[PATCH] Re: zsh/db oddities

[Bart Schaefer <schaefer@brasslantern.com>]

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Returning to this 8+ months later ...

On Mon, Sep 6, 2021 at 9:29 PM Bart Schaefer <schaefer@brasslantern.com> wrote:
>
> Open a database as a global and assign something to it:
> [...]
> Now start messing with the declaration in a function:
> [...]
> As soon as the tied parameter is declared local, the file has been
> written, erasing all the existing values.  This seems undesirable?
> [...]
> Untying the local destroys the global, too, and leaves the file as the
> local wrote it.
> [...]
> I think the correct thing might be to prohibit changing the scope,
> similar to what happens when an attempt is made to remove the readonly
> attribute?
> [...]
> Re-ztie-ing the database file while it is still tied, is already
> handled as an error.

Looking into how this might be accomplished, I noticed this:

#ifndef PM_UPTODATE
#define PM_UPTODATE     (1<<19) /* Parameter has up-to-date data (e.g.
loaded from DB) */
#endif

I don't think that's a safe choice of bitflag any more?  That was
introduced 2017-02-16, but the PM_ bit values were rearranged
2018-10-12 and bit 19 is now PM_LOCAL.  That doesn't have any effect
on the aforementioned behavior of "local"/"zuntie", but perhaps
something like this is better?

-#ifndef PM_UPTODATE
-#define PM_UPTODATE     (1<<19) /* Parameter has up-to-date data
(e.g. loaded from DB) */
+#ifndef PM_UPTODATE /* Parameter has up-to-date data (e.g. loaded from DB) */
+#define PM_UPTODATE     PM_DONTIMPORT_SUID     /* Safe PM_ bit to re-use */
 #endif

Back on the original issue, the simplest way to fix this appears to be
to declare the ztie'd parameters to be PM_SINGLE.

% zmodload zsh/db/gdbm
ztie -d db/gdbm -f sample.gdbm sampledb
% () {
local sampledb
typeset +m sampledb
}
(anon):local:2: sampledb: can only have a single instance
%

Patch attached.  Comments welcome.

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diff --git a/Src/Modules/db_gdbm.c b/Src/Modules/db_gdbm.c
index 7e11ec939..3fefd412b 100644
--- a/Src/Modules/db_gdbm.c
+++ b/Src/Modules/db_gdbm.c
@@ -34,8 +34,8 @@
 #include "db_gdbm.mdh"
 #include "db_gdbm.pro"
 
-#ifndef PM_UPTODATE
-#define PM_UPTODATE     (1<<19) /* Parameter has up-to-date data (e.g. loaded from DB) */
+#ifndef PM_UPTODATE /* Parameter has up-to-date data (e.g. loaded from DB) */
+#define PM_UPTODATE     PM_DONTIMPORT_SUID	/* Safe PM_ bit to re-use */
 #endif
 
 static Param createhash( char *name, int flags );
@@ -111,7 +111,7 @@ bin_ztie(char *nam, char **args, Options ops, UNUSED(int func))
     struct gsu_scalar_ext *dbf_carrier;
     char *resource_name, *pmname;
     GDBM_FILE dbf = NULL;
-    int read_write = GDBM_SYNC, pmflags = PM_REMOVABLE;
+    int read_write = GDBM_SYNC, pmflags = PM_REMOVABLE|PM_SINGLE;
     Param tied_param;
 
     if(!OPT_ISSET(ops,'d')) {