[jamming] Path specification (was: Majam - keeping jamup-to-date)

[Eduard de Jong]

At 09:12 +0200 14-08-2006, Johan Nilsson wrote:
>  >  Here is a two part solution:
>>
>>  1. Define a portable path format for use in jam, jambase and
>  > jamfile's on all platforms.
In Java a file name is represented in a canonical form, that is with 
a '/' as component separator. We may look at their solution to 
cross-platform file names.

>  >
>>  2. Add two modifiers, similar to what Alen has adopted, one
>>  for converting native into portable ':~' and one to convert
>>  from portable to native ':/'
>
>I'd prefer something like the T/F modifiers suggested by David Turner
>(or why not N(ative)/P(ortable - if they aren't already used).

Maybe we do need modifiers at all, and jam can be smart enough to do it for us
--input--
When jam, interprets a string constant value it performs a scan to 
see if it contains a file name. This scan is specific for the 
platform that executes jam for variable assignments on the command 
line, from the environment, the result of GLOB and of the result of 
binding. File name constants in Jamfiles are scanned as 'canonical'. 
In all cases the internal representation in memeory of the value is 
'canonical.
--output--
When a variable is expanded in an action body any of its elements 
that represent file names are converted to the platform that executes 
the actions.

In order to get there the internal variable definition needs to 
include a marker that indicates if it is a file name or not.


>
>>
>>
>>   Based on my quick reading of the OpenVMS links provided by
>>  John and Tim a portable path could be defined as follows:
>>
>>  Absolute path:
>>  "drive:/subpath1/subpath2/file.ext;v"
>>   where drive: and ;v optional, leading / mandatory
>>
>>  Relative path:
>>  "../subpath/file.ext;v"
>>   where ;v optional, leading non-/ mandatory
>
>Well, for portable paths, I'd prefer a leading / for absolute paths and
>to get rid of the version altogether, i.e.:

There are other components to consider as part of a file name in the 
canonical representation, like the member of an archive or library. 
For instance, in Java an '!' is used to separate the archive file 
name from the archive member file name, which is also a path name.


So what is needed is a 'canonical file name syntax' that contains all 
possible components we may wish to recognize and store&process during 
execution.

This 'canonical' syntax is to be used in jamfiles. Any non portable 
components present in the syntax are highly unlikely to be present in 
portable jamfiles, so the jamfile writer can resort to the subset of 
the canonical syntax that is portable.

And, for any of these canonical file name components there is a 
:modifier to retrieve or change it. If they are not present in jam 
files, the non-portable components of a file name will only emerge 
during execution.

We only need one new modifiers :V for the version, and a process rule 
that prohibits the version from being propagated when any component 
is retrieved or modified. This will guarantee that the version is 
only attached to the original file name, and not to any of its 
derivations. A similar rule should apply to archive members.

>
>Absolute path:
>"/drive:/subpath1/subpath2/file.ext"
>
>Relative path:
>"subpath/file.ext"

A canonical syntax could be:
[[rootname]:][<dirpath>/]filename[.ext]*[$version][:[memberpath/]memberfilename[.ext]]

Where any component except the filename is optional, and, provided 
that the filename and at least one other component are present, a 
string in this format can be uniquely recognized as a file name.

With this syntax an absolute path in the canonical representation is 
a string  starting with a ':'.

And, in this syntax there is the 'hint' that the root of an archive 
member is the name of the archive file...

>
>Globbing should always return portable paths on all platforms (version
>stripped under VMS).

Exactly.

>
>/ Johan


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Eduard de Jong
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