Recommend Fortran compiler as a prerequisite

[f588ca1e-f96a-4dea-804d-c55eab873dab]

Recommend Fortran compiler as a prerequisite in the "installing from source" guide.

Depends on #26964

CC: @slel

Component: documentation

Keywords: gfortran

Author: Odile Bénassy, Samuel Lelièvre

Branch/Commit: u/slelievre/mrs/4/gfortran @ a35d77e

Reviewer: Michael Orlitzky

Issue created by migration from https://trac.sagemath.org/ticket/27054

[jdemeyer]

Description changed:

[jdemeyer]

comment:1

1. It's not completely correct to say that gfortran must be installed since Sage will install it if needed. It would be good to clarify that.

2. What's up with the changes to src/sage/combinat/tutorial.py? There should be a separate ticket for that.

[dimpase]

comment:3

Replying to @jdemeyer:

2. What's up with the changes to src/sage/combinat/tutorial.py? There should be a separate ticket for that.

there is one, in fact, by the same author. Using a wrong branch, I presume.

[fchapoton]

comment:4

NOTE: Authors should be filled with the author full name.

[embray]

comment:5

Retarging tickets optimistically to the next milestone. If you are responsible for this ticket (either its reporter or owner) and don't believe you are likely to complete this ticket before the next release (8.7) please retarget this ticket's milestone to sage-pending or sage-wishlist.

[dimpase]

comment:7

I don't like this from the point of Fortran point of view - it is possible to build Sage with e.g. Flang. Do not break this.

[slel]

Changed branch from u/galois/mrs/4/gfortran to u/slelievre/mrs/4/gfortran

[slel]

Changed keywords from none to gfortran

[slel]

Description changed:

--- 
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@@ -1,10 +1 @@
-Zerline ([@zerline](https://gitlab.com/zerline)) opened a merge request at https://gitlab.com/sagemath/sage/merge_requests/4:
-
----
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+Recommend Fortran compiler as a prerequisite in the "installing from source" guide.

[slel]

Changed author from Zerline to Odile Bénassy, Samuel Lelièvre

[slel]

Changed commit from c36d9b5 to a35d77e

[slel]

comment:9

Rephrased as a recommendation rather than a strict prerequisite.

---

New commits:

a35d77e

Recommend Fortran compiler in installation guide

[jhpalmieri]

comment:10

On OS X, for what it's worth, I have installed gfortran (6.4.0) and I routinely build Sage with the built-in version of clang plus this gfortran. So maybe in an ideal world, the version of gfortran should match the C compiler, but it doesn't seem to be strictly necessary. Or have I just been getting lucky?

[jhpalmieri]

comment:11

In more detail:

$ which gcc
/usr/bin/gcc
$ gcc --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 10.0.0 (clang-1000.11.45.5)
Target: x86_64-apple-darwin18.2.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
$ which gfortran
/usr/local/bin/gfortran
$ gfortran --version
GNU Fortran (GCC) 6.4.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[dimpase]

comment:12

Replying to @jhpalmieri:

On OS X, for what it's worth, I have installed gfortran (6.4.0) and I routinely build Sage with the built-in version of clang plus this gfortran. So maybe in an ideal world, the version of gfortran should match the C compiler, but it doesn't seem to be strictly necessary. Or have I just been getting lucky?

this is what we routinely do on OSX, so it does not look like a problem to me.

[jhpalmieri]

comment:13

My comment was in response to the proposed change, which includes the line "it is necessary to have matching versions of these two compilers".

[slel]

comment:14

Thanks for your feedback on my proposed phrasing in commit a35d77e:

A Fortran compiler (matching the C/C++ compiler) is recommended, although not a strict requirement: if none is present, gfortran will be built, and this might also trigger building gcc, since it is necessary to have matching versions of these two compilers. Thus having a Fortran compiler present and compatible with the C/C++ compiler (for example matching versions of gcc and gfortran, or Clang and Flang) can make the build simpler and faster.

How about the following?

A Fortran compiler is recommended, although not a strict requirement: if none is present, gfortran will be built, and this might also trigger building gcc, depending on the OS and on what C/C++ compiler and what version of it is present. Having a Fortran compiler compatible with the C/C++ compiler (for example matching versions of gcc and gfortran, or compatible versions of Clang and Flang, or of Clang and gfortran) can thus save time and power when building Sage.

[jhpalmieri]

comment:15

I'm happy with the revised version.

[embray]

comment:16

Ticket retargeted after milestone closed (if you don't believe this ticket is appropriate for the Sage 8.8 release please retarget manually)

[embray]

comment:17

Tickets still needing working or clarification should be moved to the next release milestone at the soonest (please feel free to revert if you think the ticket is close to being resolved).

[embray]

comment:18

Ticket retargeted after milestone closed

[mkoeppe]

comment:19

See also #26964, which generates the commands to install recommended system packages.

[mkoeppe]

Dependencies: #26964

[mkoeppe]

comment:21

26964 is ready and takes care of this.

[orlitzky]

Reviewer: Michael Orlitzky

[fchapoton]

comment:23

ok, thx