Re: [PATCH] c++: Suppress error when cv-qualified reference is introduced by typedef [PR101783]

[nick huang <nickhuang99@hotmail.com>]

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>>You may need to run contrib/gcc-git-customization.sh to get the git 
>>gcc-verify command.
I re-setup and can use git gcc-verify. Now I can see it rejects because I forgot to add a 
description of modified file. Now that it passes gcc-verify and I attach the changelog 
as attachment.

Thank you again for your patient explanation and help!



On 9/26/21 21:31, nick huang via Gcc-patches wrote:
> Hi Jason,
> 
> 1. Thank you very much for your detailed comments for my patch and I really appreciate it! Here is my revised patch:
> 
> The root cause of this bug is that it considers reference with
> cv-qualifiers as an error by generating value for variable "bad_quals".
> However, this is not correct for case of typedef. Here I quote spec:
> "Cv-qualified references are ill-formed except when the cv-qualifiers
> are introduced through the use of a typedef-name ([dcl.typedef],
> [temp.param]) or decltype-specifier ([dcl.type.decltype]),
> in which case the cv-qualifiers are ignored."
> 
> 2021-09-25  qingzhe huang  <nickhuang99@hotmail.com>
> 
> gcc/cp/
>        PR c++/101783
>        * tree.c (cp_build_qualified_type_real):

git gcc-verify still rejects this line with

ERR: missing description of a change: " * tree.c 
(cp_build_qualified_type_real):"

You may need to run contrib/gcc-git-customization.sh to get the git 
gcc-verify command.

> gcc/testsuite/
>        PR c++/101783
>        * g++.dg/parse/pr101783.C: New test.
> -------------- next part --------------

Please drop this line, it breaks git gcc-verify when I apply the patch 
with git am.  The patch should start immediately after the ChangeLog 
entries.

> diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
> index 8840932dba2..d5c8daeb340 100644
> --- a/gcc/cp/tree.c
> +++ b/gcc/cp/tree.c
> @@ -1356,11 +1356,18 @@ cp_build_qualified_type_real (tree type,
>     /* A reference or method type shall not be cv-qualified.
>        [dcl.ref], [dcl.fct].  This used to be an error, but as of DR 295
>        (in CD1) we always ignore extra cv-quals on functions.  */
> +
> +  /* Cv-qualified references are ill-formed except when the cv-qualifiers

In my previous reply I meant please add "[dcl.ref]/1" at the beginning 
of this comment.

