ERROR: Key @PLAINNAME@ is not in the dictionary

[stsp]

Hi, I am trying to write this generator:

gtgen = generator(find_program(PD),
  arguments: ['@INPUT@', SRC / 'proto.h'],
  output: GEN_TMP['@PLAINNAME@'],
  capture: true)

And what I get, is:
../meson.build:76:18: ERROR: Key @PLAINNAME@ is not in the dictionary.
Why the key wasn't expanded before a
dictionary look-up?

[eli-schwartz]

Dictionaries are parsed by the interpreter first, since they are used as arguments to the function. The return value of the dictionary lookup is used as an input argument to the function.

This is how most programming languages work.

[eli-schwartz]

As a matter of curiosity, why do you want to use a different template for each output file? The purpose of a generator is to have a distinct input->output correspondence.

[stsp]

I am generating lots of unrelated files.
There is a shell script that generates
them by the number. I.e.
gen.sh 100 generates the file number
100 and dumps it to stdout, and the name
is assigned to it via dictionary.
This was done to improve parallel builds.
I can of course generate all files in 1 go.
But they go to entirely unrelated build
target chains, so I made them generated
on demand to not produce a stall point
for parallel builds.

[eli-schwartz]

A generator is very similar to a custom_target run inside of a foreach loop.

The generator sacrifices flexibility (you can't specify as many details) in order to be simpler to use (you don't have to specify as many details).

[stsp]

So what would you suggest?
Ideally, I'd like to be able to generate
many custom_target()s with a foreach loop. :)
But I don't suppose meson supports
such a meta-programming tricks.

So I am right that I only have 2 solutions
here: either copy/paste custom_target()s
and adjust each by hands, or generate all
files in 1 go, adding the stall point for
parallel builds.

Which of the above would you suggest,
or maybe you can think of something else?

[stsp]

I tried some work-arounds, but the
problem seems to be that meson
insists on the generator's input being
an actual existing file.
How can I disable such a check?
I'd like to pass arbitrary args to a
generator. Why meson prevents me
from doing that?

[stsp]

OK, I solved the problems by
tricking around the extra_args
property, together with writing
out some targets manually.