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Suppress noreturn warning if last statement in a function is a throw #145166
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@llvm/pr-subscribers-clang Author: Samarth Narang (snarang181) ChangesFull diff: https://github.com/llvm/llvm-project/pull/145166.diff 2 Files Affected:
diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 2a107a36e24b4..85a5d99c710d5 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -626,6 +626,31 @@ struct CheckFallThroughDiagnostics {
} // anonymous namespace
+static bool isKnownToAlwaysThrow(const FunctionDecl *FD) {
+ if (!FD->hasBody())
+ return false;
+ const Stmt *Body = FD->getBody();
+ const Stmt *OnlyStmt = nullptr;
+
+ if (const auto *Compound = dyn_cast<CompoundStmt>(Body)) {
+ if (Compound->size() != 1)
+ return false; // More than one statement, can't be known to always throw.
+ OnlyStmt = *Compound->body_begin();
+ } else {
+ OnlyStmt = Body;
+ }
+
+ // Unwrap ExprWithCleanups if necessary.
+ if (const auto *EWC = dyn_cast<ExprWithCleanups>(OnlyStmt)) {
+ OnlyStmt = EWC->getSubExpr();
+ }
+ // Check if the only statement is a throw expression.
+ if (isa<CXXThrowExpr>(OnlyStmt)) {
+ return true; // Known to always throw.
+ }
+ return false; // Not known to always throw.
+}
+
/// CheckFallThroughForBody - Check that we don't fall off the end of a
/// function that should return a value. Check that we don't fall off the end
/// of a noreturn function. We assume that functions and blocks not marked
@@ -681,6 +706,26 @@ static void CheckFallThroughForBody(Sema &S, const Decl *D, const Stmt *Body,
if (CD.diag_FallThrough_HasNoReturn)
S.Diag(RBrace, CD.diag_FallThrough_HasNoReturn) << CD.FunKind;
} else if (!ReturnsVoid && CD.diag_FallThrough_ReturnsNonVoid) {
+ // If the final statement is a call to an always-throwing function,
+ // don't warn about the fall-through.
+ if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
+ if (const auto *CS = dyn_cast<CompoundStmt>(Body)) {
+ if (!CS->body_empty()) {
+ const Stmt *LastStmt = CS->body_back();
+ // Unwrap ExprWithCleanups if necessary.
+ if (const auto *EWC = dyn_cast<ExprWithCleanups>(LastStmt)) {
+ LastStmt = EWC->getSubExpr();
+ }
+ if (const auto *CE = dyn_cast<CallExpr>(LastStmt)) {
+ if (const FunctionDecl *Callee = CE->getDirectCallee()) {
+ if (isKnownToAlwaysThrow(Callee)) {
+ return; // Don't warn about fall-through.
+ }
+ }
+ }
+ }
+ }
+ }
bool NotInAllControlPaths = FallThroughType == MaybeFallThrough;
S.Diag(RBrace, CD.diag_FallThrough_ReturnsNonVoid)
<< CD.FunKind << NotInAllControlPaths;
diff --git a/clang/test/SemaCXX/wreturn-always-throws.cpp b/clang/test/SemaCXX/wreturn-always-throws.cpp
new file mode 100644
index 0000000000000..0bbce0f5c1871
--- /dev/null
+++ b/clang/test/SemaCXX/wreturn-always-throws.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -fsyntax-only -fcxx-exceptions -fexceptions -Wreturn-type -verify %s
+// expected-no-diagnostics
+
+namespace std {
+ class string {
+ public:
+ string(const char*); // constructor for runtime_error
+ };
+ class runtime_error {
+ public:
+ runtime_error(const string &);
+ };
+}
+
+void throwError(const std::string& msg) {
+ throw std::runtime_error(msg);
+}
+
+int ensureZero(const int i) {
+ if (i == 0) return 0;
+ throwError("ERROR"); // no-warning
+}
|
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Pull Request Overview
This PR adds support to suppress “fall-through” return-type warnings when a function’s last statement always throws, along with a verifying test.
- Introduce
isKnownToAlwaysThrow
helper to detect single-statement throw functions - Update
CheckFallThroughForBody
to skip warnings for calls to those functions - Add a new test (
wreturn-always-throws.cpp
) to verify suppression
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.
File | Description |
---|---|
clang/test/SemaCXX/wreturn-always-throws.cpp | New test covering a non-void function that ends in a throw |
clang/lib/Sema/AnalysisBasedWarnings.cpp | Helper and logic to suppress return-type warnings on throwers |
if (const auto *EWC = dyn_cast<ExprWithCleanups>(LastStmt)) { | ||
LastStmt = EWC->getSubExpr(); | ||
} |
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[nitpick] The unwrap of ExprWithCleanups
is duplicated in two places. Consider extracting a helper function to reduce duplication and centralize cleanup unwrapping logic.
if (const auto *EWC = dyn_cast<ExprWithCleanups>(LastStmt)) { | |
LastStmt = EWC->getSubExpr(); | |
} | |
LastStmt = unwrapExprWithCleanups(LastStmt); |
Copilot uses AI. Check for mistakes.
✅ With the latest revision this PR passed the C/C++ code formatter. |
Co-authored-by: Copilot <[email protected]>
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Thank you for the patch! Please add a release note in clang/docs/ReleaseNotes.rst
.
I'm not sure if this case should be handled:
if (condition) {
throw 1;
} else {
throw 2;
}
Maybe we need to open an issue for it.
Add a note in the release notes about the fix for the no-return function warning
@zwuis, added a description of the patch in the release notes and addressed your review comments. |
Fixes #144952