Re: [PATCH v8 1/4] c++: P0847R7 (deducing this) - prerequisite changes. [PR102609]

[Jason Merrill <jason@redhat.com>]

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On 1/9/24 15:58, Jason Merrill wrote:
> On 1/6/24 19:00, waffl3x wrote:
>> Bootstrapped and tested on x86_64-linux with no regressions.
>>
>> I'm considering this finished, I have CWG2586 working but I have not
>> included it in this version of the patch. I was not happy with the
>> amount of work I had done on it. I will try to get it finished before
>> we get cut off, and I'm pretty sure I can. I just don't want to risk
>> missing the boat for the whole patch just for that.
>>
>> There aren't too many changes from v7, it's mostly just cleaned up.
>> There are a few though, so do take a look, if there's anything severe I
>> can rush to fix it if necessary.
>>
>> That's all, hopefully all is good, fingers crossed.
> 
> Great.  Given where we are in the release cycle, I'm thinking to put 
> these with only minimal changes and then do any further adjustments 
> afterward.
> 
> For this first one, I needed to fix the commit message to wrap at 75 
> columns so that it fits in 80 columns with the initial padding added by 
> 'git log'.  I also needed to adjust the ChangeLog entry to please git 
> gcc-verify.  And I changed the credit note to a Co-authored-by.
> 
> The other commit messages only needed wrapping.

I just pushed your patches along with these two follow-ons:

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From 5a6d3b1737843aa64d83ffc5d639fa0afa5d8318 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Tue, 9 Jan 2024 16:00:52 -0500
Subject: [PATCH 1/2] c++: explicit object cleanups
To: gcc-patches@gcc.gnu.org

The FIXME in xobj_iobj_parameters_correspond was due to expecting
TYPE_MAIN_VARIANT to be the same for all equivalent types, which is not the
case.  And I adjusted some comments that I disagree with; the iobj parameter
adjustment only applies to overload resolution, we can handle that in
cand_parms_match (and I have WIP for that).

gcc/cp/ChangeLog:

	* call.cc (build_over_call): Refactor handle_arg lambda.
	* class.cc (xobj_iobj_parameters_correspond): Fix FIXME.
	* method.cc (defaulted_late_check): Adjust comments.
---
 gcc/cp/call.cc   | 24 ++++++++++++------------
 gcc/cp/class.cc  | 40 ++++++++++++----------------------------
 gcc/cp/method.cc |  7 +------
 3 files changed, 25 insertions(+), 46 deletions(-)

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index dca8e5090e2..7d3d67600c8 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -10187,11 +10187,11 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
       parm = TREE_CHAIN (parm);
     }
 
-  auto handle_arg = [fn, flags, complain](tree type,
-					  tree arg,
-					  int const param_index,
-					  conversion *conv,
-					  bool const conversion_warning)
+  auto handle_arg = [fn, flags](tree type,
+				tree arg,
+				int const param_index,
+				conversion *conv,
+				tsubst_flags_t const arg_complain)
     {
       /* Set user_conv_p on the argument conversions, so rvalue/base handling
 	 knows not to allow any more UDCs.  This needs to happen after we
@@ -10199,9 +10199,6 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
       if (flags & LOOKUP_NO_CONVERSION)
 	conv->user_conv_p = true;
 
-      tsubst_flags_t const arg_complain
-	= conversion_warning ? complain : complain & ~tf_warning;
-
       if (arg_complain & tf_warning)
 	maybe_warn_pessimizing_move (arg, type, /*return_p=*/false);
 
@@ -10214,13 +10211,12 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
   if (DECL_XOBJ_MEMBER_FUNCTION_P (fn))
     {
       gcc_assert (cand->num_convs > 0);
-      static constexpr bool conversion_warning = true;
       tree object_arg = consume_object_arg ();
       val = handle_arg (TREE_VALUE (parm),
 			object_arg,
 			param_index++,
 			convs[conv_index++],
-			conversion_warning);
+			complain);
 
       if (val == error_mark_node)
 	return error_mark_node;
@@ -10260,11 +10256,14 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 					&& cand->template_decl
 					&& !cand->explicit_targs);
 
+      tsubst_flags_t const arg_complain
+	= conversion_warning ? complain : complain & ~tf_warning;
+
       val = handle_arg (TREE_VALUE (parm),
 			current_arg,
 			param_index,
 			convs[conv_index],
-			conversion_warning);
+			arg_complain);
 
       if (val == error_mark_node)
 	return error_mark_node;
@@ -10273,7 +10272,8 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
     }
 
