modocache created this revision.
modocache added reviewers: GorNishanov, tks2103, rsmith.
Herald added subscribers: jdoerfert, EricWF.
Herald added a project: clang.
As reported in https://bugs.llvm.org/show_bug.cgi?id=40978, it's an
error to use the `co_yield` or `co_await` keywords outside of a valid
"suspension context" as defined by [expr.await]p2 of
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/n4775.pdf.
Whether or not the current scope was in a function-try-block's
(https://en.cppreference.com/w/cpp/language/function-try-block) handler
could be determined using scope flag `Scope::FnTryCatchScope`. No
such flag existed for a simple C++ catch statement, so this commit adds
one.
Repository:
rC Clang
https://reviews.llvm.org/D59076
Files:
include/clang/Basic/DiagnosticSemaKinds.td
include/clang/Sema/Scope.h
lib/Parse/ParseStmt.cpp
lib/Sema/SemaCoroutine.cpp
test/SemaCXX/coroutines.cpp
Index: test/SemaCXX/coroutines.cpp
===================================================================
--- test/SemaCXX/coroutines.cpp
+++ test/SemaCXX/coroutines.cpp
@@ -328,6 +328,27 @@
// not allowed. A user may not understand that this is "outside a function."
void default_argument(int arg = co_await 0) {} // expected-error {{'co_await' cannot be used outside a function}}
+void await_in_catch_coroutine() {
+ try {
+ } catch (...) {
+ co_await a; // expected-error {{'co_await' cannot be used in the handler of a try block}}
+ }
+}
+
+void yield_in_catch_coroutine() {
+ try {
+ } catch (...) {
+ co_yield a; // expected-error {{'co_yield' cannot be used in the handler of a try block}}
+ }
+}
+
+void return_in_catch_coroutine() {
+ try {
+ } catch (...) {
+ co_return 123; // OK
+ }
+}
+
constexpr auto constexpr_deduced_return_coroutine() {
co_yield 0; // expected-error {{'co_yield' cannot be used in a constexpr function}}
// expected-error@-1 {{'co_yield' cannot be used in a function with a deduced return type}}
Index: lib/Sema/SemaCoroutine.cpp
===================================================================
--- lib/Sema/SemaCoroutine.cpp
+++ lib/Sema/SemaCoroutine.cpp
@@ -185,21 +185,8 @@
static bool isValidCoroutineContext(Sema &S, SourceLocation Loc,
StringRef Keyword) {
- // 'co_await' and 'co_yield' are not permitted in unevaluated operands,
- // such as subexpressions of \c sizeof.
- //
- // [expr.await]p2, emphasis added: "An await-expression shall appear only in
- // a *potentially evaluated* expression within the compound-statement of a
- // function-body outside of a handler [...] A context within a function where
- // an await-expression can appear is called a suspension context of the
- // function." And per [expr.yield]p1: "A yield-expression shall appear only
- // within a suspension context of a function."
- if (S.isUnevaluatedContext()) {
- S.Diag(Loc, diag::err_coroutine_unevaluated_context) << Keyword;
- return false;
- }
-
- // Per [expr.await]p2, any other usage must be within a function.
+ // [expr.await]p2 dictates that 'co_await' and 'co_yield' must be used within
+ // a function body.
// FIXME: This also covers [expr.await]p2: "An await-expression shall not
// appear in a default argument." But the diagnostic QoI here could be
// improved to inform the user that default arguments specifically are not
@@ -668,8 +655,34 @@
return true;
}
+// [expr.await]p2, emphasis added: "An await-expression shall appear only in
+// a *potentially evaluated* expression within the compound-statement of a
+// function-body *outside of a handler* [...] A context within a function
+// where an await-expression can appear is called a suspension context of the
+// function."
+static bool isValidSuspensionContext(Sema &S, SourceLocation Loc,
+ StringRef Keyword,
+ bool IsImplicit = false) {
+ // First emphasis of [expr.await]p2: must be a potentially evaluated context.
