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Gentoo overlay for the D programming language
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README.md

dlang - overlay for Gentoo Linux

This overlay aims to make parallel installation of D compilers easy and offer some of the most popular D libraries. Features it offers:

  • Installation of DMD, GDC and LDC in parallel
  • Customizable »CFLAGS« for each D compiler
  • GDC is integrated with GCC for the best compatibility
  • Slotted installation of previous D compiler versions
  • Shared library support when using DMD
  • Easily compile debug builds with DMD and release builds with LDC/GDC even when they depend on libraries like GtkD. (Note: This depends on availability of libraries in this repository.)

Usage

The overlay supports linker and compiler flags, though some package build scripts may not be patched to use them (e.g. DMD). For D packages, the LDFLAGS variable is rewritten to match the D compilers linker prefix. For DMD this is -L and for LDC this is -L=. If you have not set up LDFLAGS in make.conf, the Gentoo default will be used, which is currently -Wl,--as-needed -Wl,-O1. Taking this example, in a compilation using DMD this would be rewritten to LDFLAGS=-L--as-needed -L-O1. Compiler flags are passed into build scripts as DCFLAGS, but since there is no common command-line syntax between D compilers they are split up into DMDFLAGS, GDCFLAGS and LDCFLAGS in make.conf. An example configuration could be:

DMDFLAGS="-O"
GDCFLAGS="-march=native -O3 -pipe -frelease"
LDCFLAGS="-O4 -release"

You may experiment with -ffunction-sections, -fdata-sections and the corresponding linker flag --gc-sections, but this caused broken exception handling in the past.

When you install libraries, no compilers will be selected to work with. Please run emerge -pv <lib> to list available compiler use flags for a library and use /etc/portage/package.use to activate them. A note about compilation times: Most build tools compile one module at a time, which causes a considerable overhead in compile times compared to passing multiple modules to the compiler at once. The use of several compilers in several versions and multilib installs all multiply the compile times. GtkD with no optional features compiled for one version of DMD, GDC and LDC took me 1 hour 10 minutes on a dual core 2 Ghz notebook.

Executables paths

  • DMD: /opt/dmd-<version>/bin/dmd
  • GDC: /usr/<abi>-pc-linux-gnu/gcc-bin/<version>/gdc
  • LDC: /opt/ldc2-<version>/bin/ldc2

An eselect script will create symlinks to these executables, so they can be called by their original names with the exception of GDC which is managed by gcc-config.

Configuration files

For DMD the configuration files lie side-by-side with the executable, to allow different path setups for each installation.

Imports

  • DMD: /opt/dmd-<version>/import
  • GDC: /usr/include/d/<version>
  • LDC: /opt/ldc2-<version>/include/d

Libraries

Dynamic and static libraries are installed into:

  • DMD: /opt/dmd-<version>/lib{32,64}
  • GDC: /usr/lib/gcc/<abi>-pc-linux-gnu/<version>[/32]
  • LDC: /opt/ldc2-<version>/lib{32,64}

Include files should be placed in /usr/include/dlang/<library>

Procedures

When adding new compiler versions

Add the version to dlang.eclass, too. This way it knows which compiler release builds on which version of the D language specification, which is crucial for dependency management.

When changing paths in compiler ebuilds

Make sure that dlang.eselect knows about it. dlang.eclass also has a function that needs to be changed: dlang_foreach_config() It advertizes compiler specific variables and paths to D ebuilds.

Q & A

Q: Why are D libraries not installed in their default locations? A: D compilers have ABIs that are incompatible with each other. This means either sticking to one compiler for anything D, or to change the default location and allow for one installation per compiler. Since my motivation was to use dmd for debug builds and one of the others for releases, I chose the second option. I could have just added prefixes or suffixes to the library names, but that means build scripts need to be aware of this change. Giving each compiler eco system its own library directory and seting up the path in the compiler should ideally allow us to build a D program with any compiler and link to libraries with no further configuration change.

Q: So why is there a library directory for each version of each D compiler? A: It might seem overkill at first, but we have no guarantee about D ABI stability at this point. Libraries compiled with 2.064 might not work with libraries compiled with 2.065. To be on the safe side, I decided to separate D specifications the same way as compilers.

TODO

  • Optional: For GtkD, make HTML DDOC generation work with any compiler and install them if the doc use flag is set.
  • Optional: Make dmd respect CFLAGS etc.
  • For GtkD, fix the pkg-config (.pc) script to point to the correct library dir or none (since it should be found in the default paths). Big question: What to do with the dmd specific "-L" prefixes?
  • What to do about rdmd and co.? Their man pages are in the 'dmd' repository, but the source code is in 'tools'.
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