Allow text before but not after \end{foo} for f-type env

latex3 · Jan 8, 2025 · 2391636 · 2391636
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diff --git a/base/doc/usrguide.tex b/base/doc/usrguide.tex
@@ -888,6 +888,13 @@ \subsection{Verbatim environments}
 at both ends of the body. Putting the prefix |!| before \texttt{f} suppresses
 space-trimming.
 
+Collection of the body takes place on a line-by-line basis: content is
+collected up to the end-of-line in the source, then examined before storage.
+This means that the line ending the environment (containing in the example
+above |\end{MyVerbatim}|) cannot have any text \emph{after} the end of the
+environment. Text \emph{before} the end of environment is treated normally,
+but note that there is no trailing \cs{obeyedline} added if there is text here.
+
 Notice that for technical reasons, we recommend that an optional argument
 coming immediately before an \texttt{f} specification should not allow any
 spaces, achieved by adding the \texttt{!} as showing in the example. However,

diff --git a/base/ltcmd.dtx b/base/ltcmd.dtx
@@ -3483,8 +3483,12 @@
 \cs_new_protected:Npn \@@_grab_f_loop:w { }
 \cs_new_protected:Npn \@@_grab_f_end:nn #1#2
   {
-      \tl_if_blank:nF {#1#2}
-        \ERROR
+      \tl_put_right:Nn \l_@@_v_arg_tl {#1}
+      \tl_if_blank:nF {#2}
+        {
+          \msg_warning:nnee { cmd } { chars-dropped-last-line } { \exp_not:n {#2} }
+            { \exp_not:V \@currenvir }
+        }
     \exp_args:NNNo \group_end:
     \tl_set:Nn \l_@@_v_arg_tl { \l_@@_v_arg_tl }
     \@@_add_arg:x
@@ -4969,6 +4973,15 @@
     with~a~command~that~was~never~defined.
     \c_@@_ignore_def_tl
   }
+%    \end{macrocode}
+% \changes{v1.3a}{2025-01-08}{New message \texttt{chars-dropped-last-line}}
+%    \begin{macrocode}
+\msg_new:nnnn { cmd } { chars-dropped-last-line }
+  { Characters~'#1'~dropped~after~end~of~#2~environment. }
+  {
+    LaTeX~was~collecting~a~verbatim-like~environment,~and~the~characters~
+    '#1'~were~found~after~\end{#2}~on~the~last~line:~this~is~not~supported.
+  }
 \msg_new:nnnn { cmd } { env-already-defined }
   { Environment~'#1'~already~defined. }
   {

diff --git a/base/testfiles-ltcmd/ltcmd009.lvt b/base/testfiles-ltcmd/ltcmd009.lvt
@@ -135,4 +135,22 @@
 
 \ENDTEST
 
+\BEGINTEST { Verbatim~body~collection~last~line~handling }
+
+\ExplSyntaxOn
+\NewDocumentEnvironment { env9 } { f }
+  { \TYPE { \tl_to_str:n {|#1|} } }
+  { }
+\ExplSyntaxOff
+
+\begin{env9}
+  Content
+text \end{env9}
+
+\begin{env9}
+  Content
+\end{env9} more test
+
+\ENDTEST
+
 \END
diff --git a/base/testfiles-ltcmd/ltcmd009.tlg b/base/testfiles-ltcmd/ltcmd009.tlg
@@ -57,3 +57,10 @@ TEST 3: Verbatim body collection
 |...|\obeyedline   Content\obeyedline   &\^|
 |...|\obeyedline   Content\obeyedline   &\^|
 ============================================================
+============================================================
+TEST 4: Verbatim body collection last line handling
+============================================================
+|  Content\obeyedline text |
+LaTeX cmd Warning: Characters ' more test' dropped after end of env9 environment.
+|  Content|
+============================================================