[BUG] functions can't create global readonly variables

[BUG] functions can't create global readonly variables

[Martijn Dekker]

It is apparently impossible to create global readonly variables from
within a function.

If a variable is created with a command like
    readonly var=value
then the entire variable gets a function-local scope, as if 'local' were
used.

If a global variable is set first, then set to readonly with 'readonly'
or 'typeset -r', then the read-only attribute only lasts within the
function, and the global variable remains read/write.

I don't know if this is intended behaviour for native zsh mode; the
'zshbuiltins' man page does not mention anything about this. But it is
certainly a bug for POSIX/'emulate sh' mode.

Steps to reproduce:

$ fn() { readonly var=foo; var=bar; }
$ fn
fn: read-only variable: var
$ echo $var

$ var=writtento
$ echo $var
writtento
$ fn() { var=foo; readonly var; var=bar; }
$ fn
fn: read-only variable: var
$ echo $var
foo
$ var=writtento
$ echo $var
writtento

Confirmed in zsh 4.1.1 through current.

Thanks,

- Martijn

Re: [BUG] functions can't create global readonly variables

[Bart Schaefer]

On Jan 2,  4:27am, Martijn Dekker wrote:
}
} It is apparently impossible to create global readonly variables from
} within a function.

    typeset -gr var=value
or
    readonly -g var=value

} I don't know if this is intended behaviour for native zsh mode; the
} 'zshbuiltins' man page does not mention anything about this.

Of course it does:

    readonly
	 Same as typeset -r.

    typeset ...
	 Set or display attributes and values for shell parameters.

	 A parameter is created for each NAME that does not already refer
	 to one.  When inside a function, a new parameter is created for
	 every NAME (even those that already exist), and is unset again
	 when the function completes.

} But it is certainly a bug for POSIX/'emulate sh' mode.

I think it's undefined behavior for POSIX/'emulate sh'.  Certainly bash
agrees with us:

$ foo() { typeset -r bar; typeset -p bar; }
$ foo
declare -r bar
$ typeset -p bar
bash: typeset: bar: not found

Re: [BUG] functions can't create global readonly variables

[Peter Stephenson]

On Fri, 1 Jan 2016 20:27:10 -0800
Bart Schaefer <schaefer@brasslantern.com> wrote:
> I think it's undefined behavior for POSIX/'emulate sh'.  Certainly bash
> agrees with us:
> 
> $ foo() { typeset -r bar; typeset -p bar; }
> $ foo
> declare -r bar
> $ typeset -p bar
> bash: typeset: bar: not found

Bash is treating "typeset -r bar" differently from "readonly bar".
"readonly" affects any existing parameter or creates its own.
I think readonly is equivalent to "typeset -rg", so it stomps
on any existing global, too (unless it was already readonly).

We could make this optional behaviour for compatibility, possibly with
POSIX_BUILTINS which is a real ragbag of POSIX funnies.

pws

Re: [BUG] functions can't create global readonly variables

[Bart Schaefer]

On Jan 2,  6:18pm, Peter Stephenson wrote:
} 
} I think readonly is equivalent to "typeset -rg", so it stomps
} on any existing global, too (unless it was already readonly).
} 
} We could make this optional behaviour for compatibility, possibly with
} POSIX_BUILTINS which is a real ragbag of POSIX funnies.

Yes, this seems like a job for POSIX_BUILTINS.

I would note that even with -g there is no way to create an actual global
variable in the event that some intervening function has declared a name
to be local.

BIN_EXPORT was defined but never used, so ...

What additional test case should we have?


diff --git a/Doc/Zsh/builtins.yo b/Doc/Zsh/builtins.yo
index dc0b947..fb630a7 100644
--- a/Doc/Zsh/builtins.yo
+++ b/Doc/Zsh/builtins.yo
@@ -1465,7 +1465,10 @@ cancels both tt(-p) and tt(-u).
 The tt(-c) or tt(-l) flags cancel any and all of tt(-kpquz).
 )
 cindex(parameters, marking readonly)
-alias(readonly)(typeset -r)
+item(tt(readonly))(
+Same as tt(typeset -r).  With the tt(POSIX_BUILTINS) option set, same
+as tt(typeset -gr).
+)
 alias(rehash)(hash -r)
 findex(return)
 cindex(functions, returning from)
diff --git a/Src/builtin.c b/Src/builtin.c
index 05907f1..557487c 100644
--- a/Src/builtin.c
+++ b/Src/builtin.c
@@ -62,7 +62,7 @@ static struct builtin builtins[] =
     BUILTIN("enable", 0, bin_enable, 0, -1, BIN_ENABLE, "afmprs", NULL),
     BUILTIN("eval", BINF_PSPECIAL, bin_eval, 0, -1, BIN_EVAL, NULL, NULL),
     BUILTIN("exit", BINF_PSPECIAL, bin_break, 0, 1, BIN_EXIT, NULL, NULL),
-    BUILTIN("export", BINF_PLUSOPTS | BINF_MAGICEQUALS | BINF_PSPECIAL | BINF_ASSIGN, (HandlerFunc)bin_typeset, 0, -1, BIN_EXPORT, "E:%F:%HL:%R:%TUZ:%afhi:%lprtu", "xg"),
+    BUILTIN("export", BINF_PLUSOPTS | BINF_MAGICEQUALS | BINF_PSPECIAL | BINF_ASSIGN, (HandlerFunc)bin_typeset, 0, -1, 0, "E:%F:%HL:%R:%TUZ:%afhi:%lprtu", "xg"),
     BUILTIN("false", 0, bin_false, 0, -1, 0, NULL, NULL),
     /*
      * We used to behave as if the argument to -e was optional.
@@ -106,7 +106,7 @@ static struct builtin builtins[] =
     BUILTIN("pwd", 0, bin_pwd, 0, 0, 0, "rLP", NULL),
     BUILTIN("r", 0, bin_fc, 0, -1, BIN_R, "IlLnr", NULL),
     BUILTIN("read", 0, bin_read, 0, -1, 0, "cd:ek:%lnpqrst:%zu:AE", NULL),
-    BUILTIN("readonly", BINF_PLUSOPTS | BINF_MAGICEQUALS | BINF_PSPECIAL | BINF_ASSIGN, (HandlerFunc)bin_typeset, 0, -1, 0, "AE:%F:%HL:%R:%TUZ:%afghi:%lptux", "r"),
+    BUILTIN("readonly", BINF_PLUSOPTS | BINF_MAGICEQUALS | BINF_PSPECIAL | BINF_ASSIGN, (HandlerFunc)bin_typeset, 0, -1, BIN_READONLY, "AE:%F:%HL:%R:%TUZ:%afghi:%lptux", "r"),
     BUILTIN("rehash", 0, bin_hash, 0, 0, 0, "df", "r"),
     BUILTIN("return", BINF_PSPECIAL, bin_break, 0, 1, BIN_RETURN, NULL, NULL),
     BUILTIN("set", BINF_PSPECIAL | BINF_HANDLES_OPTS, bin_set, 0, -1, 0, NULL, NULL),
@@ -2533,6 +2533,10 @@ bin_typeset(char *name, char **argv, LinkList assigns, Options ops, int func)
     if (OPT_ISSET(ops,'f'))
 	return bin_functions(name, argv, ops, func);
 
