Re: [PATCH] Fix PR c++/111106: missing ; causes internal compiler error

[Jason Merrill]

On 5/30/24 07:31, Simon Martin wrote:
We currently fail upon the following because an assert in dependent_type_p
fails for f's parameter
=== cut here ===
consteval int id (int i) { return i; }
constexpr int
f (auto i) requires requires { id (i) } { return i; }
void g () { f (42); }
=== cut here ===

This patch fixes this by handling synthesized parameters for abbreviated
function templates in that assert.

I don't see why implicit template parameters should be handled 
differently from explicit ones here.

This seems more like an error-recovery issue, and I'd be open to adding 
|| seen_error() to that assert like in various others.

Successfully tested on x86_64-pc-linux-gnu.

        PR c++/111106

gcc/cp/ChangeLog:

        * pt.cc (dependent_type_p): Relax assert to handle synthesized template
        parameters when !processing_template_decl.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/consteval37.C: New test.

---
  gcc/cp/pt.cc                             |  6 +++++-
  gcc/testsuite/g++.dg/cpp2a/consteval37.C | 19 +++++++++++++++++++
  2 files changed, 24 insertions(+), 1 deletion(-)
  create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval37.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index dfce1b3c359..a50d5cfd5a2 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -28019,7 +28019,11 @@ dependent_type_p (tree type)
        /* If we are not processing a template, then nobody should be
         providing us with a dependent type.  */
        gcc_assert (type);
-      gcc_assert (TREE_CODE (type) != TEMPLATE_TYPE_PARM || is_auto (type));
+      gcc_assert (TREE_CODE (type) != TEMPLATE_TYPE_PARM || is_auto (type)
+                 || (/* Synthesized template parameter */
+                     DECL_TEMPLATE_PARM_P (TEMPLATE_TYPE_DECL (type)) &&
+                     (DECL_IMPLICIT_TEMPLATE_PARM_P
+                      (TEMPLATE_TYPE_DECL (type)))));
        return false;
      }
  
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval37.C b/gcc/testsuite/g++.dg/cpp2a/consteval37.C
new file mode 100644
index 00000000000..ea2641fc204
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval37.C
@@ -0,0 +1,19 @@
+// PR c++/111106
+// { dg-do compile { target c++20 } }
+
+consteval int id (int i) { return i; }
+
+constexpr int f (auto i) // { dg-line line_1 }
+  requires requires { id (i) } // { dg-error "expected|invalid use" }
+{
+  return i;
+}
+
+void g () {
+  f (42); // { dg-error "parameter 1" }
+}
+
+// { dg-error "constraints on a non-templated" {} { target *-*-* } line_1 }
+// { dg-error "has incomplete type" {} { target *-*-* } line_1 }
+// { dg-error "invalid type for" {} { target *-*-* } line_1 }
+// { dg-note "declared here" {} { target *-*-* } line_1 }

These errors are wrong, so should not be tested for;  only the syntax 
error about the missing semicolon should have a dg-error.  You can use 
dg-excess-errors to cover the rest.

Jason