[PATCH] wwwdocs: Add ADL to C++ non-bugs

[PATCH] wwwdocs: Add ADL to C++ non-bugs

[Jonathan Wakely]

We have a long history of INVALID bugs about std functions being
available in the global namespace (PRs 27846, 67566, 82619, 99865,
110602, 111553, probably others). Let's document it.

Also de-prioritize the C++98-only bugs, which are unlikely to affect
anybody nowadays.

OK for wwwdocs?

-- >8 --

Add ADL to C++ non-bugs

Also move the item about C++98 'export' to the end, and update the item
about <: digraphs that only applies to C++98.

---
 htdocs/bugs/index.html | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/htdocs/bugs/index.html b/htdocs/bugs/index.html
index 813b78c0..41edc561 100644
--- a/htdocs/bugs/index.html
+++ b/htdocs/bugs/index.html
@@ -539,15 +539,15 @@ for details.
 <h2 id="nonbugs_cxx">C++</h2>
 
 <dl>
-<dt><code>export</code></dt>
-<dd><p>Most C++ compilers (G++ included) never implemented C++98
-<code>export</code>, which was removed in C++11, and the keyword reused in
-C++20 by the Modules feature. The C++98 feature was intended to support
-separate compilation of template declarations and
-definitions. Without <code>export</code>, a template definition must be in
-scope to be used. The obvious workaround is simply to place all definitions in
-the header itself. Alternatively, the compilation unit containing template
-definitions may be included from the header.</p></dd>
+<dt>Functions can be called without qualifying them with their namespace.</dt>
+<dd>
+Argument Dependent Lookup (ADL) means that functions can be found in namespaces
+associated with their arguments. This means that <code>move(arg)</code> can
+call <code>std::move</code> if <code>arg</code> is a type defined in namespace
+<code>std</code>, such as <code>std::string</code> or <code>std::vector</code>.
+If <code>std::move</code> is not the function you intended to call, use a
+qualified name such as <code>::move(arg)</code> or <code>foo::move(arg)</code>.
+</dd>
 
 <dt>Nested classes can access private members and types of the containing
 class.</dt>
@@ -597,9 +597,9 @@ handler and catch it in the main thread.</p></dd>
 <dd><p>If you have a class in the global namespace, say named <code>X</code>,
 and want to give it as a template argument to some other class, say
 <code>std::vector</code>, then <code>std::vector&lt;::X&gt;</code>
-fails with a parser error.</p>
+fails with a parser error in C++98/C++03 mode.</p>
 
-<p>The reason is that the standard mandates that the sequence
+<p>The reason is that the C++98 standard mandates that the sequence
 <code>&lt;:</code> is treated as if it were the token <code>[</code>.
 (There are several such combinations of characters - they are called
 <em>digraphs</em>.) Depending on the version, the compiler then reports
@@ -608,7 +608,19 @@ a parse error before the character <code>:</code> (the colon before
 
 <p>The simplest way to avoid this is to write <code>std::vector&lt;
 ::X&gt;</code>, i.e. place a space between the opening angle bracket
-and the scope operator.</p></dd>
+and the scope operator, or compile using C++11 or later. Defect report 1104
+changed the parser rules so that <code>&lt;::</code> works as expected.
+</p></dd>
+
+<dt><code>export</code></dt>
+<dd><p>Most C++ compilers (G++ included) never implemented C++98
+<code>export</code>, which was removed in C++11, and the keyword reused in
+C++20 by the Modules feature. The C++98 feature was intended to support
+separate compilation of template declarations and
+definitions. Without <code>export</code>, a template definition must be in
+scope to be used. The obvious workaround is simply to place all definitions in
+the header itself. Alternatively, the compilation unit containing template
+definitions may be included from the header.</p></dd>
 </dl>
 
 <h3 id="upgrading">Common problems when upgrading the compiler</h3>
-- 
2.41.0

Re: [PATCH] wwwdocs: Add ADL to C++ non-bugs

[Jason Merrill]

On 10/3/23 10:45, Jonathan Wakely wrote:
> We have a long history of INVALID bugs about std functions being
> available in the global namespace (PRs 27846, 67566, 82619, 99865,
> 110602, 111553, probably others). Let's document it.
> 
> Also de-prioritize the C++98-only bugs, which are unlikely to affect
> anybody nowadays.
> 
> OK for wwwdocs?

OK, thanks.

Jason

Re: [PATCH] wwwdocs: Add ADL to C++ non-bugs

[Jonathan Wakely]

[-- Attachment #1: Type: text/plain, Size: 606 bytes --]

On Wed, 4 Oct 2023 at 20:17, Jason Merrill <jason@redhat.com> wrote:
>
> On 10/3/23 10:45, Jonathan Wakely wrote:
> > We have a long history of INVALID bugs about std functions being
> > available in the global namespace (PRs 27846, 67566, 82619, 99865,
> > 110602, 111553, probably others). Let's document it.
> >
> > Also de-prioritize the C++98-only bugs, which are unlikely to affect
> > anybody nowadays.
> >
> > OK for wwwdocs?
>
> OK, thanks.
>
> Jason


After pushing it I realised the formatting looks bad compared to the
other items in the list, so I've pushed the attached follow-up as
obvious.

[-- Attachment #2: patch.txt --]
[-- Type: text/plain, Size: 1026 bytes --]

commit 1b1a0cf29826ce9287a203cde00fd1512918fc17
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Oct 5 10:09:54 2023 +0100

    Add <p> to new item in C++ non-bugs list

diff --git a/htdocs/bugs/index.html b/htdocs/bugs/index.html
index 41edc561..da3d4c0d 100644
--- a/htdocs/bugs/index.html
+++ b/htdocs/bugs/index.html
@@ -541,12 +541,14 @@ for details.
 <dl>
 <dt>Functions can be called without qualifying them with their namespace.</dt>
 <dd>
+<p>
 Argument Dependent Lookup (ADL) means that functions can be found in namespaces
 associated with their arguments. This means that <code>move(arg)</code> can
 call <code>std::move</code> if <code>arg</code> is a type defined in namespace
 <code>std</code>, such as <code>std::string</code> or <code>std::vector</code>.
 If <code>std::move</code> is not the function you intended to call, use a
 qualified name such as <code>::move(arg)</code> or <code>foo::move(arg)</code>.
+</p>
 </dd>
 
 <dt>Nested classes can access private members and types of the containing