Add emacs-lisp formatting (#102)

* feat: add emacs-lisp formatting

* Disable indent-tabs-mode

* Add stub file for installation

* Fix lint errors

* fix: correctly format based on previous mode

* Formatting

* Fix weird indent

* Add checkindent target

* Update changelog

* Long line

* Empty commit

* fix ci

* revert changelog reformatting

* more changelog

* more

Co-authored-by: Radon Rosborough <radon.neon@gmail.com>
Co-authored-by: Radon Rosborough <radon@intuitiveexplanations.com>

9 files changed, 162 insertions, 78 deletions

diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index e06e4a7..eb79979 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -5,7 +5,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        emacs_version: [26, 27, "master"]
+        emacs_version: [26, 27, 28, "master"]
     steps:
       - name: Checkout
         uses: actions/checkout@v2
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 90b9f49..d87b17e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,9 +21,11 @@ The format is based on [Keep a Changelog].
 * [bean-format](https://github.com/beancount/beancount) for Beancount
   ([#101]).
 * [stylua](https://github.com/JohnnyMorganz/StyLua) for Lua ([#105]).
+* Native Emacs indentation of Emacs Lisp code as a formatter ([#102]).
 
 [#100]: https://github.com/radian-software/apheleia/pull/100
 [#101]: https://github.com/radian-software/apheleia/pull/101
+[#102]: https://github.com/radian-software/apheleia/pull/102
 [#105]: https://github.com/radian-software/apheleia/pull/105
 [#109]: https://github.com/radian-software/apheleia/issues/109
 [#110]: https://github.com/radian-software/apheleia/pull/110
diff --git a/Makefile b/Makefile
index 1f3ccd2..b5aea8f 100644
--- a/Makefile
+++ b/Makefile
@@ -1,3 +1,5 @@
+SHELL := bash
+
 VERSION ?=
 CMD ?=
 
@@ -8,6 +10,7 @@ TAG ?= latest
 # The order is important for compilation.
 for_compile := *.el
 for_checkdoc := *.el
+for_checkindent := *.el
 
 .PHONY: help
 help: ## Show this message
@@ -19,7 +22,7 @@ help: ## Show this message
 		column -t -s'|' >&2
 
 .PHONY: lint
-lint: compile checkdoc longlines fmt-lint ## Build project and run all linters
+lint: compile checkdoc longlines checkindent fmt-lint ## Run all fast linters
 
 .PHONY: compile
 compile: ## Check for byte-compiler errors
@@ -42,6 +45,24 @@ checkdoc: ## Check for missing or poorly formatted docstrings
 	        | grep . && exit 1 || true ;\
 	done
 