> +     are introduced through the use of a typedef-name ([dcl.typedef],
> +     [temp.param]) or decltype-specifier ([dcl.type.decltype]),
> +     in which case the cv-qualifiers are ignored.
> +   */
>     if (type_quals & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE)
>         && (TYPE_REF_P (type)
>          || FUNC_OR_METHOD_TYPE_P (type)))
>       {
> -      if (TYPE_REF_P (type))
> +      if (TYPE_REF_P (type)
> +       && (!typedef_variant_p (type) || FUNC_OR_METHOD_TYPE_P (type)))
>        bad_quals |= type_quals & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE);
>         type_quals &= ~(TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE);
>       }
> diff --git a/gcc/testsuite/g++.dg/parse/pr101783.C b/gcc/testsuite/g++.dg/parse/pr101783.C
> new file mode 100644
> index 00000000000..4e0a435dd0b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/parse/pr101783.C
> @@ -0,0 +1,5 @@
> +template<class T> struct A{
> +        typedef T& Type;
> +};
> +template<class T> void f(const typename A<T>::Type){}
> +template <> void f<int>(const typename A<int>::Type){}
> 
> 
> 
> 2.
>> In Jonathan's earlier reply he asked how you tested the patch; this
>> message still doesn't say anything about that.
> I communicated with Mr. Jonathan in private email, worrying my naive question might pollute the public maillist. The following is major part of this communication and I attached original part in attachment.
> 
>>>> How has this patch been tested? Have you bootstrapped the compiler and
>>>> run the full testsuite?
> Here is how I am doing:
> a) build original 10.2.0 from scratch and make check to get both "testsuite/gcc/gcc.sum"
> and "testsuite/g++/g++.sum".
> b) apply my patch and build from scratch and make check to get both two files above.
> c) compare two run's *.sum files to see if there is any difference.
> 
>   (Later I realized there is tool  "contrib/compare_tests" is a good help of doing so.)
> 
> 3.
>> What is the legal status of your contributions?
> I thought small patch didn't require assignment. However, I just sent email to assign@gnu.org to request assignment.
> Alternatively, I am not sure if adding this "signoff" tag in submission will help?
> Signed-off-by: qingzhe huang <nickhuang99@hotmail.com>
> 
> 
> Thank you again!
> 
> 
>> On 8/28/21 07:54, nick huang via Gcc-patches wrote:
>>> Reference with cv-qualifiers should be ignored instead of causing an error
>>> because standard accepts cv-qualified references introduced by typedef which
>>> is ignored.
>>> Therefore, the fix prevents GCC from reporting error by not setting variable
>>> "bad_quals" in case the reference is introduced by typedef. Still the
>>> cv-qualifier is silently ignored.
>>> Here I quote spec (https://timsong-cpp.github.io/cppwp/dcl.ref#1):
>>> "Cv-qualified references are ill-formed except when the cv-qualifiers
>>> are introduced through the use of a typedef-name ([dcl.typedef],
>>> [temp.param]) or decltype-specifier ([dcl.type.decltype]),
>>> in which case the cv-qualifiers are ignored."
>>>
>>> PR c++/101783
>>>
>>> gcc/cp/ChangeLog:
>>>
>>> 2021-08-27  qingzhe huang  <nickhuang99@hotmail.com>
>>>
>>> * tree.c (cp_build_qualified_type_real):
>>
>> The git commit verifier rejects this commit message with
>>
>> Checking 1fa0fbcdd15adf936ab4fae584f841beb35da1bb: FAILED ERR: missing
>> description of a change:
>> " * tree.c (cp_build_qualified_type_real):"
>>
>> (your initial patch had a description here, you just need to copy it over)
>>
>> ERR: PR 101783 in subject but not in changelog:
>> "c++: Suppress error when cv-qualified reference is introduced by
>> typedef [PR101783]"
>>
>> (the PR number needs to have a Tab before it)
>>
>> In Jonathan's earlier reply he asked how you tested the patch; this
>> message still doesn't say anything about that.
>>
>> https://gcc.gnu.org/contribute.html#testing
>>
>> What is the legal status of your contributions?
>>
>> https://gcc.gnu.org/contribute.html#legal
>>
>> Existing code tries to handle this with the tf_ignore_bad_quals, but the
>> unnecessary use of typename gets past the code that tries to set the
>> flag.  But your approach is nice and straightforward, so let's go ahead
>> with it.
>>
>>> gcc/testsuite/ChangeLog:
>>>
>>> 2021-08-27  qingzhe huang  <nickhuang99@hotmail.com>
>>>
>>> * g++.dg/parse/pr101783.C: New test.
>>>
>>> diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
>>> index 8840932dba2..7aa4318a574 100644
>>> --- a/gcc/cp/tree.c
>>> +++ b/gcc/cp/tree.c
>>> @@ -1356,12 +1356,22 @@ cp_build_qualified_type_real (tree type,
>>>      /* A reference or method type shall not be cv-qualified.
>>>         [dcl.ref], [dcl.fct].  This used to be an error, but as of DR 295
>>>         (in CD1) we always ignore extra cv-quals on functions.  */
>>> +
>>> +  /* PR 101783
>>
>> Let's cite where this comes from in the standard ([dcl.ref]/1), and not
>> the PR number.
>>
>>> +     Cv-qualified references are ill-formed except when the cv-qualifiers
>>> +     are introduced through the use of a typedef-name ([dcl.typedef],
>>> +     [temp.param]) or decltype-specifier ([dcl.type.decltype]),
>>> +     in which case the cv-qualifiers are ignored.
>>> +   */
>>>      if (type_quals & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE)
>>>          && (TYPE_REF_P (type)
>>>     || FUNC_OR_METHOD_TYPE_P (type)))
>>>        {
>>> -      if (TYPE_REF_P (type))
>>> +      // do NOT set bad_quals when non-method reference is introduced by typedef.
>>> +      if (TYPE_REF_P (type)
>>> +  && (!typedef_variant_p (type) || FUNC_OR_METHOD_TYPE_P (type)))
>>>    bad_quals |= type_quals & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE);
>>> +      // non-method reference introduced by typedef is also dropped silently
>>
>> These two // comments seem redundant with the quote from the standard
>> above, let's drop them.
>>
>>>          type_quals &= ~(TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE);
>>>        }
>>>   
>>> diff --git a/gcc/testsuite/g++.dg/parse/pr101783.C b/gcc/testsuite/g++.dg/parse/pr101783.C
>>> new file mode 100644
>>> index 00000000000..4e0a435dd0b
>>> --- /dev/null
>>> +++ b/gcc/testsuite/g++.dg/parse/pr101783.C
>>> @@ -0,0 +1,5 @@
>>> +template<class T> struct A{
>>> +        typedef T& Type;
>>> +};
>>> +template<class T> void f(const typename A<T>::Type){}
>>> +template <> void f<int>(const typename A<int>::Type){}
>>>
>>>

