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

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

[nick huang]

[-- Attachment #1: Type: text/plain, Size: 7597 bytes --]

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):

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

[-- Attachment #2: how-to-test.txt --]
[-- Type: text/plain, Size: 1463 bytes --]

> >>>How has this ptch 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".
> This is my configure params:
>
> configure --prefix=/home/nick/Downloads/gcc-10.2.0-test/gcc_install/gcc-10.2.0_install

> --enable-bootstrap --enable-shared --enable-threads=posix

These are enabled by default.

>  --enable-checking=release

You don't want this when testing changes on trunk, it disables important checks.


> --enable-__cxa_atexit --disable-libunwind-exceptions --enable-linker-build-id

All enabled by default.


>--enable-languages=c,c++,lto --disable-vtable-verify --with-default-libstdcxx-abi=new --enable-libstdcxx-debug --without-included-gettext --enable-plugin --disable-initfini-array --disable-libgcj --enable-plugin --disable-multilib --with-tune=generic --build=x86_64-unknown-linux-gnu --target=x86_64-unknown-linux-gnu --host=x86_64-unknown-linux-gnu --with-pkgversion=nick-nick-HP-Laptop
>
> 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.
>
> If above procedure is correct,

Your configure command is overcomplicated, but apart from the
--enable-checking option it is harmless.


>I will re-do and re-submit the patch email with corrected PR number.

Yes, please do.

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

[Jason Merrill]

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){}
>>>
>>>

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

[nick huang]

[-- Attachment #1: Type: text/plain, Size: 8739 bytes --]

>>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){}
>>>
>>>

[-- Attachment #2: pr101783.txt --]
[-- Type: text/plain, Size: 2158 bytes --]

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){}

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

[Jason Merrill]

On 9/30/21 14:24, nick huang wrote:
>>> 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!

You're welcome, thanks for your patience as well!  Unfortunately, git 
gcc-verify still fails with this version:

> ERR: line should start with a tab: "    PR c++/101783"
> ERR: line should start with a tab: "    * tree.c (cp_build_qualified_type_real): Excluding typedef from error"
> ERR: line should start with a tab: "    PR c++/101783"
> ERR: line should start with a tab: "    * g++.dg/parse/pr101783.C: New test."

It might work better to attach the output of git format-patch.

Also, your commit subject line is too long, at 83 characters: It must be 
under 75 characters, and preferably closer to 50.  I might shorten it to

c++: cv-qualified ref introduced by typedef [PR101783]

>     * tree.c (cp_build_qualified_type_real): Excluding typedef from error

A change description in the ChangeLog should use present tense 
("Exclude"), have a period at the end, and line wrap at 75 characters 
like the rest of the commit message.  So,

	* tree.c (cp_build_qualified_type_real): Exclude typedef from
	error.

> +     ([dcl.type.decltype]),in which case the cv-qualifiers are ignored.        
> +  */                                                                           

We usually don't put */ on its own line.

Jason

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

[Nick Huang]

[-- Attachment #1: Type: text/plain, Size: 3203 bytes --]

> gcc-verify still fails with this version:
>
> > ERR: line should start with a tab: "    PR c++/101783"
> > ERR: line should start with a tab: "    * tree.c (cp_build_qualified_type_real): Excluding typedef from error"
> > ERR: line should start with a tab: "    PR c++/101783"
> > ERR: line should start with a tab: "    * g++.dg/parse/pr101783.C: New test."

> It might work better to attach the output of git format-patch.
Sorry for my clumsy copy/paste from git commit message. I now attach
git format-patch output
file as attachment. Also maybe for a little convenience of your work,
I also attach the original
commit message file when I do git commit -F.

> Also, your commit subject line is too long, at 83 characters: It must be
> under 75 characters, and preferably closer to 50.  I might shorten it to

Please go ahead. I will pay attention to this next time. Thank you!

