TIP 637: Make [glob] always -nocomplain

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Bounty program for improvements to Tcl and certain Tcl packages.
Author:         Don Porter <[email protected]>
State:          Draft
Type:           Project
Vote:           Pending
Created:        17-Sep-2022
Tcl-Version:    9.0
Tcl-Branch:	novem

Abstract

This TIP proposes revising the behavior of [glob] to return an empty list without error when no matches are found.

Background

When [glob] finds zero matching files, it raises an error.

% glob noSuchFile
no files matched glob pattern "noSuchFile"

This is unfortunate because when using [glob], finding zero matches is no more an indication of error than finding one or finding 42. Using [catch] to deal with this misfeature was an annoying burden, and in the days before [try] and a strong deployment of --errorcode values, it was burdensome to distinguish the caught circumstance of zero matches from true error conditions like a file system failure, or a syntax error in argument substitution.

The -nocomplain option was added to [glob] long ago. It was in place at least by Tcl 8.0. When present, this option disables the treatment of any empty result as an error.

% glob -nocomplain noSuchFile
%

With this option, the [glob] command could be used more effectively and robustly.

In hindsight, [glob -nocomplain] is the better primitive, and should have been the original behavior of the command. For a new major release, [glob] can become what it should have been in the first place.

Specification

Revise [glob] so that it does not raise an error when no matches are found.

Keep accepting -nocomplain as an option, but it has no effect.

Compatibility

The only compatibility issue is with any programmer who wants [glob] to raise an error when no matches are found. It is believed this will be a very uncommon desire.

Such a programmer can create a proc to post-process an empty list returned by [glob] into an error. Tcl namespaces then allow the programmer to favor his proc over the built-in command, or even to replace the built-in with it when circumstances make that sensible.

Reference Implementation

This change has long been implemented in the novem branch, and should not be difficult to extract and apply.

Copyright

This document has been placed in the public domain.