On 4/3/23 12:28, Patrick Palka wrote:
On Wed, 29 Mar 2023, Jason Merrill wrote:
On 3/28/23 13:37, Patrick Palka wrote:
Now that we resolve non-dependent variable template-ids ahead of time,
cp_finish_decl needs to handle a new invalid situation: we can end up
trying to instantiate a variable template with deduced return type
before we fully parsed (and attached) its initializer.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this OK for
trunK?
PR c++/109300
gcc/cp/ChangeLog:
* decl.cc (cp_finish_decl): Diagnose ordinary auto deduction
with no initializer instead of asserting.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/var-templ79.C: New test.
---
gcc/cp/decl.cc | 15 ++++++++++++++-
gcc/testsuite/g++.dg/cpp1y/var-templ79.C | 5 +++++
2 files changed, 19 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/var-templ79.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 20b980f68c8..2c91693b99d 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -8276,7 +8276,20 @@ cp_finish_decl (tree decl, tree init, bool
init_const_expr_p,
return;
}
- gcc_assert (CLASS_PLACEHOLDER_TEMPLATE (auto_node));
+ if (CLASS_PLACEHOLDER_TEMPLATE (auto_node))
+ /* Class deduction with no initializer is OK. */;
+ else
+ {
+ /* Ordinary auto deduction without an initializer, a situation
+ which grokdeclarator already catches and rejects for the most
+ part. But we can still get here if we're instantiating a
+ variable template before we've fully parsed (and attached)
its
+ initializer, e.g. template<class> auto x = x<int>; */
In the case of recursively dependent instantiation I'd hope to have an
error_mark_node initializer, rather than none?
Do you mean setting the initializer to error_mark_node after the fact, e.g.
@@ -8288,7 +8297,7 @@ cp_finish_decl (tree decl, tree init, bool
init_const_expr_p,
error_at (DECL_SOURCE_LOCATION (decl),
"declaration of %q#D has no initializer", decl);
TREE_TYPE (decl) = error_mark_node;
- return;
+ init = error_mark_node;
}
}
d_init = init;
or before the fact, i.e. setting DECL_INITIAL to error_mark_node as a
sentinel value for detecting recursion before we begin parsing a variable
initializer? The former should work I suppose, but the latter is
problematic because we also call cp_finish_decl with init=error_mark_node
when the initializer is generally invalid, so by overloading the meaning
of error_mark_node here and checking for it from cp_finish_decl we would
end up emitting a bogus extra diagnostic in a bunch of cases e.g.
g++.dg/pr53055.C:
int i = p ->* p ; // invalid initializer
I guess we would need to use a different sentinel value for detecting
recursion, or expose and inspect the 'lambda_scope' stack which already
keeps track of whether we're in the middle of a variable initializer...
Dunno if it's worth it just for sake of a better diagnostic for this
corner case, I notice e.g. Clang doesn't give a great diagnostic either:
src/gcc/testsuite/g++.dg/cpp1y/var-templ79.C:5:6: error: declaration of
variable 'x' with deduced type 'auto' requires an initializer
auto x = x<int>; // { dg-error "" }
^
Yeah, let's just go with your patch, thanks.
+ error_at (DECL_SOURCE_LOCATION (decl),
+ "declaration of %q#D has no initializer", decl);
+ TREE_TYPE (decl) = error_mark_node;
+ return;
+ }
}
d_init = init;
if (d_init)
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ79.C
b/gcc/testsuite/g++.dg/cpp1y/var-templ79.C
new file mode 100644
index 00000000000..3c0d276153a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ79.C
@@ -0,0 +1,5 @@
+// PR c++/109300
+// { dg-do compile { target c++14 } }
+
+template<class>
+auto x = x<int>; // { dg-error "" }
