Improve handling of \exp_not:n in \text_expand:n (fixes #875)

latex3 · Apr 24, 2021 · 30d827a · 30d827a
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diff --git a/l3kernel/CHANGELOG.md b/l3kernel/CHANGELOG.md
@@ -15,7 +15,8 @@ this project uses date-based 'snapshot' version identifiers.
 ### Changed
 - `\__kernel_file_name_sanitize:n` now uses a faster `\csname`-based
   approach to expand the file name.
-- `\pdf_version_gset:n` for `dvips`.  
+- `\pdf_version_gset:n` for `dvips`.
+- Improve handling of `\exp_not:n` in `\text_expand:n` (issue #875)
 
 ### Fixed
 - Evalutate integer constants only once (issue#861)

diff --git a/l3kernel/l3text.dtx b/l3kernel/l3text.dtx
@@ -637,6 +637,7 @@
 % \begin{macro}[EXP]{\@@_expand_replace:N}
 % \begin{macro}[EXP]{\@@_expand_replace:n}
 % \begin{macro}[EXP]{\@@_expand_cs_expand:N}
+% \begin{macro}[EXP]{\@@_expand_noexpand:w}
 % \begin{macro}[EXP]{\@@_expand_noexpand:nn}
 %   After precautions against |&| tokens, start a simple loop: that of
 %   course means that \enquote{text} cannot contain the two recursion
@@ -996,14 +997,19 @@
 %   Finally, expand any macros which can be: this then loops back around to
 %   deal with what they produce. The only issue is if the token is
 %   \cs{exp_not:n}, as that must apply to the following balanced text.
-%   There might be an \cs{exp_after:wN} there, so we check for it.
+%   Expand everything that follows such an \cs{exp_not:n} (in principle
+%   we should actually expand tokens and discard any spaces or \cs{scan_stop:},
+%   but this is messy to ensure safely).
 %    \begin{macrocode}
 \cs_new:Npn \@@_expand_cs_expand:N #1
   {
     \@@_if_expandable:NTF #1
       {
         \token_if_eq_meaning:NNTF #1 \exp_not:n
-          { \@@_expand_noexpand:w }
+          {
+            \exp_after:wN \@@_expand_noexpand:w
+            \exp:w \exp_end_continue_f:w
+          }
           { \exp_after:wN \@@_expand_loop:w #1 }
       }
       {
@@ -1015,7 +1021,8 @@
   { \@@_expand_noexpand:nn {#1} }
 \cs_new:Npn \@@_expand_noexpand:nn #1#2
   {
-    #1 \@@_expand_store:n #1 {#2}
+    \exp_after:wN \@@_expand_store:n \exp_after:wN
+      { \__kernel_exp_not:w #1 {#2} }
     \@@_expand_loop:w
   }
 %    \end{macrocode}
@@ -1050,6 +1057,7 @@
 % \end{macro}
 % \end{macro}
 % \end{macro}
+% \end{macro}
 %
 % \begin{macro}
 %   {

diff --git a/l3kernel/testfiles/m3text001.lvt b/l3kernel/testfiles/m3text001.lvt
@@ -43,6 +43,7 @@
     \text_expand:n { Some~text~$y~=~\sin \theta$ }
     \NEWLINE
     \text_expand:n { Opps~not~close~token~in~$y~=~\sin \theta }
+    % $ % make some code-highlighters happy
   }
 
 \TESTEXP { Letter-like~commands }
@@ -82,4 +83,10 @@
       { \text_expand:n { \tl_map_tokens:nn { { \NoCaseChange { c } } } { tokens } } }
   }
 
+\TEST { Expansion~noexpand }
+  {
+    \tl_show:x { \text_expand:n { \exp_not:n { ~ \abc \foo } } }
+    \tl_show:x { \text_expand:n { \tl_tail:n { ~ \abc \foo } } }
+  }
+
 \END
diff --git a/l3kernel/testfiles/m3text001.tlg b/l3kernel/testfiles/m3text001.tlg
@@ -51,3 +51,13 @@ l. ...  }
 <recently read> }
 l. ...  }
 ============================================================
+============================================================
+TEST 8: Expansion noexpand
+============================================================
+>  \abc \foo .
+<recently read> }
+l. ...  }
+> \foo .
+<recently read> }
+l. ...  }
+============================================================