   /* Default arguments */
-  for (; parm && parm != void_list_node; parm = TREE_CHAIN (parm), param_index++)
+  for (; parm && parm != void_list_node;
+       parm = TREE_CHAIN (parm), param_index++)
     {
       if (TREE_VALUE (parm) == error_mark_node)
 	return error_mark_node;
diff --git a/gcc/cp/class.cc b/gcc/cp/class.cc
index f3cfa9f0f23..e5e609badf3 100644
--- a/gcc/cp/class.cc
+++ b/gcc/cp/class.cc
@@ -1020,9 +1020,12 @@ modify_vtable_entry (tree t,
 
 \f
 /* Check if the object parameters of an xobj and iobj member function
-   correspond. This function assumes that the iobj parameter has been correctly
-   adjusted when the function is introduced by a using declaration per
-   [over.match.funcs.general.4].  */
+   correspond.  This function assumes that the iobj parameter has been
+   correctly adjusted when the function is introduced by a using declaration
+   per [over.match.funcs.general.4].
+
+   ??? But it isn't, that's only considered at overload resolution time.
+   cand_parms_match will probably need to check cand->conversion_path.  */
 
 bool
 xobj_iobj_parameters_correspond (tree fn1, tree fn2)
@@ -1112,29 +1115,10 @@ xobj_iobj_parameters_correspond (tree fn1, tree fn2)
      handles xobj parameters of pointer type, we don't have to explicitly
      check for that case.  */
 
-  /* FIXME:
-
-     template<typename>
-     struct S;
-
-     template<typename>
-     struct B {
-       int f(this S<void>&) requires true { return 5; }
-     };
-
-     template<typename>
-     struct S : B<void> {
-       using B<void>::f;
-       int f() { return 10; }
-     };
-
-     This case is broken, the incomplete type seems to screw with things.
-     I'm not sure how to fix that so I'm just noting the issue here, I have a
-     feeling it's trivial to do if you know how.  */
-
-  if (TYPE_MAIN_VARIANT (iobj_param_type)
-      != TYPE_MAIN_VARIANT (non_reference (xobj_param)))
+  if (!same_type_ignoring_top_level_qualifiers_p
+      (iobj_param_type, non_reference (xobj_param)))
     return false;
+
   /* We don't get to bail yet even if we have a by-value xobj parameter,
      a by-value xobj parameter can correspond to an iobj parameter provided the
      iobj member function is not declared with a reference qualifier.
@@ -8976,9 +8960,9 @@ resolve_address_of_overloaded_function (tree target_type,
 	 documentation for -fms-extensions states it's purpose is to support
 	 the use of microsoft headers.  Until otherwise demonstrated, we should
 	 assume xobj member functions are not used in this manner in microsoft
-	 headers and indiscriminately forbid the incorrect syntax instead of
-	 supporting it for non-legacy uses.  This should hopefully encourage
-	 conformance going forward.
+	 headers and forbid the incorrect syntax instead of supporting it for
+	 non-legacy uses.  This should hopefully encourage conformance going
+	 forward.
 	 This comment is referred to in typeck.cc:cp_build_addr_expr_1.  */
       if (DECL_IOBJ_MEMBER_FUNCTION_P (fn) && flag_ms_extensions)
 	/* Early escape.  */;
diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index da6a08a0304..6a9f03eb8f3 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -3400,8 +3400,7 @@ defaulted_late_check (tree fn)
 	    || TYPE_REF_IS_RVALUE (fn_obj_ref_type))
 	  return false;
 	/* If implicit_fn's object parameter is not a pointer, something is not
-	   right.  (Or we have finally changed the type of the iobj parameter
-	   in iobj member functions.)  */
+	   right.  */
 	gcc_assert (TYPE_PTR_P (TREE_VALUE (implicit_fn_parms)));
 	/* Strip the reference/pointer off each object parameter before
 	   comparing them.  */
@@ -3422,10 +3421,6 @@ defaulted_late_check (tree fn)
     {
       error ("defaulted declaration %q+D does not match the "
 	     "expected signature", fn);
-      /* FIXME: If the user is defaulting an xobj member function we should
-	 emit an xobj member function for a signature.  When we do this, maybe
-	 we can just synthesize implicit_fn as an xobj member function and
-	 avoid the dance in compare_fn_parms.  */
       inform (DECL_SOURCE_LOCATION (fn),
 	      "expected signature: %qD", implicit_fn);
     }
-- 
2.39.3


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From ae3003b20d3e3ab6e50a6d4f2173e10ad9025135 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Mon, 8 Jan 2024 17:09:54 -0500
Subject: [PATCH 2/2] c++: adjust accessor fixits for explicit object parm
To: gcc-patches@gcc.gnu.org

