Alias expansion madness contd.

[Peter Stephenson <pws@xxxxxx>]

There's quite a sizeable bug in the code I posted last week (now in
3.0.2-test1) to improve handling of where aliases are marked as no
longer in use:  if alias text ends at the same point as a new alias
expansion, everything goes pear-shaped (e.g. `alias foo=echo bar=foo':
bar will not be recognised after the first time it's used).

The problem was I'd forgotten about the possibility of popping more
than one alias at the same place, and hence the need to keep all those
ready for re-pushing them on the alias stack during an inungetc().
Obviously the old mechanism wasn't as stupid as I thought.

The previous patch stands, however, and I've fixed the problem by
saving more information on the input stack which will allow the latter
to be incremented back to its old position to re-access sets of
aliases.  The actual rigmarole gone through when a set of alias
expansions terminate at the same point is pretty hair-raising, but I
can't think of a better way of making the handling of aliases' in-use
status invisible to the rest of the code:  you've got to be prepared
to pop and later re-push arbitrary numbers of aliases on/off the alias
stack.

On the other hand, now I've bitten the bullet and stored the alias in
the input stack itself, it should be possible to eliminate the alias
stack and simply use the input stack.  I'll look into this.

*** Src/input.c.pop2	Mon Dec  9 10:04:54 1996
--- Src/input.c	Mon Dec  9 13:54:50 1996
***************
*** 57,69 ****
   *
   * PWS 1995/06/30
   * 
!  * 1996/11/02: The INP_ALIAS flag is now attached to the line pushed onto
   * the stack, rather than the line which replaces it.  After the line is
   * popped, the alias is popped from alstack when starting to read it, or
   * if the line is discarded, and recorded as inalias.  The INP_ALPOP
   * flag indicates that this has already happened.  If the line is
   * inungetc()'d back to the previous point, inbufpush, the alias is
   * pushed again.  None of this is visible to the calling code.
   */
  
  #include "zsh.h"
--- 57,73 ----
   *
   * PWS 1995/06/30
   * 
!  * 1996/12/02: The INP_ALIAS flag is now attached to the line pushed onto
   * the stack, rather than the line which replaces it.  After the line is
   * popped, the alias is popped from alstack when starting to read it, or
   * if the line is discarded, and recorded as inalias.  The INP_ALPOP
   * flag indicates that this has already happened.  If the line is
   * inungetc()'d back to the previous point, inbufpush, the alias is
   * pushed again.  None of this is visible to the calling code.
+  *
+  * 1996/12/09 The alias being expanded is now saved on the input stack, too.
+  * The stack can be incremented back to its old value to allow multiple
+  * aliases popped from the alias stack at the same point to be re-pushed.
   */
  
  #include "zsh.h"
***************
*** 72,78 ****
  static char *inbuf;		/* Current input buffer */
  static char *inbufptr;		/* Pointer into input buffer */
  static char *inbufpush;		/* Character at which to re-push alias */
- static Alias inalias;		/* Alias to be popped at start of read */
  static int inbufleft;		/* Characters left in current input
  				   stack element */
  static int inbufflags;		/* flags: see INP_* in zsh.h  */
--- 76,81 ----
***************
*** 86,91 ****
--- 89,95 ----
  
  struct instacks {
      char *buf, *bufptr;
+     Alias alias;
      int bufleft, bufct, flags;
  };
  static struct instacks *instack, *instacktop;
***************
*** 155,160 ****
--- 159,165 ----
  inpopalias(void)
  {
      char *t;
+     Alias inalias;
  
      if (!alstackind || inbufflags & INP_ALPOP)
  	return;
***************
*** 374,382 ****
  	 * Note this may be a dummy (history expansion) entry.
  	 */
  	if (inbufptr == inbufpush && inbufflags & INP_ALPOP) {
! 	    if ((alstack[alstackind++] = inalias))
! 		inalias->inuse = 1;
! 	    inbufflags &= ~INP_ALPOP;
  	}
      }
  }
--- 379,396 ----
  	 * Note this may be a dummy (history expansion) entry.
  	 */
  	if (inbufptr == inbufpush && inbufflags & INP_ALPOP) {
! 	    /*
! 	     * Go back up the stack over all entries which were alias
! 	     * expansions and were pushed with nothing remaining to read.
! 	     */
! 	    do {
! 		if ((alstack[alstackind++] = instacktop->alias))
! 		    instacktop->alias->inuse = 1;
! 		instacktop++;
! 	    } while ((instacktop->flags & INP_ALIAS) && !instacktop->bufleft);
! 	    inbufflags = INP_CONT;
! 	    inbufleft = 0;
! 	    inbuf = inbufptr = "";
  	}
      }
  }
***************
*** 438,451 ****
  	/* Initial stack allocation */
  	instack = (struct instacks *)zalloc(instacksz*sizeof(struct instacks));
  	instacktop = instack;
-     } else if (instacktop == instack + instacksz) {
- 	/* Expand the stack */
- 	instack = (struct instacks *)
- 	    realloc(instack,
- 		    (instacksz + INSTACK_EXPAND)*sizeof(struct instacks));
- 	instacktop = instack + instacksz;
- 	instacksz += INSTACK_EXPAND;
      }
      instacktop->buf = inbuf;
      instacktop->bufptr = inbufptr;
      instacktop->bufleft = inbufleft;
--- 452,459 ----
  	/* Initial stack allocation */
  	instack = (struct instacks *)zalloc(instacksz*sizeof(struct instacks));
  	instacktop = instack;
      }
+ 
      instacktop->buf = inbuf;
      instacktop->bufptr = inbufptr;
      instacktop->bufleft = inbufleft;
***************
*** 454,467 ****
      if (flags & INP_ALIAS && alstackind) {
  	flags = (flags & ~INP_ALIAS) | INP_CONT;
  	instacktop->flags = inbufflags | INP_ALIAS;
      } else {
  	instacktop->flags = inbufflags;
      }
  
      instacktop++;
  
      inbufpush = inbuf = NULL;
-     inalias = NULL;
  
      inputsetline(str, flags);
  }
--- 462,488 ----
      if (flags & INP_ALIAS && alstackind) {
  	flags = (flags & ~INP_ALIAS) | INP_CONT;
  	instacktop->flags = inbufflags | INP_ALIAS;
+ 	instacktop->alias = alstack[alstackind-1];
      } else {
  	instacktop->flags = inbufflags;
      }
  
      instacktop++;
+     if (instacktop == instack + instacksz) {
+ 	/* Expand the stack */
+ 	instack = (struct instacks *)
+ 	    realloc(instack,
+ 		    (instacksz + INSTACK_EXPAND)*sizeof(struct instacks));
+ 	instacktop = instack + instacksz;
+ 	instacksz += INSTACK_EXPAND;
+     }
+     /*
+      * We maintain the entry above the highest one with real
+      * text as a flag to inungetc() that it can stop re-pushing the stack.
+      */
+     instacktop->flags = 0;
  
      inbufpush = inbuf = NULL;
  
      inputsetline(str, flags);
  }

-- 
Peter Stephenson <pws@xxxxxx>       Tel: +49 33762 77366
WWW:  http://www.ifh.de/~pws/       Fax: +49 33762 77413
Deutches Electronen-Synchrotron --- Institut fuer Hochenergiephysik Zeuthen
DESY-IfH, 15735 Zeuthen, Germany.