));
Copy link
Collaborator

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This doesn't seem right at all. the 'this' argument in a CXXConstructExpr does NOT get placed in the 0 arg (in fact, they are not present), so you can't assume 0 exists here. AND it isn't really clear why the 0 arg is important here, but others arent?

Copy link
Collaborator Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

It is more about the way LambdaExpr can be reached from variable initializer. For example, the code:

auto LF = [&func_ptr]() { func_ptr = ordinary; };

produces AST like:

DeclStmt 0x129e8159a10 <line:10:3, col:72>
`-VarDecl 0x129e812a478 <col:3, col:71> col:8 used LF '(lambda at zz-01.cpp:10:13)' cinit
  `-ExprWithCleanups 0x129e81599f8 <col:13, col:71> '(lambda at zz-01.cpp:10:13)'
    `-CXXConstructExpr 0x129e81599c8 <col:13, col:71> '(lambda at zz-01.cpp:10:13)' 'void ((lambda at zz-01.cpp:10:13) &&) noexcept' elidable
      `-MaterializeTemporaryExpr 0x129e8159728 <col:13, col:71> '(lambda at zz-01.cpp:10:13)' xvalue
        `-LambdaExpr 0x129e812aa78 <col:13, col:71> '(lambda at zz-01.cpp:10:13)'

These 'Visit*' methods are introduced to support this kind of lambda usage.

}
};
} // namespace

Expand Down
13 changes: 13 additions & 0 deletions clang/test/SemaCXX/noreturn-vars.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -225,3 +225,16 @@ extern void abc_02(func_type *);
abc_02(&func_ptr);
func_ptr();
} // expected-warning {{function declared 'noreturn' should not return}}

[[noreturn]] void test_lambda() {
func_type func_ptr = noret;
[&func_ptr]() { func_ptr = ordinary; } ();
func_ptr();
} // expected-warning {{function declared 'noreturn' should not return}}

[[noreturn]] void test_lambda_var(int x) {
func_type func_ptr = noret;
auto LF = [&](){func_ptr = ordinary;};
Copy link
Collaborator

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Would like to see a test for member functions here as well. Also, test that shows capture-by-value doesn't cause this diagnostic.

Copy link
Collaborator Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The added test lambda_capture_by_value checks capture by value. As for member functions, capture of this as in the example:

class LambdaTest_1 {
  func_type func_ptr = noret;  
  [[noreturn]] void method() {
    auto LF = [this](){ return func_ptr; };
    LF();
    func_ptr();
  } // expected-warning {{function declared 'noreturn' should not return}}
};

the captured variables are represented by member expressions rather that references to variables This case requires more complex analysis that the current, it can be implemented in future.

LF();
func_ptr();
} // expected-warning {{function declared 'noreturn' should not return}}
Loading