Support disabling of implicit typing in package manifest

[awvwgk]

Motivation

Allow packages to opt-out from default implicit typing in Fortran. This allows to get the full befits of implicit none in every scope without having to remember typing it.

More difficult is whether we can find options in every compiler to actually guarantee that this is working.

Specification

The build table seems most appropriate for this option:

[build]
implicit-typing = false

Prior Art

Compiler flags:

compiler	option
GFortran	-fimplicit-none
NVHPC	-Mdclchk
nagfor	-u
Cray/HPE	-eI
SilverFrost FTN95	/IMPLICIT_NONE
ifort (Windows)	/warn:declarations,errors
ifort (Linux, macOS)	-warn declarations,errors
flang	-fimplicit-none-type-always
IBM XL Fortran	-qundef or -u

Additional Information

Related issue #359
Draft PR: #506

[epagone]

As mentioned in the linked PR, I'd like to give this a try, if you agree. If you do, any pointers are welcome.

[awvwgk]

Alright, here is a brief outline of a strategy to implement this feature. All references are based on the patch from #575.

To implement this feature we need to represent it in the package manifest, this happens in the derived types defined in src/fpm/manifest, every table has a corresponding source file there. For the implicit-typing I'd recommend to add another logical in the build table, you can follow one of the existing logical data types defined there.

fpm/src/fpm/manifest/build.f90

Lines 22 to 23 in beaf9a8

	!> Configuration data for build
	type :: build_config_t

The next step is to get the information into the fpm model, since this is a package resolved option, it shouldn't go into the top-level, but should be included in the package_t:

fpm/src/fpm_model.f90

Lines 96 to 105 in beaf9a8

	!> Type for describing a single package
	type package_t
	!> Name of package
	character(:), allocatable :: name
	!> Array of sources
	type(srcfile_t), allocatable :: sources(:)
	end type package_t

The package_t in the fpm model is build from the package manifest in src/fpm.f90:

fpm/src/fpm.f90

Lines 159 to 160 in beaf9a8

	model%packages(i)%name = dependency%name
	if (.not.allocated(model%packages(i)%sources)) allocate(model%packages(i)%sources(0))

Once you have the information about the implicit typing in the model, it must be made accessible in the target generation (src/fpm_targets.f90). The loop over the packages in the model is the right place to extract this information:

fpm/src/fpm_targets.f90

Line 195 in beaf9a8

do j=1,size(model%packages)

Eventually, the correct flag should be added to the compile_flags of the array of build_target_ptr. Adding it to the compile_flags for the Fortran targets automatically takes care everything (including the build hash), there is no need to adjust the build backend.

The remaining issue is to get the correct command line argument for enabling this option, the model has a compiler object which can be adjusted to provide the correct argument:

fpm/src/fpm_compiler.f90

Lines 72 to 81 in beaf9a8

	!> Definition of compiler object
	type :: compiler_t
	!> Identifier of the compiler
	integer(compiler_enum) :: id = id_unknown
	!> Path to the Fortran compiler
	character(len=:), allocatable :: fc
	!> Path to the C compiler
	character(len=:), allocatable :: cc
	!> Print all commands
	logical :: echo = .true.

[epagone]

Wow, thank you so much Sebastian @awvwgk !

[awvwgk]

You're welcome.

[ivan-pi]

I've updated the table of options with more compilers (see original issue post). Here are the sources for each of them:

• nagfor
• SilverFrost FTN95
• Cray/HPE
• flang
• XL Fortran (IBM)
• ifort

@certik, do you have a flag for LFortran already?

[certik]

It's the default in lfortran. I am in a process of adding a flag to enable implicit typing.

[awvwgk]

I guess this issue has gone stale for some time now.

@epagone I cleared your assignment to encourage others to pick it up.

[awvwgk]

I made a quick and hacky proof-of-concept implementation in 25f6553, which works with GFortran. Needs some more thoughts and polishing before this can become a pull request.