+.PHONY: checkindent
+checkindent: ## Ensure that indentation is correct
+	@tmpdir="$$(mktemp -d)"; for file in $(for_checkindent); do \
+	    echo "[checkindent] $$file" >&2; \
+	    emacs -Q --batch \
+		-l scripts/apheleia-indent.el \
+	        --eval "(setq inhibit-message t)" \
+	        --eval "(load (expand-file-name \"apheleia.el\") nil t)" \
+	        --eval "(find-file \"$$file\")" \
+	        --eval "(indent-region (point-min) (point-max))" \
+	        --eval "(write-file \"$$tmpdir/$$file\")"; \
+	    (diff <(cat          "$$file" | nl -v1 -ba | \
+                           sed "s/\t/: /" | sed "s/^ */$$file:/") \
+	          <(cat "$$tmpdir/$$file" | nl -v1 -ba | \
+                           sed "s/\t/: /" | sed "s/^ */$$file:/") ) \
+	        | grep -F ">" | grep -o "[a-z].*" | grep . && exit 1 || true; \
+	done
+
 .PHONY: longlines
 longlines: ## Check for long lines
 	@scripts/check-line-length.bash
diff --git a/apheleia.el b/apheleia.el
index a0acc54..df89471 100644
--- a/apheleia.el
+++ b/apheleia.el
@@ -363,20 +363,21 @@ NO-QUERY, and CONNECTION-TYPE."
          (stderr-file (apheleia--make-temp-file run-on-remote "apheleia"))
          (args
           (append
-           (list (car command)            ; argv[0]
-                 (not stdin)              ; If stdin we don't delete the STDIN
-                                          ; buffer text with
-                                          ; `call-process-region'. Otherwise we
-                                          ; send no INFILE argument to
-                                          ; `call-process'.
-                 `(,stdout ,stderr-file)  ; stdout buffer and stderr file.
-                                          ; `call-process' cannot capture
-                                          ; stderr into a separate buffer, the
-                                          ; best we can do is save and read
-                                          ; from a file.
-                 nil)                     ; Do not re/display stdout as output
-                                          ; is recieved.
-           (cdr command))))               ; argv[1:]
+           (list
+            ;; argv[0]
+            (car command)
+            ;; If stdin we don't delete the STDIN buffer text with
+            ;; `call-process-region'. Otherwise we send no INFILE
+            ;; argument to `call-process'.
+            (not stdin)
+            ;; stdout buffer and stderr file. `call-process' cannot
+            ;; capture stderr into a separate buffer, the best we can
+            ;; do is save and read from a file.
+            `(,stdout ,stderr-file)
+            ;; Do not re/display stdout as output is recieved.
+            nil)
+           ;; argv[1:]
+           (cdr command))))
     (unwind-protect
         (let ((exit-status
                (cl-letf* ((message (symbol-function #'message))
@@ -656,7 +657,9 @@ See `apheleia--run-formatters' for a description of REMOTE."
         (clear-files nil)
         (run-on-remote (and (eq apheleia-remote-algorithm 'remote)
                             remote)))
-    (cl-labels ((apheleia--make-temp-file-for-rcs-patch
+    (cl-labels ((;; Weird indentation because of differences in Emacs
+                 ;; indentation algorithm between 27 and 28
+                 apheleia--make-temp-file-for-rcs-patch
                  (buffer &optional fname)
                  ;; Ensure there's a file with the contents of `buffer' on the
                  ;; target machine. `fname', if given, refers to an existing
@@ -826,12 +829,12 @@ machine from the machine file is available on"))
                               arg
                             (eval arg)))
              if val
-               if (and (consp val)
-                       (cl-every #'stringp val))
-                 append val
-               else if (stringp val)
-                 collect val
-               else do (error "Result of command evaluation must be a string \
+             if (and (consp val)
+                     (cl-every #'stringp val))
+             append val
+             else if (stringp val)
+             collect val
+             else do (error "Result of command evaluation must be a string \
 or list of strings: %S" arg)))
       `(,input-fname ,output-fname ,stdin ,@command))))
 
@@ -928,6 +931,7 @@ being run, for diagnostic purposes."
     (gofmt . ("gofmt"))
     (google-java-format . ("google-java-format" "-"))
     (isort . ("isort" "-"))
+    (lisp-indent . apheleia-indent-lisp-buffer)
     (ktlint . ("ktlint" "--stdin" "-F"))
     (latexindent . ("latexindent" "--logfile=/dev/null"))
     (mix-format . ("mix" "format" "-"))
@@ -1000,6 +1004,26 @@ rather than using this system."
              (const :tag "Name of temporary file used for output" output)))
            (function :tag "Formatter function"))))
 