+    /* POSIX handles "readonly" specially */
+    if (func == BIN_READONLY && isset(POSIXBUILTINS) && !OPT_PLUS(ops, 'g'))
+	ops->ind['g'] = 1;
+
     /* Translate the options into PM_* flags.   *
      * Unfortunately, this depends on the order *
      * these flags are defined in zsh.h         */
diff --git a/Src/hashtable.h b/Src/hashtable.h
index b6346bb..3606e97 100644
--- a/Src/hashtable.h
+++ b/Src/hashtable.h
@@ -53,7 +53,7 @@
 #define BIN_LOGOUT   19
 #define BIN_TEST     20
 #define BIN_BRACKET  21
-#define BIN_EXPORT   22
+#define BIN_READONLY 22
 #define BIN_ECHO     23
 #define BIN_DISABLE  24
 #define BIN_ENABLE   25
diff --git a/Test/B02typeset.ztst b/Test/B02typeset.ztst
index 7d65cc8..681fe73 100644
--- a/Test/B02typeset.ztst
+++ b/Test/B02typeset.ztst
@@ -479,12 +479,12 @@
    setopt POSIXBUILTINS
    readonly pbro
    print ${+pbro} >&2
-   (typeset pbro=3)
+   (typeset -g pbro=3)
    (pbro=4)
-   readonly -p | grep pbro >&2  # shows up as "readonly" although unset
-   typeset -r pbro        # idempotent (no error)...
+   readonly -p pbro >&2   # shows up as "readonly" although unset
+   typeset -gr pbro       # idempotent (no error)...
    print ${+pbro} >&2     # ...so still readonly...
-   typeset +r pbro        # ...can't turn it off
+   typeset -g +r pbro     # ...can't turn it off
  )
 1:readonly with POSIX_BUILTINS
 ?0

Re: [BUG] functions can't create global readonly variables

[Peter Stephenson]

By the way it seems that, in bash at least, "readonly" breaks
encapsulation:

$ readonly foo=empty
$ fn() { local foo=bar; echo $foo; }
$ fn
bash: local: foo: readonly variable
empty

The only use I can see of this is for exported variables, where you
might want to ensure a specific value was always exported to an external
programme.

pws

Re: [BUG] functions can't create global readonly variables

[Bart Schaefer]

On Jan 3,  7:00pm, Peter Stephenson wrote:
}
} $ readonly foo=empty
} $ fn() { local foo=bar; echo $foo; }
} $ fn
} bash: local: foo: readonly variable
} empty

I suppose if you consider locality to be a property of the variable,
then making the variable readonly means you can't change that property.

Fortunately readonly in a nested function, where the name is declared
local in the outer function, does work like zsh's "typeset -gr" and
does not force the readonly into truly global scope.

Re: [BUG] functions can't create global readonly variables

[Martijn Dekker]

Bart Schaefer schreef op 02-01-16 om 05:27:
> On Jan 2,  4:27am, Martijn Dekker wrote:
> } I don't know if this is intended behaviour for native zsh mode; the
> } 'zshbuiltins' man page does not mention anything about this.
> 
> Of course it does:

I blame insufficient caffeination at the time of writing.

> } But it is certainly a bug for POSIX/'emulate sh' mode.
> 
> I think it's undefined behavior for POSIX/'emulate sh'.  Certainly bash
> agrees with us:
> 
> $ foo() { typeset -r bar; typeset -p bar; }
> $ foo
> declare -r bar
> $ typeset -p bar
> bash: typeset: bar: not found

But 'typeset' is not POSIX. When using the POSIX 'readonly' special
builtin, bash acts like other POSIX shells and unlike zsh:

$ foo() { readonly bar=baz; typeset -p bar; }
$ foo
declare -r bar="baz"
$ typeset -p bar
declare -r bar="baz"

Thanks,

- M.