module: add :lang fortran

* feat(fortran): account for f90 and fortran modes

* feat(fortran): initial keybindings

* feat(fortran): basic compilation

* feat(fortran): compilation popup

This customizes the name of the compilation buffer produced by the
`compile` function. We're keeping things simple; Emacs already knows how
to run compilation commands in a popup and parse the results, so let's
let it do its thing.

* feat(fortran): doctor checks

* docs(fortran): installation instructions

* feat(fortran): actual usage of fpm

* feat(fortran): configure compilation popups

* feat(fortran): improved raw gfortran usage

Although it's recommended to do everything through `fpm` to make life
easier.

* docs(fortran): backburner `+intel` for now

* feat(fortran): address PR suggestions

modules/lang/fortran/README.org

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+#+TITLE:   lang/fortran
+#+DATE:    October 22, 2021
+#+SINCE:   v3.0.0 (#5676)
+#+STARTUP: inlineimages nofold
+
+* Table of Contents :TOC_3:noexport:
+- [[#description][Description]]
+  - [[#maintainers][Maintainers]]
+  - [[#module-flags][Module Flags]]
+  - [[#plugins][Plugins]]
+- [[#prerequisites][Prerequisites]]
+  - [[#arch-linux][Arch Linux]]
+- [[#features][Features]]
+- [[#configuration][Configuration]]
+- [[#troubleshooting][Troubleshooting]]
+
+* Description
+
+This module enables a complete, modern development environment for the [[https://fortran-lang.org/][Fortran]]
+language. Initially released in 1956 (a year before Lisp 1.0), Fortran is the
+original high-performance computation language and is still widely used in
+science and academia. Popular versions of the language include Fortran 77 and
+Fortran 90, with further extensions in the 1995 and 2008 varieties. Today,
+Fortran has joined the modern age with its own [[https://github.com/fortran-lang/fpm][package manager]], [[https://fortran-lang.org/packages/][package
+registry]], and [[https://fortran-lang.discourse.group/][Discourse community]].
+
+In particular, this module features:
+
++ Support for all major Fortran varieties.
++ Auto-formatting via =fprettier=.
++ Integration with the =fpm= package manager.
++ LSP support via [[https://github.com/hansec/fortran-language-server][fortran-language-server]].
+
+#+begin_quote
+After a career of writing Fortran on Mainframes and Windows machines, my
+now-retired Dad is switching to Linux. Imagine my surprise when I learned that
+off-the-shelf setups for Fortran on Linux basically don't exist! Well, until
+now... Cheers Dad, hope this helps.
+#+end_quote
+
+** Maintainers
++ [[https://github.com/fosskers][@fosskers]] (Author)
+
+** Module Flags
++ =+lsp= Activate =fortran-language-server= for Fortran projects.
+
+** Plugins
+
+* Prerequisites
+
+For minimum functionality, this module requires =gfortran=. For most project
+management tasks you will also need [[https://github.com/fortran-lang/fpm][fpm]], the Fortran Package Manager.
+
+** Arch Linux
+
+=gfortran= is available from the official repositories:
+
+#+begin_example
+sudo pacman -S gcc-fortran
+#+end_example
+
+Whereas =fpm= is available from the AUR and thus must be installed with an
+AUR-compatible tool like [[https://github.com/fosskers/aura][Aura]]:
+
+#+begin_example
+sudo aura -A fortran-fpm
+#+end_example
+
+* Features
+# An in-depth list of features, how to use them, and their dependencies.
+
+* Configuration
+# How to configure this module, including common problems and how to address them.
+
+* Troubleshooting
+# Common issues and their solution, or places to look for help.

