[PATCH] c++: base-clause parsing and implicit 'this' [PR100362]

[PATCH] c++: base-clause parsing and implicit 'this' [PR100362]

[Patrick Palka]

My r11-6815 change to defer access checking when processing a
base-clause removed a pair of pushclass / popclass calls that seemed to
be unnecessary now that we'd also defer access checking while parsing
the base-clause.

But it turns out this makes a difference in the below testcase, where we
have a local class whose base clause implicitly uses the 'this' of the
enclosing class.  Before r11-6815, while parsing the base-clause of the
local class, maybe_resolve_dummy would fail to resolve the dummy 'this'
object because the current scope would be the local class.  Now, since
the current scope is the lambda, maybe_resolve_dummy succeeds and
returns the 'this' for the enclosing class Qux.  Later, during deferred
instantiation of the local class, we get confused trying to resolve the
access of 'a_' through this non-dummy 'this'.

So this patch just reinstates the calls to pushclass / popclass that
were removed in r11-6815.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
for trunk?

gcc/cp/ChangeLog:

	PR c++/100362
	* parser.c (cp_parser_class_head): Reinstate calls to pushclass
	and popclass during parsing of the base-clause that were
	removed in r11-6815.

gcc/testsuite/ChangeLog:

	PR c++/100362
	* g++.dg/cpp1y/lambda-generic-100362.C: New test.
---
 gcc/cp/parser.c                               |  8 +++++-
 .../g++.dg/cpp1y/lambda-generic-100362.C      | 25 +++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/lambda-generic-100362.C

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index e1b1617da68..28752611b34 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -25683,7 +25683,13 @@ cp_parser_class_head (cp_parser* parser,
      until the entire list has been seen, as per [class.access.general].  */
   push_deferring_access_checks (dk_deferred);
   if (cp_lexer_next_token_is (parser->lexer, CPP_COLON))
-    bases = cp_parser_base_clause (parser);
+    {
+      if (type)
+	pushclass (type);
+      bases = cp_parser_base_clause (parser);
+      if (type)
+	popclass ();
+    }
   else
     bases = NULL_TREE;
 
diff --git a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-100362.C b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-100362.C
new file mode 100644
index 00000000000..283c2c9477e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-100362.C
@@ -0,0 +1,25 @@
+// PR c++/100362
+// { dg-do compile { target c++14 } }
+
+template <class>
+struct Qux {
+  struct A { } a_;
+  A f();
+
+  void AsyncOp() {
+    [](auto) {
+      struct local : decltype(a_) {};
+      local ptr;
+    }(0);
+
+    [](auto) {
+      struct local : decltype(f()) {};
+      local ptr;
+    }(0);
+  }
+};
+
+void corge() {
+  Qux<int> qux;
+  qux.AsyncOp();
+}
-- 
2.31.1.442.g7e39198978

Re: [PATCH] c++: base-clause parsing and implicit 'this' [PR100362]

[Jason Merrill]

On 5/3/21 12:48 PM, Patrick Palka wrote:
> My r11-6815 change to defer access checking when processing a
> base-clause removed a pair of pushclass / popclass calls that seemed to
> be unnecessary now that we'd also defer access checking while parsing
> the base-clause.
> 
> But it turns out this makes a difference in the below testcase, where we
> have a local class whose base clause implicitly uses the 'this' of the
> enclosing class.  Before r11-6815, while parsing the base-clause of the
> local class, maybe_resolve_dummy would fail to resolve the dummy 'this'
> object because the current scope would be the local class.  Now, since
> the current scope is the lambda, maybe_resolve_dummy succeeds and
> returns the 'this' for the enclosing class Qux.  Later, during deferred
> instantiation of the local class, we get confused trying to resolve the
> access of 'a_' through this non-dummy 'this'.
> 
> So this patch just reinstates the calls to pushclass / popclass that
> were removed in r11-6815.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
> for trunk?

OK for trunk and 11.2.

> gcc/cp/ChangeLog:
> 
> 	PR c++/100362
> 	* parser.c (cp_parser_class_head): Reinstate calls to pushclass
> 	and popclass during parsing of the base-clause that were
> 	removed in r11-6815.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/100362
> 	* g++.dg/cpp1y/lambda-generic-100362.C: New test.
> ---
>   gcc/cp/parser.c                               |  8 +++++-
>   .../g++.dg/cpp1y/lambda-generic-100362.C      | 25 +++++++++++++++++++
>   2 files changed, 32 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp1y/lambda-generic-100362.C
> 
> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
> index e1b1617da68..28752611b34 100644
> --- a/gcc/cp/parser.c
> +++ b/gcc/cp/parser.c
> @@ -25683,7 +25683,13 @@ cp_parser_class_head (cp_parser* parser,
>        until the entire list has been seen, as per [class.access.general].  */
>     push_deferring_access_checks (dk_deferred);
>     if (cp_lexer_next_token_is (parser->lexer, CPP_COLON))
> -    bases = cp_parser_base_clause (parser);
> +    {
> +      if (type)
> +	pushclass (type);
> +      bases = cp_parser_base_clause (parser);
> +      if (type)
> +	popclass ();
> +    }
>     else
>       bases = NULL_TREE;
>   
> diff --git a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-100362.C b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-100362.C
> new file mode 100644
> index 00000000000..283c2c9477e
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-100362.C
> @@ -0,0 +1,25 @@
> +// PR c++/100362
> +// { dg-do compile { target c++14 } }
> +
> +template <class>
> +struct Qux {
> +  struct A { } a_;
> +  A f();
> +
> +  void AsyncOp() {
> +    [](auto) {
> +      struct local : decltype(a_) {};
> +      local ptr;
> +    }(0);
> +
> +    [](auto) {
> +      struct local : decltype(f()) {};
> +      local ptr;
> +    }(0);
> +  }
> +};
> +
> +void corge() {
> +  Qux<int> qux;
> +  qux.AsyncOp();
> +}
>