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The root cause of this bug is that it considers reference with
cv-qualifiers as an error by generating value for variable "bad_quals".
However, this is not correct for case of typedef. Here I quote spec
[dcl.ref]/1 :
"Cv-qualified references are ill-formed except when the cv-qualifiers
are introduced through the use of a typedef-name ([dcl.typedef],
[temp.param]) or decltype-specifier ([dcl.type.decltype]),
in which case the cv-qualifiers are ignored."

2021-09-30  qingzhe huang  <nickhuang99@hotmail.com>

gcc/cp/ChangeLog:
    PR c++/101783
    * tree.c (cp_build_qualified_type_real): Excluding typedef from error

gcc/testsuite/ChangeLog:
    PR c++/101783
    * g++.dg/parse/pr101783.C: New test.

diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index 8840932dba2..cdc27facf02 100644
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -1356,11 +1356,18 @@ cp_build_qualified_type_real (tree type,
   /* A reference or method type shall not be cv-qualified.
      [dcl.ref], [dcl.fct].  This used to be an error, but as of DR 295
      (in CD1) we always ignore extra cv-quals on functions.  */
+
+  /* [dcl.ref/1] Cv-qualified references are ill-formed except when
+     the cv-qualifiers are introduced through the use of a typedef-name
+     ([dcl.typedef], [temp.param]) or decltype-specifier
+     ([dcl.type.decltype]),in which case the cv-qualifiers are ignored.
+  */
   if (type_quals & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE)
       && (TYPE_REF_P (type)
 	  || FUNC_OR_METHOD_TYPE_P (type)))
     {
-      if (TYPE_REF_P (type))
+      if (TYPE_REF_P (type)
+	  && (!typedef_variant_p (type) || FUNC_OR_METHOD_TYPE_P (type)))
 	bad_quals |= type_quals & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE);
       type_quals &= ~(TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE);
     }
diff --git a/gcc/testsuite/g++.dg/parse/pr101783.C b/gcc/testsuite/g++.dg/parse/pr101783.C
new file mode 100644
index 00000000000..4e0a435dd0b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/pr101783.C
@@ -0,0 +1,5 @@
+template<class T> struct A{
+        typedef T& Type;
+};
+template<class T> void f(const typename A<T>::Type){}
+template <> void f<int>(const typename A<int>::Type){}