modules/lang/fortran/autoload.el

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+;;; lang/fortran/autoload.el -*- lexical-binding: t; -*-
+
+;; --- GFORTRAN --- ;;
+
+;;;###autoload
+(defun +fortran/gfortran-compile ()
+  "Compile the current buffer using gfortran."
+  (interactive)
+  (compile (format "gfortran %s %s"
+                   (+fortran/fortran-std)
+                   buffer-file-name)))
+
+;;;###autoload
+(defun +fortran/gfortran-run ()
+  "Run the current buffer using gfortran."
+  (interactive)
+  (delete-file "./a.out")
+  (+fortran/gfortran-compile)
+  (while (not (file-exists-p "./a.out"))
+    (sleep-for 1))
+  (compile "./a.out"))
+
+(defun +fortran/fortran-std ()
+  "Which version of Fortran should we target?"
+  (cl-case major-mode
+    (fortran-mode "-std=legacy")
+    (t "")))
+
+;; --- FPM --- ;;
+
+;;;###autoload
+(defun +fortran/fpm-build ()
+  "Build the current project using fpm."
+  (interactive)
+  (compile "fpm build"))
+
+;;;###autoload
+(defun +fortran/fpm-run ()
+  "Run the current project using fpm."
+  (interactive)
+  (compile "fpm run"))
+
+;;;###autoload
+(defun +fortran/fpm-test ()
+  "Test the current project using fpm."
+  (interactive)
+  (compile "fpm test"))
+
+;; --- MISC. --- ;;
+;;;###autoload
+(defun +fortran/compilation-buffer-name (mode)
+  "The name of the buffer produced by `compile'."
+  (interactive)
+  "*fortran-compilation*")

modules/lang/fortran/config.el

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+;;; lang/fortran/config.el -*- lexical-binding: t; -*-
+
+;;
+;;; Packages
+
+(use-package! f90
+  :defer t
+  :config
+  ;; --- Compilation --- ;;
+  ;; Used by `compile' (SPC c c)
+  (setq-hook! 'f90-mode-hook
+    compile-command "gfortran "
+    compilation-buffer-name-function #'+fortran/compilation-buffer-name)
+  (set-popup-rule! "^\\*fortran-compilation" :side 'right :size 0.5 :quit t)
+
+  ;; --- LSP Configuration --- ;;
+  (when (featurep! +lsp)
+    (setq lsp-clients-fortls-args '("--enable_code_actions" "--hover_signature"))
+    (add-hook 'f90-mode-local-vars-hook #'lsp!))
+
+  ;; --- Keybindings --- ;;
+  (map! :map f90-mode-map
+        :localleader
+        (:prefix ("f" . "fpm")
+         :desc "fpm build" "b" #'+fortran/fpm-build
+         :desc "fpm run"   "r" #'+fortran/fpm-run
+         :desc "fpm test"  "t" #'+fortran/fpm-test)
+        :desc "compile (gfortran)" "c" #'+fortran/gfortran-compile
+        :desc "run (gfortran)"     "r" #'+fortran/gfortran-run))
+
+(use-package! fortran
+  ;; The `.for' extension is automatically recognized by Emacs and invokes
+  ;; `fortran-mode', but not its capital variant `.FOR'. Many old files are
+  ;; named the latter way, so we account for that manually here.
+  :mode ("\\.FOR$" . fortran-mode)
+  :config
+  ;; Or else Flycheck will get very mad.
+  (setq flycheck-gfortran-language-standard "legacy")
+
+  ;; --- Compilation --- ;;
+  ;; Used by `compile' (SPC c c)
+  (setq-hook! 'fortran-mode-hook ; TODO These work for f90 but not for fortran.
+    compile-command "gfortran -std=legacy "
+    compilation-buffer-name-function #'+fortran/compilation-buffer-name)
+  (set-popup-rule! "^\\*fortran-compilation" :side 'right :size 0.5 :quit t)
+
+  ;; --- LSP --- ;;
+  ;; Strangely, the built-in flycheck support seems to give better hints than the LSP.
+  ;; (when (featurep! +lsp)
+  ;;   (setq lsp-clients-fortls-args '("--enable_code_actions" "--hover_signature"))
+  ;;   (add-hook 'fortran-mode-local-vars-hook #'lsp!)))
+
+  ;; --- Keybindings --- ;;
+  (map! :map fortran-mode-map
+        :localleader
+        :desc "compile (gfortran)" "c" #'+fortran/gfortran-compile
+        :desc "run (gfortran)"     "r" #'+fortran/gfortran-run))

modules/lang/fortran/doctor.el

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+;; -*- lexical-binding: t; no-byte-compile: t; -*-
+;;; lang/fortran/doctor.el
+
+(assert! (or (not (featurep! +lsp))
+             (featurep! :tools lsp))
+         "This module requires (:tools lsp)")
+
+(when (not (executable-find "gfortran"))
+  (warn! "Couldn't find gfortran - compilation will not work."))
+
+(unless (executable-find "fpm")
+  (warn! "Couldn't find fpm - project building/testing will not work."))
+
+(when (featurep! +lsp)
+  (unless (executable-find "fortls")
+    (warn! "Couldn't find fortls."))
+  (unless (executable-find "fprettify")
+    (warn! "Couldn't find fprettify.")))