+ // That is, 'co_await' and 'co_yield' cannot appear in subexpressions of
+ // \c sizeof.
+ if (S.isUnevaluatedContext()) {
+ S.Diag(Loc, diag::err_coroutine_unevaluated_context) << Keyword;
+ return false;
+ }
+
+ // Second emphasis of [expr.await]p2: must be outside of an exception handler.
+ if (S.getCurScope()->getFlags() & Scope::CatchScope) {
+ S.Diag(Loc, diag::err_coroutine_within_handler) << Keyword;
+ return false;
+ }
+
+ return true;
+}
+
ExprResult Sema::ActOnCoawaitExpr(Scope *S, SourceLocation Loc, Expr *E) {
- if (!ActOnCoroutineBodyStart(S, Loc, "co_await")) {
+ if (!ActOnCoroutineBodyStart(S, Loc, "co_await") ||
+ !isValidSuspensionContext(*this, Loc, "co_await")) {
CorrectDelayedTyposInExpr(E);
return ExprError();
}
@@ -689,7 +702,7 @@
ExprResult Sema::BuildUnresolvedCoawaitExpr(SourceLocation Loc, Expr *E,
UnresolvedLookupExpr *Lookup) {
auto *FSI = checkCoroutineContext(*this, Loc, "co_await");
- if (!FSI)
+ if (!FSI || !isValidSuspensionContext(*this, Loc, "co_await"))
return ExprError();
if (E->getType()->isPlaceholderType()) {
@@ -766,7 +779,8 @@
}
ExprResult Sema::ActOnCoyieldExpr(Scope *S, SourceLocation Loc, Expr *E) {
- if (!ActOnCoroutineBodyStart(S, Loc, "co_yield")) {
+ if (!ActOnCoroutineBodyStart(S, Loc, "co_yield") ||
+ !isValidSuspensionContext(*this, Loc, "co_yield")) {
CorrectDelayedTyposInExpr(E);
return ExprError();
}
Index: lib/Parse/ParseStmt.cpp
===================================================================
--- lib/Parse/ParseStmt.cpp
+++ lib/Parse/ParseStmt.cpp
@@ -2260,8 +2260,10 @@
// C++ 3.3.2p3:
// The name in a catch exception-declaration is local to the handler and
// shall not be redeclared in the outermost block of the handler.
- ParseScope CatchScope(this, Scope::DeclScope | Scope::ControlScope |
- (FnCatch ? Scope::FnTryCatchScope : 0));
+ unsigned ScopeFlags = Scope::DeclScope | Scope::ControlScope |
+ Scope::CatchScope |
+ (FnCatch ? Scope::FnTryCatchScope : 0);
+ ParseScope CatchScope(this, ScopeFlags);
// exception-declaration is equivalent to '...' or a parameter-declaration
// without default arguments.
@@ -2290,7 +2292,7 @@
return StmtError(Diag(Tok, diag::err_expected) << tok::l_brace);
// FIXME: Possible draft standard bug: attribute-specifier should be allowed?
- StmtResult Block(ParseCompoundStatement());
+ StmtResult Block(ParseCompoundStatement(/*isStmtExpr=*/false, ScopeFlags));
if (Block.isInvalid())
return Block;
Index: include/clang/Sema/Scope.h
===================================================================
--- include/clang/Sema/Scope.h
+++ include/clang/Sema/Scope.h
@@ -131,6 +131,9 @@
/// We are between inheritance colon and the real class/struct definition scope.
ClassInheritanceScope = 0x800000,
+
+ /// This is the scope of a C++ catch statement.
+ CatchScope = 0x1000000,
};
private:
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -9244,6 +9244,8 @@
"Objective-C methods as coroutines are not yet supported">;
def err_coroutine_unevaluated_context : Error<
"'%0' cannot be used in an unevaluated context">;
+def err_coroutine_within_handler : Error<
+ "'%0' cannot be used in the handler of a try block">;
def err_coroutine_outside_function : Error<
"'%0' cannot be used outside a function">;
def err_coroutine_invalid_func_context : Error<
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