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

[nick huang <nickhuang99@hotmail.com>]

[-- 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.