[PATCH] libstdc++: Document that _GLIBCXX_CONCEPT_CHECKS might be removed in future

[PATCH] libstdc++: Document that _GLIBCXX_CONCEPT_CHECKS might be removed in future

[Jonathan Wakely]

Any objection to this update to make the docs reflect reality?

-- >8 --

The macro-based concept checks are unmaintained and do not support C++11
or later, so reject valid code. If nobody plans to update them we should
consider removing them. Alternatively, we could ignore the macro for
C++11 and later, so they have no effect and don't reject valid code.

libstdc++-v3/ChangeLog:

	* doc/xml/manual/debug.xml: Document that concept checking might
	be removed in future.
	* doc/xml/manual/extensions.xml: Likewise.
---
 libstdc++-v3/doc/xml/manual/debug.xml      |  2 ++
 libstdc++-v3/doc/xml/manual/extensions.xml | 18 ++++++++++++------
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/libstdc++-v3/doc/xml/manual/debug.xml b/libstdc++-v3/doc/xml/manual/debug.xml
index 42d4d32aa29..7f6d0876fc6 100644
--- a/libstdc++-v3/doc/xml/manual/debug.xml
+++ b/libstdc++-v3/doc/xml/manual/debug.xml
@@ -351,6 +351,8 @@
 
   <para> The <link linkend="manual.ext.compile_checks">Compile-Time
   Checks</link> extension has compile-time checks for many algorithms.
+  These checks were designed for C++98 and have not been updated to work
+  with C++11 and later standards. They might be removed at a future date.
   </para>
 </section>
 
diff --git a/libstdc++-v3/doc/xml/manual/extensions.xml b/libstdc++-v3/doc/xml/manual/extensions.xml
index d4fe2f509d4..490a50cc331 100644
--- a/libstdc++-v3/doc/xml/manual/extensions.xml
+++ b/libstdc++-v3/doc/xml/manual/extensions.xml
@@ -77,8 +77,7 @@ extensions, be aware of two things:
       object file.  The checks are also cleaner and easier to read and
       understand.
    </para>
-   <para>They are off by default for all versions of GCC from 3.0 to 3.4 (the
-      latest release at the time of writing).
+   <para>They are off by default for all GCC 3.0 and all later versions.
       They can be enabled at configure time with
       <link linkend="manual.intro.setup.configure"><literal>--enable-concept-checks</literal></link>.
       You can enable them on a per-translation-unit basis with
@@ -89,10 +88,17 @@ extensions, be aware of two things:
    </para>
 
    <para>Please note that the concept checks only validate the requirements
-   of the old C++03 standard. C++11 was expected to have first-class
-   support for template parameter constraints based on concepts in the core
-   language. This would have obviated the need for the library-simulated concept
-   checking described above, but was not part of C++11.
+   of the old C++03 standard and reject some valid code that meets the relaxed
+   requirements of C++11 and later standards.
+   C++11 was expected to have first-class support for template parameter
+   constraints based on concepts in the core language.
+   This would have obviated the need for the library-simulated concept checking
+   described above, but was not part of C++11.
+   C++20 adds a different model of concepts, which is now used to constrain
+   some new parts of the C++20 library, e.g. the
+   <filename>&lt;ranges&gt;</filename> header and the new overloads in the
+   <filename>&lt;algorithm&gt;</filename> header for working with ranges.
+   The old library-simulated concept checks might be removed at a future date.
    </para>
 
 </chapter>
-- 
2.43.2

Re: [PATCH] libstdc++: Document that _GLIBCXX_CONCEPT_CHECKS might be removed in future

[Jonathan Wakely]

On Thu, 7 Mar 2024 at 12:07, Jonathan Wakely wrote:
>
> Any objection to this update to make the docs reflect reality?

Pushed to trunk now.


>
> -- >8 --
>
> The macro-based concept checks are unmaintained and do not support C++11
> or later, so reject valid code. If nobody plans to update them we should
> consider removing them. Alternatively, we could ignore the macro for
> C++11 and later, so they have no effect and don't reject valid code.
>
> libstdc++-v3/ChangeLog:
>
>         * doc/xml/manual/debug.xml: Document that concept checking might
>         be removed in future.
>         * doc/xml/manual/extensions.xml: Likewise.
> ---
>  libstdc++-v3/doc/xml/manual/debug.xml      |  2 ++
>  libstdc++-v3/doc/xml/manual/extensions.xml | 18 ++++++++++++------
>  2 files changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/libstdc++-v3/doc/xml/manual/debug.xml b/libstdc++-v3/doc/xml/manual/debug.xml
> index 42d4d32aa29..7f6d0876fc6 100644
> --- a/libstdc++-v3/doc/xml/manual/debug.xml
> +++ b/libstdc++-v3/doc/xml/manual/debug.xml
> @@ -351,6 +351,8 @@
>
>    <para> The <link linkend="manual.ext.compile_checks">Compile-Time
>    Checks</link> extension has compile-time checks for many algorithms.
> +  These checks were designed for C++98 and have not been updated to work
> +  with C++11 and later standards. They might be removed at a future date.
>    </para>
>  </section>
>
> diff --git a/libstdc++-v3/doc/xml/manual/extensions.xml b/libstdc++-v3/doc/xml/manual/extensions.xml
> index d4fe2f509d4..490a50cc331 100644
> --- a/libstdc++-v3/doc/xml/manual/extensions.xml
> +++ b/libstdc++-v3/doc/xml/manual/extensions.xml
> @@ -77,8 +77,7 @@ extensions, be aware of two things:
>        object file.  The checks are also cleaner and easier to read and
>        understand.
>     </para>
> -   <para>They are off by default for all versions of GCC from 3.0 to 3.4 (the
> -      latest release at the time of writing).
> +   <para>They are off by default for all GCC 3.0 and all later versions.
>        They can be enabled at configure time with
>        <link linkend="manual.intro.setup.configure"><literal>--enable-concept-checks</literal></link>.
>        You can enable them on a per-translation-unit basis with
> @@ -89,10 +88,17 @@ extensions, be aware of two things:
>     </para>
>
>     <para>Please note that the concept checks only validate the requirements
> -   of the old C++03 standard. C++11 was expected to have first-class
> -   support for template parameter constraints based on concepts in the core
> -   language. This would have obviated the need for the library-simulated concept
> -   checking described above, but was not part of C++11.
> +   of the old C++03 standard and reject some valid code that meets the relaxed
> +   requirements of C++11 and later standards.
> +   C++11 was expected to have first-class support for template parameter
> +   constraints based on concepts in the core language.
> +   This would have obviated the need for the library-simulated concept checking
> +   described above, but was not part of C++11.
> +   C++20 adds a different model of concepts, which is now used to constrain
> +   some new parts of the C++20 library, e.g. the
> +   <filename>&lt;ranges&gt;</filename> header and the new overloads in the
> +   <filename>&lt;algorithm&gt;</filename> header for working with ranges.
> +   The old library-simulated concept checks might be removed at a future date.
>     </para>
>
>  </chapter>
> --
> 2.43.2
>