Clarify types/suffixes

[ghost]

Just to clarify -- there's are two mapping here. One is suffix -> type, used when we need to decide what's the type of the source file, and another is type->suffix, used to decide what's the suffix to use on generated targets. The first mapping, naturally, does not allow duplicate suffixes, but the second one does.

It's possible to first declare a type with no suffixes, and then use type.set-generated-target-suffix to specify generated suffix explicitly.

Will it help in your case?

Yup, we tested this and it does help in our case. We still need to

use the technique in the actual projects but I will get to that some time later today and I do not expect it to cause any problems.

Extender documentation does mention this rule but I would suggest

updating the docs to include both the explanation given in your previous post (about theer being two mappings and the type.register parameter being used to populate both of them) and possibly a paragraph such as:

'Types not used to model source but only generated files should

specify their file extension using the type.set-generated-target-suffix Boost.Build rule. This allows them to exist even if some other used Boost.Build module already defines a type with the same suffix name.'