Refactor the way we handle diagnosing unused expression results.
Rather than sprinkle calls to DiagnoseUnusedExprResult() around in places where we want diagnostics, we now diagnose unused expression statements and full expressions in a more generic way when acting on the final expression statement. This results in more appropriate diagnostics for [[nodiscard]] where we were previously lacking them, such as when the body of a for loop is not a compound statement.
This patch fixes PR39837.
llvm-svn: 350404
diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
index 313793c..2974e6a 100644
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -439,7 +439,7 @@
// Otherwise, eat the semicolon.
ExpectAndConsumeSemi(diag::err_expected_semi_after_expr);
- return Actions.ActOnExprStmt(Expr);
+ return Actions.ActOnExprStmt(Expr, isExprValueDiscarded());
}
/// ParseSEHTryBlockCommon
@@ -958,6 +958,16 @@
return true;
}
+bool Parser::isExprValueDiscarded() {
+ if (Actions.isCurCompoundStmtAStmtExpr()) {
+ // Look to see if the next two tokens close the statement expression;
+ // if so, this expression statement is the last statement in a
+ // statment expression.
+ return Tok.isNot(tok::r_brace) || NextToken().isNot(tok::r_paren);
+ }
+ return true;
+}
+
/// ParseCompoundStatementBody - Parse a sequence of statements and invoke the
/// ActOnCompoundStmt action. This expects the '{' to be the current token, and
/// consume the '}' at the end of the block. It does not manipulate the scope
@@ -1062,7 +1072,7 @@
// Eat the semicolon at the end of stmt and convert the expr into a
// statement.
ExpectAndConsumeSemi(diag::err_expected_semi_after_expr);
- R = Actions.ActOnExprStmt(Res);
+ R = Actions.ActOnExprStmt(Res, isExprValueDiscarded());
}
}
@@ -1698,8 +1708,16 @@
if (!Value.isInvalid()) {
if (ForEach)
FirstPart = Actions.ActOnForEachLValueExpr(Value.get());
- else
- FirstPart = Actions.ActOnExprStmt(Value);
+ else {
+ // We already know this is not an init-statement within a for loop, so
+ // if we are parsing a C++11 range-based for loop, we should treat this
+ // expression statement as being a discarded value expression because
+ // we will err below. This way we do not warn on an unused expression
+ // that was an error in the first place, like with: for (expr : expr);
+ bool IsRangeBasedFor =
+ getLangOpts().CPlusPlus11 && !ForEach && Tok.is(tok::colon);
+ FirstPart = Actions.ActOnExprStmt(Value, !IsRangeBasedFor);
+ }
}
if (Tok.is(tok::semi)) {