[clang-tidy] Model noexcept more properly in bugprone-exception-escape

During call stack analysis skip called noexcept functions
as they wont throw exceptions, they will crash.
Check will emit warnings for those functions separately.

Fixes: #43667, #49151, #51596, #54668, #54956

Reviewed By: carlosgalvezp

Differential Revision: https://reviews.llvm.org/D153458

clang-tools-extra/clang-tidy/utils/ExceptionAnalyzer.cpp

@@ -316,6 +316,34 @@ bool isQualificationConvertiblePointer(QualType From, QualType To,
 }
 } // namespace
 
+static bool canThrow(const FunctionDecl *Func) {
+  const auto *FunProto = Func->getType()->getAs<FunctionProtoType>();
+  if (!FunProto)
+    return true;
+
+  switch (FunProto->canThrow()) {
+  case CT_Cannot:
+    return false;
+  case CT_Dependent: {
+    const Expr *NoexceptExpr = FunProto->getNoexceptExpr();
+    if (!NoexceptExpr)
+      return true; // no noexept - can throw
+
+    if (NoexceptExpr->isValueDependent())
+      return true; // depend on template - some instance can throw
+
+    bool Result = false;
+    if (!NoexceptExpr->EvaluateAsBooleanCondition(Result, Func->getASTContext(),
+                                                  /*InConstantContext=*/true))
+      return true;  // complex X condition in noexcept(X), cannot validate,
+                    // assume that may throw
+    return !Result; // noexcept(false) - can throw
+  }
+  default:
+    return true;
+  };
+}
+
 bool ExceptionAnalyzer::ExceptionInfo::filterByCatch(
     const Type *HandlerTy, const ASTContext &Context) {
   llvm::SmallVector<const Type *, 8> TypesToDelete;
@@ -421,7 +449,7 @@ void ExceptionAnalyzer::ExceptionInfo::reevaluateBehaviour() {
 ExceptionAnalyzer::ExceptionInfo ExceptionAnalyzer::throwsException(
     const FunctionDecl *Func, const ExceptionInfo::Throwables &Caught,
     llvm::SmallSet<const FunctionDecl *, 32> &CallStack) {
-  if (CallStack.count(Func))
+  if (!Func || CallStack.count(Func) || (!CallStack.empty() && !canThrow(Func)))
     return ExceptionInfo::createNonThrowing();
 
   if (const Stmt *Body = Func->getBody()) {

clang-tools-extra/docs/ReleaseNotes.rst

@@ -275,7 +275,8 @@ Changes in existing checks
 
 - Improved :doc:`bugprone-exception-escape
   <clang-tidy/checks/bugprone/exception-escape>` to not emit warnings for
-  forward declarations of functions.
+  forward declarations of functions and additionally modified it to skip
+  ``noexcept`` functions during call stack analysis.
 
 - Fixed :doc:`bugprone-exception-escape<clang-tidy/checks/bugprone/exception-escape>`
   for coroutines where previously a warning would be emitted with coroutines

clang-tools-extra/test/clang-tidy/checkers/bugprone/exception-escape.cpp

@@ -152,7 +152,7 @@ void throw_catch_multi_ptr_4() noexcept {
 }
 
 // FIXME: In this case 'a' is convertible to the handler and should be caught
-// but in reality it's thrown. Note that clang doesn't report a warning for 
+// but in reality it's thrown. Note that clang doesn't report a warning for
 // this either.
 void throw_catch_multi_ptr_5() noexcept {
   try {
@@ -249,7 +249,7 @@ void throw_derived_catch_base_alias() noexcept {
 void throw_derived_catch_base_ptr_c() noexcept {
   try {
     derived d;
-    throw &d; 
+    throw &d;
   } catch(const base *) {
   }
 }
@@ -259,7 +259,7 @@ void throw_derived_catch_base_ptr() noexcept {
   try {
     derived d;
     const derived *p = &d;
-    throw p; 
+    throw p;
   } catch(base *) {
   }
 }
@@ -282,7 +282,7 @@ void throw_derived_catch_base_private() noexcept {
   // CHECK-MESSAGES: :[[@LINE-1]]:6: warning: an exception may be thrown in function 'throw_derived_catch_base_private' which should not throw exceptions
   try {
     B b;
-    throw b; 
+    throw b;
   } catch(A) {
   }
 }
@@ -291,7 +291,7 @@ void throw_derived_catch_base_private_ptr() noexcept {
   // CHECK-MESSAGES: :[[@LINE-1]]:6: warning: an exception may be thrown in function 'throw_derived_catch_base_private_ptr' which should not throw exceptions
   try {
     B b;
-    throw &b; 
+    throw &b;
   } catch(A *) {
   }
 }
@@ -300,7 +300,7 @@ void throw_derived_catch_base_protected() noexcept {
   // CHECK-MESSAGES: :[[@LINE-1]]:6: warning: an exception may be thrown in function 'throw_derived_catch_base_protected' which should not throw exceptions
   try {
     C c;
-    throw c; 
+    throw c;
   } catch(A) {
   }
 }
@@ -309,7 +309,7 @@ void throw_derived_catch_base_protected_ptr() noexcept {
   // CHECK-MESSAGES: :[[@LINE-1]]:6: warning: an exception may be thrown in function 'throw_derived_catch_base_protected_ptr' which should not throw exceptions
   try {
     C c;
-    throw &c; 
+    throw &c;
   } catch(A *) {
   }
 }
@@ -318,7 +318,7 @@ void throw_derived_catch_base_ambiguous() noexcept {
   // CHECK-MESSAGES: :[[@LINE-1]]:6: warning: an exception may be thrown in function 'throw_derived_catch_base_ambiguous' which should not throw exceptions
   try {
     E e;
-    throw e; 
+    throw e;
   } catch(A) {
   }
 }
@@ -327,7 +327,7 @@ void throw_derived_catch_base_ambiguous_ptr() noexcept {
   // CHECK-MESSAGES: :[[@LINE-1]]:6: warning: an exception may be thrown in function 'throw_derived_catch_base_ambiguous_ptr' which should not throw exceptions
   try {
     E e;
-    throw e; 
+    throw e;
   } catch(A) {
   }
 }
@@ -703,3 +703,22 @@ int main() {
   throw 1;
   return 0;
 }
+
+// The following function all incorrectly throw exceptions, *but* calling them
+// should not yield a warning because they are marked as noexcept.
+
+void test_basic_no_throw() noexcept { throw 42; }
+// CHECK-MESSAGES: :[[@LINE-1]]:6: warning: an exception may be thrown in function 'test_basic_no_throw' which should not throw exceptions
+
+void test_basic_throw() noexcept(false) { throw 42; }
+
+void only_calls_non_throwing() noexcept {
+  test_basic_no_throw();
+}
+
+void calls_non_and_throwing() noexcept {
+// CHECK-MESSAGES: :[[@LINE-1]]:6: warning: an exception may be thrown in function 'calls_non_and_throwing' which should not throw exceptions
+  test_basic_no_throw();
+  test_basic_throw();
+}
+