Re: ✘Dia broken by 7075ba10648296389c193ed835112b0c920e5335

[Fred Wright]

On Sun, 3 Jan 2021, Gary E. Miller wrote:
> Yo Fred!
>
> You made all tergets of Utility() to be Pseudo(), but that is not
> always true.  It leads to this error when using dia:
>
> [...]
> chmod -w gpsd-3.21.1~dev/www/hacking.html
> Creating 'gpsd-3.21.1~dev/www/index.html'
> chmod -w gpsd-3.21.1~dev/www/index.html
> Creating 'gpsd-3.21.1~dev/www/troubleshooting.html'
> chmod -w gpsd-3.21.1~dev/www/troubleshooting.html
> cd gpsd-3.21.1~dev; dia -e www/cycle.svg www/cycle.dia
> No protocol specified
> www/cycle.dia --> www/cycle.svg
>
> scons: *** Pseudo target gpsd-3.21.1~dev/www/cycle.svg must not exist
> File "/usr/lib/python3.9/site-packages/SCons/Node/__init__.py", line 804, in 
> built
>
> Git has a copy of cycle.svg, built by dia from cycle.dia, because most
> users to not have dia installed.

Sorry - that went unnoticed since I didn't have 'dia' installed here.

Utility() was intended for "named procedures" which are always aliases, so 
it's not the proper choice for a file target, though it didn't generate 
any complaints in such cases until Pseudo() was added.  This seems to be 
the only use of Utility() for a file target, where plain old Command() is 
the proper choice, and seems to be working so far (after installing 
'dia').

I don't think it makes sense to include an Alias() for it, since that only 
matters when using that specific file as a target on the command line, 
where needing to prefix it with the variantdir is no different than any of 
the other build products (which may or may not be worth fixing).  The 
normal Utility() targets aren't files at all, so having to prefix them 
with variantdir was a silliness that was inconsistently fixed.

I see no reason to apply Precious() to cycle.svg, given the way it's 
built.  It also seems that Precious() is utterly pointless for a non-file 
target, so the comment in Utility() is quite correct in questioning it. 
:-)

The commit that originally introduced Pseudo() didn't explain what 
misbehavior it was fixing, though I had to disable it for SCons 2.3.0, 
where it doesn't exist.  The limited documentation on Pseudo() explains 
*when* one might use it, but not *why*.

Fred Wright