Description

Fortran's default floating point precision is single precision, and the most used data type in scientific computing is floating point.

There are quite a few libraries (e.g. slsqp) that provide macro-based precision options, which seems very useful when developers don't want to write multiple precision versions of routines and polymorphic interfaces.

Is it possible to have macro definitions for dependency libraries in top-level projects, e.g.:

[features]
slsqp = ['REAL32']
minpack = ['REAL32']
M_stopwatch = ['_WIN32']

This also has a positive effect on the fpm library ecology.

Possible Solution

Style 1:

[dependencies]
slsqp.git = 'https://github.com/jacobwilliams/slsqp'
slsqp.tag = '1.4.1'
slsqp.features = ['REAL32']

Style 2:

[dependencies]
slsqp = { git = 'https://github.com/jacobwilliams/slsqp', tag = '1.4.1', features = ['REAL32'] }

Style 3:

[features]
slsqp = ['REAL32']

[dependencies]
slsqp.git = 'https://github.com/jacobwilliams/slsqp'
slsqp.tag = '1.4.1'

Additional Information

• cargo::features
• Fortran feature table #722