[PATCH] c++: Fix ICE-on-invalid with lambda template [PR94507]

[Jason Merrill]

On 4/6/20 9:05 PM, Marek Polacek wrote:
> While reducing something else I noticed that we ICE on the following
> invalid code.  In tsubst_lambda_expr, tsubst_template_decl has already
> reported an error and returned the error_mark_node, so make sure we
> don't ICE on that.  I'm using a goto here because we still have to
> do finish_struct because it does popclass ().
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> 
> 	PR c++/94507 - ICE-on-invalid with lambda template.
> 	* pt.c (tsubst_lambda_expr): Cope when tsubst_template_decl returns
> 	error_mark_node.
> 
> 	* g++.dg/cpp2a/lambda-generic7.C: New test.
> ---
>   gcc/cp/pt.c                                  |  6 ++++++
>   gcc/testsuite/g++.dg/cpp2a/lambda-generic7.C | 10 ++++++++++
>   2 files changed, 16 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-generic7.C
> 
> diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> index 6122227c22f..f804ba18692 100644
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -18876,6 +18876,11 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
>         if (oldtmpl)
>   	{
>   	  tmpl = tsubst_template_decl (oldtmpl, args, complain, fntype);
> +	  if (tmpl == error_mark_node)
> +	    {
> +	      r = error_mark_node;
> +	      goto out;
> +	    }
>   	  fn = DECL_TEMPLATE_RESULT (tmpl);
>   	  finish_member_declaration (tmpl);
>   	}

Perhaps we also want an early exit if the tsubst_function_decl in the 
else clause returns error_mark_node?

> @@ -18948,6 +18953,7 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
>         maybe_add_lambda_conv_op (type);
>       }
>   
> +out:
>     finish_struct (type, /*attr*/NULL_TREE);
>   
>     insert_pending_capture_proxies ();
> diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-generic7.C b/gcc/testsuite/g++.dg/cpp2a/lambda-generic7.C
> new file mode 100644
> index 00000000000..bedba683671
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/lambda-generic7.C
> @@ -0,0 +1,10 @@
> +// PR c++/94507 - ICE-on-invalid with lambda template.
> +// { dg-do compile { target c++2a } }
> +
> +struct S { };
> +
> +template<typename T, typename U>
> +auto foo(T, U)
> +{
> +  [] <> () { foo (S{}, S{}); }; // { dg-error "expected" }
> +}
> 
> base-commit: 130f703da0c0d7b785d394b17df884379b4aadd9
>