In a couple of places in the xobj patch I noticed that is_this_parameter
probably wanted to change to is_object_parameter; this implements that and
does the additional adjustments needed to make the accessor fixits handle
xobj parms.

gcc/cp/ChangeLog:

	* semantics.cc (is_object_parameter): New.
	* cp-tree.h (is_object_parameter): Declare.
	* call.cc (maybe_warn_class_memaccess): Use it.
	* search.cc (field_access_p): Use it.
	(class_of_object_parm): New.
	(field_accessor_p): Adjust for explicit object parms.

gcc/testsuite/ChangeLog:

	* g++.dg/torture/accessor-fixits-9-xobj.C: New test.
---
 gcc/cp/cp-tree.h                              |   1 +
 gcc/cp/call.cc                                |   3 +-
 gcc/cp/search.cc                              |  19 ++-
 gcc/cp/semantics.cc                           |  14 +++
 .../g++.dg/torture/accessor-fixits-9-xobj.C   | 119 ++++++++++++++++++
 5 files changed, 149 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/torture/accessor-fixits-9-xobj.C

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index dbc71776be3..f3f265a3db8 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7784,6 +7784,7 @@ extern void finish_handler_parms		(tree, tree);
 extern void finish_handler			(tree);
 extern void finish_cleanup			(tree, tree);
 extern bool is_this_parameter                   (tree);
+extern bool is_object_parameter                 (tree);
 
 enum {
   BCS_NORMAL = 0,
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 7d3d67600c8..191664ee227 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -10815,8 +10815,7 @@ maybe_warn_class_memaccess (location_t loc, tree fndecl,
      be more permissive.  */
   if (current_function_decl
       && DECL_OBJECT_MEMBER_FUNCTION_P (current_function_decl)
-      /* ??? is_object_parameter?  */
-      && is_this_parameter (tree_strip_nop_conversions (dest)))
+      && is_object_parameter (tree_strip_nop_conversions (dest)))
     {
       tree ctx = DECL_CONTEXT (current_function_decl);
       bool special = same_type_ignoring_top_level_qualifiers_p (ctx, desttype);
diff --git a/gcc/cp/search.cc b/gcc/cp/search.cc
index dc76714351f..2b4ed5d024e 100644
--- a/gcc/cp/search.cc
+++ b/gcc/cp/search.cc
@@ -1737,8 +1737,7 @@ field_access_p (tree component_ref, tree field_decl, tree field_type)
     return false;
 
   tree ptr = STRIP_NOPS (TREE_OPERAND (indirect_ref, 0));
-  /* ??? is_object_parameter?  */
-  if (!is_this_parameter (ptr))
+  if (!is_object_parameter (ptr))
     return false;
 
   /* Must access the correct field.  */
@@ -1818,6 +1817,17 @@ reference_accessor_p (tree init_expr, tree field_decl, tree field_type,
   return true;
 }
 
+/* Return the class of the `this' or explicit object parameter of FN.  */
+
+static tree
+class_of_object_parm (const_tree fn)
+{
+  tree fntype = TREE_TYPE (fn);
+  if (DECL_XOBJ_MEMBER_FUNCTION_P (fn))
+    return non_reference (TREE_VALUE (TYPE_ARG_TYPES (fntype)));
+  return class_of_this_parm (fntype);
+}
+
 /* Return true if FN is an accessor method for FIELD_DECL.
    i.e. a method of the form { return FIELD; }, with no
    conversions.
@@ -1835,15 +1845,14 @@ field_accessor_p (tree fn, tree field_decl, bool const_p)
   if (TREE_CODE (field_decl) != FIELD_DECL)
     return false;
 
-  tree fntype = TREE_TYPE (fn);
-  if (TREE_CODE (fntype) != METHOD_TYPE)
+  if (!DECL_OBJECT_MEMBER_FUNCTION_P (fn))
     return false;
 
   /* If the field is accessed via a const "this" argument, verify
      that the "this" parameter is const.  */
   if (const_p)
     {
-      tree this_class = class_of_this_parm (fntype);
+      tree this_class = class_of_object_parm (fn);
       if (!TYPE_READONLY (this_class))
 	return false;
     }
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 86e1adf1e71..3299e270446 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12832,6 +12832,20 @@ is_this_parameter (tree t)
   return true;
 }
 
