bug#68546: 29.1.90; end-of-file has incorrect data when signaled within a load

[Spencer Baugh]

Stefan Monnier <monnier@iro.umontreal.ca> writes:
>>    xsignal0 (Qend_of_file);
>>  }
>> @@ -2434,6 +2434,8 @@ readevalloop (Lisp_Object readcharfun,
>>    while (continue_reading_p)
>>      {
>>        specpdl_ref count1 = SPECPDL_INDEX ();
>> +      if (NILP (Vread_end_of_file_data))
>> +        specbind (Qread_end_of_file_name, Vload_true_file_name);
>
> Why the `if` condition here?  Sounds like it could lead to problems for
> nested loads and such.

Good point.

Actually, a good enough point that I completely reworked the patch in
response to it.  We don't need to add a new dynamically scoped variable
at all: we can just pass readcharfun to end_of_file_error and check
that.  Much simpler.

This should solve the original bug; while I'm here, I also added a
BUFFERP check, so that read on a buffer will signal end-of-file with the
buffer as data instead of just nil.

I tried including the line number and column number as data in the
BUFFERP case, but it seemed a bit noisy, since it's only useful in the
case where the buffer is narrowed (otherwise the error is just obviously
at the end of the buffer).

>From 03e06a591896ed85f3c38908a0b3105b8bafc945 Mon Sep 17 00:00:00 2001
From: Spencer Baugh <sbaugh@janestreet.com>
Date: Tue, 8 Apr 2025 17:13:08 -0400
Subject: [PATCH] Signal end-of-file with more correct data

end_of_file_error previously always signaled end-of-file with
load-true-file-name if that was non-nil (and a string).
However, this might be the wrong thing to do; for example, if a
file being loaded calls read on a buffer.

We can determine what's correct by also checking if readcharfun
is reading from a file.  Also, by checking that we can signal a
better error for read on a buffer.

* src/lread.c (end_of_file_error): Check readcharfun to
determine what data to signal with.  (bug#68546)
(read_char_escape, read_char_literal, read_string_literal)
(skip_space_and_comments, read0): Pass readcharfun to
end_of_file_error.
---
 src/lread.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/lread.c b/src/lread.c
index d39330bd0eb..2f18d763b9c 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -2342,12 +2342,14 @@ readevalloop_1 (int old)
    information.  */
 
 static AVOID
-end_of_file_error (void)
+end_of_file_error (Lisp_Object readcharfun)
 {
-  if (STRINGP (Vload_true_file_name))
+  if (FROM_FILE_P (readcharfun) && STRINGP (Vload_true_file_name))
     xsignal1 (Qend_of_file, Vload_true_file_name);
-
-  xsignal0 (Qend_of_file);
+  else if (BUFFERP (readcharfun))
+    xsignal1 (Qend_of_file, readcharfun);
+  else
+    xsignal0 (Qend_of_file);
 }
 
 static Lisp_Object
@@ -2858,7 +2860,7 @@ read_char_escape (Lisp_Object readcharfun, int next_char)
   switch (c)
     {
     case -1:
-      end_of_file_error ();
+      end_of_file_error (readcharfun);
 
     case 'a': chr = '\a'; break;
     case 'b': chr = '\b'; break;
@@ -3031,7 +3033,7 @@ read_char_escape (Lisp_Object readcharfun, int next_char)
           {
             int c = READCHAR;
             if (c < 0)
-              end_of_file_error ();
+              end_of_file_error (readcharfun);
             if (c == '}')
               break;
             if (c >= 0x80)
@@ -3201,7 +3203,7 @@ read_char_literal (Lisp_Object readcharfun)
 {
   int ch = READCHAR;
   if (ch < 0)
-    end_of_file_error ();
+    end_of_file_error (readcharfun);
 
   /* Accept `single space' syntax like (list ? x) where the
      whitespace character is SPC or TAB.
@@ -3347,7 +3349,7 @@ read_string_literal (Lisp_Object readcharfun)
     }
 
   if (ch < 0)
-    end_of_file_error ();
+    end_of_file_error (readcharfun);
 
   if (!force_multibyte && force_singlebyte)
     {
@@ -3777,7 +3779,7 @@ skip_space_and_comments (Lisp_Object readcharfun)
          c = READCHAR;
        while (c >= 0 && c != '\n');
       if (c < 0)
-       end_of_file_error ();
+       end_of_file_error (readcharfun);
     }
   while (c <= 32 || c == NO_BREAK_SPACE);
   UNREAD (c);
@@ -3972,7 +3974,7 @@ read0 (Lisp_Object readcharfun, bool locate_syms)
   bool multibyte;
   int c = READCHAR_REPORT_MULTIBYTE (&multibyte);
   if (c < 0)
-    end_of_file_error ();
+    end_of_file_error (readcharfun);
 
   switch (c)
     {
@@ -4403,7 +4405,7 @@ read0 (Lisp_Object readcharfun, bool locate_syms)
              {
                c = READCHAR;
                if (c < 0)
-                 end_of_file_error ();
+                 end_of_file_error (readcharfun);
                quoted = true;
              }
 
-- 
2.39.3