* src/lread.c (infile): Set/reset it like a dynamically scoped variable

I've seen segfaults where `infile` is nil when we get to
readbyte_from_file, presumably because Fload set it to NULL (via
close_infile_unwind) just before returning to its caller which was
probably itself within another read/load and for some reason
readevalloop didn't get to re-set `infile` like it used to do at every
iteration.  I was not able to really track down the bug, but the way
`infile` was set/reset seemed fragile and managing it like a standard
dynamically-scoped var seems both safer (and more efficient since we
don't need readevalloop to constantly re-set it).

(readchar): Assert that `infile` is set if using a function the depends on it.
(readbyte_from_file): Assert that `infile` is set.
(close_infile_unwind): Reset `infile` to its previous value rather than
to NULL.
(Fload): Remember the previous value of `infile` before chaning it.
(readevalloop): Don't set `infile` any more.

1 files changed, 11 insertions, 6 deletions

diff --git a/src/lread.c b/src/lread.c
index eecb5e141df..23e4616b6f8 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -287,6 +287,7 @@ readchar (Lisp_Object readcharfun, bool *multibyte)
 
   if (EQ (readcharfun, Qget_file_char))
     {
+      eassert (infile);
       readbyte = readbyte_from_file;
       goto read_multibyte;
     }
@@ -320,6 +321,7 @@ readchar (Lisp_Object readcharfun, bool *multibyte)
          string, and the cdr part is a value of readcharfun given to
          read_vector.  */
       readbyte = readbyte_from_string;
+      eassert (infile);
       if (EQ (XCDR (readcharfun), Qget_emacs_mule_file_char))
         emacs_mule_encoding = 1;
       goto read_multibyte;
@@ -328,6 +330,7 @@ readchar (Lisp_Object readcharfun, bool *multibyte)
   if (EQ (readcharfun, Qget_emacs_mule_file_char))
     {
       readbyte = readbyte_from_file;
+      eassert (infile);
       emacs_mule_encoding = 1;
       goto read_multibyte;
     }
@@ -506,6 +509,7 @@ readbyte_from_stdio (void)
 static int
 readbyte_from_file (int c, Lisp_Object readcharfun)
 {
+  eassert (infile);
   if (c >= 0)
     {
       eassert (infile->lookahead < sizeof infile->buf);
@@ -1078,10 +1082,11 @@ suffix_p (Lisp_Object string, const char *suffix)
 static void
 close_infile_unwind (void *arg)
 {
-  FILE *stream = arg;
-  eassert (infile == NULL || infile->stream == stream);
-  infile = NULL;
-  fclose (stream);
+  struct infile *prev_infile = arg;
+  fprintf (stderr, "Closing infile: back to %x!\n", prev_infile);
+  eassert (infile);
+  fclose (infile->stream);
+  infile = prev_infile;
 }
 
 DEFUN ("load", Fload, Sload, 1, 5, 0,
@@ -1413,7 +1418,7 @@ Return t if the file exists and loads successfully.  */)
     {
       if (! stream)
         report_file_error ("Opening stdio stream", file);
-      set_unwind_protect_ptr (fd_index, close_infile_unwind, stream);
+      set_unwind_protect_ptr (fd_index, close_infile_unwind, infile);
     }
 
   if (! NILP (Vpurify_flag))
@@ -2019,7 +2024,7 @@ readevalloop (Lisp_Object readcharfun,
       if (b && first_sexp)
         whole_buffer = (BUF_PT (b) == BUF_BEG (b) && BUF_ZV (b) == BUF_Z (b));
 
-      infile = infile0;
+      eassert (!infile0 || infile == infile0);
     read_next:
       c = READCHAR;
       if (c == ';')