On 11/14/23 11:10, Patrick Palka wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?
-- >8 --
For decltype((x)) within a lambda where x is not captured, we dubiously
require that the lambda has a capture default, unlike for decltype(x).
This patch fixes this inconsistency; I couldn't find a justification for
it in the standard.
The relevant passage seems to be
https://eel.is/c++draft/expr.prim#id.unqual-3
"If naming the entity from outside of an unevaluated operand within S
would refer to an entity captured by copy in some intervening
lambda-expression, then let E be the innermost such lambda-expression.
If there is such a lambda-expression and if P is in E's function
parameter scope but not its parameter-declaration-clause, then the type
of the expression is the type of a class member access expression
([expr.ref]) naming the non-static data member that would be declared
for such a capture in the object parameter ([dcl.fct]) of the function
call operator of E."
In this case I guess there is no such lambda-expression because naming x
won't refer to a capture by copy if the lambda doesn't capture anything,
so we ignore the lambda.
Maybe refer to that in a comment? OK with that change.
I'm surprised that it refers specifically to capture by copy, but I
guess a capture by reference should have the same decltype as the
captured variable?
Jason
PR c++/83167
gcc/cp/ChangeLog:
* semantics.cc (finish_decltype_type): If capture_decltype
returns NULL_TREE, fall back to the ordinary code path.
(capture_decltype): Return NULL_TREE if the lambda has no
capture-default.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/lambda/lambda-decltype4.C: New test.
---
gcc/cp/semantics.cc | 6 +++---
.../g++.dg/cpp0x/lambda/lambda-decltype4.C | 15 +++++++++++++++
2 files changed, 18 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-decltype4.C
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 8090c71809f..6fdd6c45972 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -11732,7 +11732,8 @@ finish_decltype_type (tree expr, bool
id_expression_or_member_access_p,
/* If the expression is just "this", we want the
cv-unqualified pointer for the "this" type. */
type = TYPE_MAIN_VARIANT (TREE_TYPE (expr));
- else
+
+ if (!type)
{
/* Otherwise, where T is the type of e, if e is an lvalue,
decltype(e) is defined as T&; if an xvalue, T&&; otherwise, T. */
@@ -12639,8 +12640,7 @@ capture_decltype (tree decl)
switch (LAMBDA_EXPR_DEFAULT_CAPTURE_MODE (lam))
{
case CPLD_NONE:
- error ("%qD is not captured", decl);
- return error_mark_node;
+ return NULL_TREE;
case CPLD_COPY:
type = TREE_TYPE (decl);
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-decltype4.C
b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-decltype4.C
new file mode 100644
index 00000000000..0062d7b8672
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-decltype4.C
@@ -0,0 +1,15 @@
+// PR c++/83167
+// { dg-do compile { target c++11 } }
+
+int main() {
+ int x;
+ const int y = 42;
+
+ [] {
+ using ty1 = decltype((x));
+ using ty1 = int&;
+
+ using ty2 = decltype((y));
+ using ty2 = const int&;
+ };
+}
