[nongnu] elpa/nix-mode ae2c44c160 250/500: Add nix-shell-haskell.el

[ELPA Syncer]

branch: elpa/nix-mode
commit ae2c44c160cf2e03dde6431212dd69cf436fec15
Author: Matthew Bauer <mjbauer95@gmail.com>
Commit: Matthew Bauer <mjbauer95@gmail.com>

    Add nix-shell-haskell.el
---
 Cask                 |   1 +
 nix-shell-haskell.el | 107 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 108 insertions(+)

diff --git a/Cask b/Cask
index 1e13441a88..0a1ae1d212 100644
--- a/Cask
+++ b/Cask
@@ -17,6 +17,7 @@
  "nix-search.el"
  "nix-shebang.el"
  "nix.el"
+ "nix-shell-haskell.el"
  )
 
 (development
diff --git a/nix-shell-haskell.el b/nix-shell-haskell.el
new file mode 100644
index 0000000000..01e56c21c0
--- /dev/null
+++ b/nix-shell-haskell.el
@@ -0,0 +1,107 @@
+;;; nix-shell-haskell.el -- run nix commands in Emacs -*- lexical-binding: t 
-*-
+
+;; Author: Matthew Bauer <mjbauer95@gmail.com>
+;; Homepage: https://github.com/NixOS/nix-mode
+;; Keywords: nix
+
+;; This file is NOT part of GNU Emacs.
+
+;;; Commentary:
+
+;; You can use nix-shell-haskell as a hook to haskell-mode.
+;; Just run:
+
+;; (require 'nix-shell-haskell)
+;; (add-hook 'haskell-mode 'nix-shell-haskell)
+
+;;; Code:
+
+(require 'nix)
+(require 'nix-instantiate)
+(require 'nix-shell)
+(require 'haskell)
+(require 'haskell-cabal)
+(require 'haskell-session)
+(require 'flycheck)
+
+(defun nix-shell-haskell--callback (buffer cabal-file drv &rest _)
+  "Run the nix-shell callback to setup the buffer.
+The BUFFER to run in.
+The CABAL-FILE to load from.
+The DRV file to use."
+  (let* ((env (alist-get 'env drv))
+        (stdenv (alist-get 'stdenv env))
+        (system (alist-get 'system env))
+        (inputs (remove nil
+                        (apply 'append
+                               (mapcar (lambda (prop)
+                                         (split-string (alist-get prop env)))
+                                       nix-shell-inputs)))))
+
+    ;; Prevent accidentally rebuilding the world.
+    (unless (file-directory-p stdenv)
+      (error
+       "Your stdenv at %s has not been built. Please run: nix-store -r %s"
+       stdenv stdenv))
+
+    ;; Make sure this .drv file can actually be built here.
+    (unless (string= system (nix-system))
+      (error
+       "Your system (%s) does not match .drv’s build system (%s)"
+       (nix-system) system))
+
+    (with-current-buffer buffer
+      (make-local-variable 'exec-path)
+
+      (dolist (input inputs)
+       (when (and (not (file-directory-p input))
+                  nix-shell-auto-realise)
+         (nix-store-realise input))
+
+       (add-to-list 'exec-path (expand-file-name "bin" input)))
+
+      (when flycheck-mode
+       (flycheck-buffer)))
+
+    (when (and (eq major-mode 'haskell-mode) (not (haskell-session-maybe)))
+      (message "here")
+      (unless (haskell-session-lookup cabal-file)
+       (let ((session (haskell-session-make cabal-file)))
+         (haskell-session-set-cabal-dir (file-name-directory cabal-file))
+         (haskell-process-start session)))
+      (haskell-session-assign cabal-file))))
+
+;;;###autoload
+(defun nix-shell-haskell (&optional cabal-file)
+  "Setup Nix shell from the .cabal file."
+  (interactive)
+  (unless cabal-file
+    (setq cabal-file (haskell-cabal-find-file)))
+  (when (and (called-interactively-p) (not cabal-file))
+    (error "Cannot find a cabal file in %s" default-directory))
+  (when cabal-file
+    (setq cabal-file (expand-file-name cabal-file))
+    (let ((file (concat (file-name-sans-extension cabal-file) ".nix"))
+         (project-dir (locate-dominating-file cabal-file "default.nix")))
+      (with-temp-file file
+       (insert "let\n")
+       (insert (format "  haskellPackages = %s.packages"
+                       (if project-dir (format "(import %s {})"
+                                               (expand-file-name
+                                                "default.nix" project-dir))
+                         "{}")))
+       (insert " or (import <nixpkgs> {}).haskellPackages;\n")
+       (insert "in\n")
+       (insert (format "  (haskellPackages.callCabal2nix \"%s\" \"%s\" {}).env"
+                       (file-name-base cabal-file) cabal-file))
+       (insert "  .overrideAttrs (attrs: {\n")
+       (insert "    nativeBuildInputs = (attrs.nativeBuildInputs or [])\n")
+       (insert "                        ++ (with haskellPackages; [ 
cabal-install ]);\n")
+       (insert "  })\n"))
+      (nix-instantiate-async (apply-partially 'nix-shell-haskell--callback
+                                             (current-buffer)
+                                             cabal-file)
+                            file))))
+
+(provide 'nix-shell-haskell)
+;;; nix-shell-haskell.el ends here