[latex3-commits] [git/LaTeX3-latex3-latex3] master: fix #808 (3db75c3f8)

[Bruno Le Floch]

Repository : https://github.com/latex3/latex3
On branch  : master
Link       : https://github.com/latex3/latex3/commit/3db75c3f835a5e78617e0f365b3587a6e4c7bfab

>---------------------------------------------------------------

commit 3db75c3f835a5e78617e0f365b3587a6e4c7bfab
Author: Jonathan Spratte <jspratte at yahoo.de>
Date:   Sat Sep 19 22:14:44 2020 +0200

    fix #808


>---------------------------------------------------------------

3db75c3f835a5e78617e0f365b3587a6e4c7bfab
 l3kernel/l3tl.dtx | 57 +++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 36 insertions(+), 21 deletions(-)

diff --git a/l3kernel/l3tl.dtx b/l3kernel/l3tl.dtx
index f8e2e8a40..5f97365c8 100644
--- a/l3kernel/l3tl.dtx
+++ b/l3kernel/l3tl.dtx
@@ -3042,6 +3042,8 @@
 % \begin{macro}[pTF]{\tl_if_head_eq_charcode:nN}
 % \begin{macro}[pTF]{\tl_if_head_eq_charcode:fN}
 % \begin{macro}[pTF]{\tl_if_head_eq_catcode:nN}
+% \begin{macro}[EXP]{\@@_head_exp_not:w}
+% \begin{macro}[EXP]{\@@_if_head_eq_empty_arg:w}
 %   Accessing the first token of a token list is tricky in three cases:
 %   when it has category code $1$ (begin-group token), when it is an
 %   explicit space, with category code $10$ and character code $32$, or
@@ -3061,21 +3063,17 @@
 %   cases, the first token is a character, and since we only care about
 %   its character code, we can use \cs{str_head:n} to access it (this
 %   works even if it is a space character).  An empty argument
-%   results in \cs{tl_head:w} leaving two tokens: |?| which is taken in
-%   the \cs{if_charcode:w} test, and \cs{use_none:nn}, which ensures
-%   that \cs{prg_return_false:} is returned regardless of whether the
-%   charcode test was \texttt{true} or \texttt{false}.
+%   results in \cs{tl_head:w} leaving two token: |^| and
+%   \cs{@@_if_head_eq_empty_arg:w} which will result in the \cs{if_charcode:w}
+%   test being false and remove \cs{exp_not:N} and |#2|.
 %    \begin{macrocode}
 \prg_new_conditional:Npnn \tl_if_head_eq_charcode:nN #1#2 { p , T , F , TF }
   {
     \if_charcode:w
-        \exp_not:N #2
         \tl_if_head_is_N_type:nTF { #1 ? }
-          {
-            \exp_after:wN \exp_not:N
-            \@@_tl_head:w #1 { ? \use_none:nn } \s_@@_stop
-          }
+          { \@@_head_exp_not:w #1 { ^ \@@_if_head_eq_empty_arg:w } \s_@@_stop }
           { \str_head:n {#1} }
+        \exp_not:N #2
       \prg_return_true:
     \else:
       \prg_return_false:
@@ -3089,24 +3087,20 @@
 %   first token is a begin-group token or an explicit space token, and
 %   produce the relevant token, either \cs{c_group_begin_token} or
 %   \cs{c_space_token}.  Again, for an empty argument, a hack is used,
-%   removing \cs{prg_return_true:} and \cs{else:} with \cs{use_none:nn}
-%   in case the catcode test with the (arbitrarily chosen) |?| is
-%   \texttt{true}.
+%   removing the token given by the user and leaving two tokens in the input
+%   stream which will make the \cs{if_catcode:w} test return \texttt{false}.
 %    \begin{macrocode}
 \prg_new_conditional:Npnn \tl_if_head_eq_catcode:nN #1 #2 { p , T , F , TF }
   {
     \if_catcode:w
-        \exp_not:N #2
         \tl_if_head_is_N_type:nTF { #1 ? }
-          {
-            \exp_after:wN \exp_not:N
-            \@@_tl_head:w #1 { ? \use_none:nn } \s_@@_stop
-          }
+          { \@@_head_exp_not:w #1 { ^ \@@_if_head_eq_empty_arg:w } \s_@@_stop }
           {
             \tl_if_head_is_group:nTF {#1}
-              { \c_group_begin_token }
-              { \c_space_token }
+              \c_group_begin_token
+              \c_space_token
           }
+        \exp_not:N #2
       \prg_return_true:
     \else:
       \prg_return_false:
@@ -3129,8 +3123,8 @@
 \prg_new_conditional:Npnn \tl_if_head_eq_meaning:nN #1#2 { p , T , F , TF }
   {
     \tl_if_head_is_N_type:nTF { #1 ? }
-      { \@@_if_head_eq_meaning_normal:nN }
-      { \@@_if_head_eq_meaning_special:nN }
+      \@@_if_head_eq_meaning_normal:nN
+      \@@_if_head_eq_meaning_special:nN
     {#1} #2
   }
 \cs_new:Npn \@@_if_head_eq_meaning_normal:nN #1 #2
@@ -3162,6 +3156,27 @@
     }
   }
 %    \end{macrocode}
+%
+%   Both \cs{tl_if_head_eq_charcode:nN} and \cs{tl_if_head_eq_catcode:nN} will
+%   need to get the first token of their argument and apply \cs{exp_not:N} to
+%   it. \cs{@@_head_exp_not:w} does exactly that.
+%    \begin{macrocode}
+\cs_new:Npn \@@_head_exp_not:w #1 #2 \s_@@_stop
+  { \exp_not:N #1 }
+%    \end{macrocode}
+%
+%   If the argument of \cs{tl_if_head_eq_charcode:nN} and
+%   \cs{tl_if_head_eq_catcode:nN} was empty \cs{@@_if_head_eq_empty_arg:w} will
+%   be left in the input stream. This macro has to remove \cs{exp_not:N} and
+%   the following token from the input stream to make sure no unbalanced
+%   if-construct is created and leave tokens there which make the two tests
+%   return \texttt{false}.
+%    \begin{macrocode}
+\cs_new:Npn \@@_if_head_eq_empty_arg:w \exp_not:N #1
+  { ? }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
 % \end{macro}
 % \end{macro}
 % \end{macro}