> A change description in the ChangeLog should use present tense
> ("Exclude"), have a period at the end, and line wrap at 75 characters
> like the rest of the commit message.  So,
>
>         * tree.c (cp_build_qualified_type_real): Exclude typedef from
>         error.
>

Modified as suggested.

> > +     ([dcl.type.decltype]),in which case the cv-qualifiers are ignored.
> > +  */
>
> We usually don't put */ on its own line.

Adjusted.

Once again I thank you for your patience and really appreciate it.

On Fri, Oct 1, 2021 at 9:29 AM Jason Merrill via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On 9/30/21 14:24, nick huang wrote:
> >>> 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!
>
> You're welcome, thanks for your patience as well!  Unfortunately, git
> gcc-verify still fails with this version:
>
> > ERR: line should start with a tab: "    PR c++/101783"
> > ERR: line should start with a tab: "    * tree.c (cp_build_qualified_type_real): Excluding typedef from error"
> > ERR: line should start with a tab: "    PR c++/101783"
> > ERR: line should start with a tab: "    * g++.dg/parse/pr101783.C: New test."
>
> It might work better to attach the output of git format-patch.
>
> Also, your commit subject line is too long, at 83 characters: It must be
> under 75 characters, and preferably closer to 50.  I might shorten it to
>
> c++: cv-qualified ref introduced by typedef [PR101783]
>
> >     * tree.c (cp_build_qualified_type_real): Excluding typedef from error
>
> A change description in the ChangeLog should use present tense
> ("Exclude"), have a period at the end, and line wrap at 75 characters
> like the rest of the commit message.  So,
>
>         * tree.c (cp_build_qualified_type_real): Exclude typedef from
>         error.
>
> > +     ([dcl.type.decltype]),in which case the cv-qualifiers are ignored.
> > +  */
>
> We usually don't put */ on its own line.
>
> Jason
>


-- 
nick huang/qingzhe huang
http://www.staroceans.com
http://www.staroceans.com/english.htm

[-- Attachment #2: commit-comment-10-01.txt --]
[-- Type: text/plain, Size: 697 bytes --]

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): Exclude typedef from 
	error.

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


[-- Attachment #3: 0001-The-root-cause-of-this-bug-is-that-it-considers-refe.patch --]
[-- Type: text/x-patch, Size: 2551 bytes --]

From e592a475030d99647de736d294cb3c6a7588af49 Mon Sep 17 00:00:00 2001
From: qingzhe huang <nickhuang99@hotmail.com>
Date: Fri, 1 Oct 2021 10:46:35 -0400
Subject: [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
 [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): Exclude typedef from
	error.

gcc/testsuite/ChangeLog:
	PR c++/101783
	* g++.dg/parse/pr101783.C: New test.
---
 gcc/cp/tree.c                         | 9 ++++++++-
 gcc/testsuite/g++.dg/parse/pr101783.C | 5 +++++
 2 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/parse/pr101783.C

diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index 8840932dba2..6a6f8a642cb 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){}
-- 
2.17.1

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

[Jason Merrill]

On 10/1/21 11:10, Nick Huang wrote:
>> gcc-verify still fails with this version:
>>
>>> ERR: line should start with a tab: "    PR c++/101783"
>>> ERR: line should start with a tab: "    * tree.c (cp_build_qualified_type_real): Excluding typedef from error"
>>> ERR: line should start with a tab: "    PR c++/101783"
>>> ERR: line should start with a tab: "    * g++.dg/parse/pr101783.C: New test."
> 
>> It might work better to attach the output of git format-patch.
> Sorry for my clumsy copy/paste from git commit message. I now attach
> git format-patch output
> file as attachment. Also maybe for a little convenience of your work,
> I also attach the original
> commit message file when I do git commit -F.

Thanks, but that isn't necessary; it should be the same in the 
format-patch output, except...

> From e592a475030d99647de736d294cb3c6a7588af49 Mon Sep 17 00:00:00 2001
> From: qingzhe huang <nickhuang99@hotmail.com>
> Date: Fri, 1 Oct 2021 10:46:35 -0400
> Subject: [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
>  [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."