+/* As above, or a C++23 explicit object parameter.  */
+
+bool
+is_object_parameter (tree t)
+{
+  if (is_this_parameter (t))
+    return true;
+  if (TREE_CODE (t) != PARM_DECL)
+    return false;
+  tree ctx = DECL_CONTEXT (t);
+  return (ctx && DECL_XOBJ_MEMBER_FUNCTION_P (ctx)
+	  && t == DECL_ARGUMENTS (ctx));
+}
+
 /* Insert the deduced return type for an auto function.  */
 
 void
diff --git a/gcc/testsuite/g++.dg/torture/accessor-fixits-9-xobj.C b/gcc/testsuite/g++.dg/torture/accessor-fixits-9-xobj.C
new file mode 100644
index 00000000000..89be978ae8e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/accessor-fixits-9-xobj.C
@@ -0,0 +1,119 @@
+// PR c++/84993
+// { dg-options "-fdiagnostics-show-caret -std=c++23" }
+
+/* Misspelling (by omitting a leading "m_") of a private member for which
+   there's a public accessor.
+
+   We expect a fix-it hint suggesting the accessor.  */
+
+class t1
+{
+public:
+  int get_ratio (this const t1& x) { return x.m_ratio; }
+
+private:
+  int m_ratio;
+};
+
+int test (t1 *ptr_1)
+{
+  return ptr_1->ratio; // { dg-error "'class t1' has no member named 'ratio'; did you mean 'int t1::m_ratio'\\? \\(accessible via 'int t1::get_ratio\\(this const t1&\\)'\\)" }
+  /* { dg-begin-multiline-output "" }
+   return ptr_1->ratio;
+                 ^~~~~
+                 get_ratio()
+     { dg-end-multiline-output "" } */
+}
+
+
+/* Misspelling of a private member for which there's a public accessor.
+
+   We expect a fix-it hint suggesting the accessor.  */
+
+class t2
+{
+public:
+  int get_color (this const t2& x) { return x.m_color; }
+
+private:
+  int m_color;
+};
+
+int test (t2 *ptr_2)
+{
+  return ptr_2->m_colour; // { dg-error "'class t2' has no member named 'm_colour'; did you mean 'int t2::m_color'\\? \\(accessible via 'int t2::get_color\\(this const t2&\\)'\\)" }
+  /* { dg-begin-multiline-output "" }
+   return ptr_2->m_colour;
+                 ^~~~~~~~
+                 get_color()
+     { dg-end-multiline-output "" } */
+}
+
+
+/* Misspelling of a private member via a subclass pointer, for which there's
+   a public accessor in the base class.
+
+   We expect a fix-it hint suggesting the accessor.  */
+
+class t3 : public t2 {};
+
+int test (t3 *ptr_3)
+{
+  return ptr_3->m_colour; // { dg-error "'class t3' has no member named 'm_colour'; did you mean 'int t2::m_color'\\? \\(accessible via 'int t2::get_color\\(this const t2&\\)'\\)" }
+  /* { dg-begin-multiline-output "" }
+   return ptr_3->m_colour;
+                 ^~~~~~~~
+                 get_color()
+     { dg-end-multiline-output "" } */
+}
+
+
+/* Misspelling of a protected member, for which there's isn't a public
+   accessor.
+
+   We expect no fix-it hint; instead a message identifying where the
+   data member was declared.  */
+
+class t4
+{
+protected:
+  int m_color; // { dg-message "declared protected here" }
+};
+
+int test (t4 *ptr_4)
+{
+  return ptr_4->m_colour; // { dg-error "'class t4' has no member named 'm_colour'; did you mean 'int t4::m_color'\\? \\(not accessible from this context\\)" }
+  /* { dg-begin-multiline-output "" }
+   return ptr_4->m_colour;
+                 ^~~~~~~~
+     { dg-end-multiline-output "" } */
+  /* { dg-begin-multiline-output "" }
+   int m_color;
+       ^~~~~~~
+     { dg-end-multiline-output "" } */
+}
+
+
+/* Misspelling of a private member, for which the accessor is also private.
+
+   We expect no fix-it hint; instead a message identifying where the
+   data member was declared.  */
+
+class t5
+{
+  int get_color (this const t5& x) { return x.m_color; }
+  int m_color; // { dg-message "declared private here" }
+};
+
+int test (t5 *ptr_5)
+{
+  return ptr_5->m_colour; // { dg-error "'class t5' has no member named 'm_colour'; did you mean 'int t5::m_color'\\? \\(not accessible from this context\\)" }
+  /* { dg-begin-multiline-output "" }
+   return ptr_5->m_colour;
+                 ^~~~~~~~
+     { dg-end-multiline-output "" } */
+  /* { dg-begin-multiline-output "" }
+   int m_color;
+       ^~~~~~~
+     { dg-end-multiline-output "" } */
+}
-- 
2.39.3