Question about binary distributions

[John Cotton Ericson]

Per https://gitlab.haskell.org/ghc/ghc/issues/17191 I do hope to break 
up our configure script soon.[1] Then the bindist will need not ship the 
"entire" configure script, but just what is necessary to fill in the 
settings file(s) which have that information Ben mentions.

I think that will improve the optics of the situation a bit; for 
example, I don't think the reduced bindist configure script should need 
to worry about directories at all since GHC is relocatable (when built 
by Hadrian).

John

[1]: I will be able to resume work on that once I get to the bottom of 
https://gitlab.haskell.org/ghc/ghc/merge_requests/1102. All help greatly 
appreciated!

On 8/7/20 11:15 AM, Ben Gamari wrote:
> "Mathieu Boespflug" <m at tweag.io> writes:
>
>> Hi all,
>>
>> GHC currently has 3 tier-1 platforms: Linux, macOS and Windows. I'll
>> focus the dicussion below on these three platforms. The binary
>> distributions for Linux and macOS are designed to be unpacked, then
>> the user types ./configure && make install. This is not the case for
>> Windows.
>>
>> On all platforms it's possible to create "relocatable" installations,
>> such that GHC doesn't really care where it's installed, and commands
>> will still work if the install directory changes location on the
>> filesystem. So my question is, why do we have a ./configure step on
>> Linux and macOS? Why could we not have bindists for all platforms that
>> work like the Windows one? I.e. a binary distribution that you just
>> unpack, in any directory of your choice, without any configuration or
>> installation step.
> There are a few reasons:
>
>   * Relocatable GHC builds have only been supported for only a few
>     releases now and only under the Hadrian build system, which is not
>     currently used to produce our binary distributions (hopefully this
>     will change for 9.2).
>
>   * On Windows we have the luxury of having a very well-controlled
>     environment as we rely on essentially nothing from the host
>     system. We provide our own mingw toolchain, statically link
>     against libc, and have no additional dynamic dependencies.
>
>     By contrast, on Linux we have to deal with a much larger
>     configuration space:
>
>      * several linkers, each with their own bugs
>
>      * several C compilers, supporting various subsets of functionality
>        and quirks (e.g. some distributions enable -pie by default, others
>        do not)
>
>      * various LLVM packaging schemes
>
>     Since it would be quite expensive to probe the toolchain
>     characteristics on every compiler invocation, we rather do this once
>     in the configure script during bindist installation and package the
>     result in the installed `settings` file.
>
>   * On Linux we may have additional dynamic dependencies (e.g. libdw,
>     numactl) which we check for during configuration time, lest the user
>     be faced with an unsightly linker error if they happen to be missing
>     a library.
>
> In principle we could perhaps avoid the need for many of these checks
> by creating one binary distribution per operating system distribution.
> However, we will first need to move to Hadrian to build our binary
> distributions.
>
> Cheers,
>
> - Ben
>
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