...the subject line for the commit should be the first line of the 
commit message, followed by a blank line, followed by the description of 
the patch; without the subject line, git format-patch thought your whole 
description was the subject of the patch.

I've corrected this and pushed the patch, thanks!

Jason

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

[Nick Huang]

> ...the subject line for the commit should be the first line of the
> commit message, followed by a blank line, followed by the description of
> the patch; without the subject line, git format-patch thought your whole
> description was the subject of the patch.

oh,  I didn't realize this without your mentioning it. I read this guide
(https://gcc.gnu.org/codingconventions.html#ChangeLogs) many times
and still don't get this. I guess it was written long long ago.

> I've corrected this and pushed the patch, thanks!
I do thank you and without your help I might  never accomplish this task.
Once again appreciate your patient help!

On Fri, Oct 1, 2021 at 11:46 AM Jason Merrill <jason@redhat.com> wrote:
>
> On 10/1/21 11:10, Nick Huang wrote:
> >> gcc-verify still fails with this version:
> >>
> >>> ERR: line should start with a tab: "    PR c++/101783"
> >>> ERR: line should start with a tab: "    * tree.c (cp_build_qualified_type_real): Excluding typedef from error"
> >>> ERR: line should start with a tab: "    PR c++/101783"
> >>> ERR: line should start with a tab: "    * g++.dg/parse/pr101783.C: New test."
> >
> >> It might work better to attach the output of git format-patch.
> > Sorry for my clumsy copy/paste from git commit message. I now attach
> > git format-patch output
> > file as attachment. Also maybe for a little convenience of your work,
> > I also attach the original
> > commit message file when I do git commit -F.
>
> Thanks, but that isn't necessary; it should be the same in the
> format-patch output, except...
>
> > From e592a475030d99647de736d294cb3c6a7588af49 Mon Sep 17 00:00:00 2001
> > From: qingzhe huang <nickhuang99@hotmail.com>
> > Date: Fri, 1 Oct 2021 10:46:35 -0400
> > Subject: [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
> >  [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."
>
> ...the subject line for the commit should be the first line of the
> commit message, followed by a blank line, followed by the description of
> the patch; without the subject line, git format-patch thought your whole
> description was the subject of the patch.
>
> I've corrected this and pushed the patch, thanks!
>
> Jason
>


-- 
nick huang/qingzhe huang
http://www.staroceans.com
http://www.staroceans.com/english.htm

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

[Jason Merrill]

On 10/1/21 15:52, Nick Huang wrote:
>> ...the subject line for the commit should be the first line of the
>> commit message, followed by a blank line, followed by the description of
>> the patch; without the subject line, git format-patch thought your whole
>> description was the subject of the patch.
> 
> oh,  I didn't realize this without your mentioning it. I read this guide
> (https://gcc.gnu.org/codingconventions.html#ChangeLogs) many times
> and still don't get this. I guess it was written long long ago.

FYI that's a git thing, not a ChangeLog thing.  From the git 
format-patch manual:

>        By default, the subject of a single patch is "[PATCH] " followed by the
>        concatenation of lines from the commit message up to the first blank
>        line (see the DISCUSSION section of git-commit(1)).

And from git-commit(1):

>        Though not required, it’s a good idea to begin the commit message with
>        a single short (less than 50 character) line summarizing the change,
>        followed by a blank line and then a more thorough description. The text
>        up to the first blank line in a commit message is treated as the commit
>        title, and that title is used throughout Git. For example, git-format-
>        patch(1) turns a commit into email, and it uses the title on the
>        Subject line and the rest of the commit in the body.
But yes, it would be good to give more of this instruction in the gcc 
contribute.html.

Jason

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

[Jason Merrill]

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){}
> 
> 
> 

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

[nick huang]

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):

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
+     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
       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){}