[Tcl-bugs] [ tcl-Feature Requests-1162286 ] RFE: invoke "package forget <pkg>" on errors

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Feature Requests item #1162286, was opened at 2005-03-12 22:59
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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=360894&aid=1162286&group_id=10894

Category: 38. Package Manager
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Hemang Lavana (hemanglavana)
Assigned to: Don Porter (dgp)
Summary: RFE: invoke "package forget <pkg>" on errors

Initial Comment:
Hi,

The documentation for "package" command recommends that
"package provide <pkg> <ver>" should be at the bottom
of the library. However, most users are not aware of
the problem that can occur if the "package provide" cmd
is at the top of the library. This is illustrated in
the following example:

hlavana-u5:138> cat foo.tcl 
# foo.tcl
package provide foo 0.9.1
proc foo args {puts "PRINT: foo"}
set a ;# syntax error: var a is not defined
hlavana-u5:139>
hlavana-u5:139> cat pkgIndex.tcl 
# pkgIndex.tcl
package ifneeded foo 0.9.1 [list source [file join $dir
foo.tcl]]
hlavana-u5:140>
hlavana-u5:140> cat run_foo.tcl 
# run_foo.tcl
catch {package require foo} out1
puts "First time=$out1"
catch {package require foo} out2
puts "Second time=$out2"
hlavana-u5:141>
hlavana-u5:141> tclsh run_foo.tcl 
First time=can't read "a": no such variable
Second time=0.9.1
hlavana-u5:142>

This example shows that a script might end up thinking
that the package foo has been loaded successfully even
though  there were errors in loading it.

Moreover, most users like to see the "package provide
.." command appear at the top of the library even after
I have explained this issue to them. Note that many of
the packages in tcllib module have the "package
provide" command at the top of the script.

To overcome these problems, I would like to request an
enhancement: whenever "package require ..." fails to
load correctly, it should internally invoke "package
forget <pkg>". 

This specific solution does have one side-effect
though: consider that package foo, version 0.9 has been
successfully loaded  and the script is trying to load
package foo, version 1.1. If foo1.1 is not found, then
blindly calling "package forget foo" will
unload(forget) foo0.9 as well which is not correct.

I hope this issue can be resolved in the tcl-core
instead of asking users to move "package provide"
command to the bottom of the library.

Hemang.




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