+(cl-defun apheleia-indent-lisp-buffer
+    (&key buffer scratch callback &allow-other-keys)
+  "Format a Lisp BUFFER.
+Use SCRATCH as a temporary buffer and CALLBACK to apply the
+transformation.
+
+For more implementation detail, see
+`apheleia--run-formatter-function'."
+  (with-current-buffer scratch
+    (setq-local indent-line-function
+                (buffer-local-value 'indent-line-function buffer))
+    (setq-local lisp-indent-function
+                (buffer-local-value 'lisp-indent-function buffer))
+    (funcall (with-current-buffer buffer major-mode))
+    (goto-char (point-min))
+    (let ((inhibit-message t)
+          (message-log-max nil))
+      (indent-region (point-min) (point-max)))
+    (funcall callback)))
+
 (defun apheleia--run-formatters
     (formatters buffer remote callback &optional stdin)
   "Run one or more code formatters on the current buffer.
@@ -1054,8 +1078,10 @@ function: %s" command)))
     (c-mode . clang-format)
     (c++-mode . clang-format)
     (caml-mode . ocamlformat)
+    (common-lisp-mode . lisp-indent)
     (css-mode . prettier)
     (dart-mode . dart-format)
+    (emacs-lisp-mode . lisp-indent)
     (elixir-mode . mix-format)
     (elm-mode . elm-format)
     (fish-mode . fish-indent)
@@ -1070,6 +1096,7 @@ function: %s" command)))
     (latex-mode . latexindent)
     (LaTeX-mode . latexindent)
     (lua-mode . stylua)
+    (lisp-mode . lisp-indent)
     (nix-mode . nixfmt)
     (python-mode . black)
     (ruby-mode . prettier)
diff --git a/scripts/apheleia-indent.el b/scripts/apheleia-indent.el
new file mode 100644
index 0000000..039cf51
--- /dev/null
+++ b/scripts/apheleia-indent.el
@@ -0,0 +1,6 @@
+;; This file has code that is evaluated in CI before the indentation
+;; of apheleia.el is checked. This is helpful because it allows us to
+;; ensure that various things are indented correctly if they require
+;; some setup for Emacs to know how to do the right thing.
+
+;; Nothing here yet though! ^_^
diff --git a/test/formatters/apheleia-ft.el b/test/formatters/apheleia-ft.el
index 26279ad..db2422b 100755
--- a/test/formatters/apheleia-ft.el
+++ b/test/formatters/apheleia-ft.el
@@ -218,65 +218,82 @@ environment variable, defaulting to all formatters."
             (out-file (replace-regexp-in-string
                        "/in\\([^/]+\\)" "/out\\1" in-file 'fixedcase))
             (exec-path
-                (append `(,(expand-file-name
-                            "scripts/formatters"
-                            (file-name-directory
-                             (file-truename
-                              ;; Borrowed with love from Magit
-                              (let ((load-suffixes '(".el")))
-                                (locate-library "apheleia"))))))
-                        exec-path)))
-        (mapc
-         (lambda (arg)
-           (when (memq arg '(file filepath input output inplace))
-             (cl-pushnew arg syms)))
-         command)
-        (when (or (memq 'file syms) (memq 'filepath syms))
-          (setq in-temp-real-file (apheleia-ft--write-temp-file
-                                   in-text extension)))
-        (when (or (memq 'input syms) (memq 'inplace syms))
-          (setq in-temp-file (apheleia-ft--write-temp-file
-                              in-text extension))
-          (when (memq 'inplace syms)
-            (setq out-temp-file in-temp-file)))
-        (when (memq 'output syms)
-          (setq out-temp-file (apheleia-ft--write-temp-file
-                               "" extension)))
-        (setq command
-              (mapcar
-               (lambda (arg)
-                 (pcase arg
-                   ((or `file `filepath)
-                    in-temp-real-file)
-                   ((or `input `inplace)
-                    in-temp-file)
-                   (`output
-                    out-temp-file)
-                   (_ arg)))
-               command))
-        (setq command (delq 'npx command))
+             (append `(,(expand-file-name
+                         "scripts/formatters"
+                         (file-name-directory
+                          (file-truename
+                           ;; Borrowed with love from Magit
+                           (let ((load-suffixes '(".el")))
+                             (locate-library "apheleia"))))))
+                     exec-path)))
         (setq stdout-buffer (get-buffer-create
                              (format "*apheleia-ft-stdout-%S" formatter)))
         (with-current-buffer stdout-buffer
           (erase-buffer))
-        (setq exit-status
-              (apply
-               #'call-process
-               (car command)
-               (unless (or (memq 'file syms)
-                           (memq 'input syms)
-                           (memq 'inplace syms))
-                 in-file)
-               (list stdout-buffer stderr-file)
-               nil
-               (cdr command)))
-        ;; Verify that formatter succeeded.
-        (unless (zerop exit-status)
-          (with-temp-buffer
-            (insert-file-contents stderr-file)
-            (princ (buffer-string)))
-          (error
-           "Formatter %s exited with status %S" formatter exit-status))
+        (if (functionp command)
+            (progn
+              (setq in-temp-file (apheleia-ft--write-temp-file
+                                  in-text extension))
+              (with-current-buffer (find-file-noselect in-temp-file)
+                (funcall command
+                         :buffer (current-buffer)
+                         :scratch (current-buffer)
+                         :formatter formatter
+                         :callback (lambda ()))
+                (copy-to-buffer stdout-buffer (point-min) (point-max))))
+          (progn
+
+            (with-current-buffer stdout-buffer
+              (erase-buffer))
+            (mapc
+             (lambda (arg)
+               (when (memq arg '(file filepath input output inplace))
+                 (cl-pushnew arg syms)))
+             command)
+            (when (or (memq 'file syms) (memq 'filepath syms))
+              (setq in-temp-real-file (apheleia-ft--write-temp-file
+                                       in-text extension)))
+            (when (or (memq 'input syms) (memq 'inplace syms))
+              (setq in-temp-file (apheleia-ft--write-temp-file
+                                  in-text extension))
+              (when (memq 'inplace syms)
+                (setq out-temp-file in-temp-file)))
+            (when (memq 'output syms)
+              (setq out-temp-file (apheleia-ft--write-temp-file
+                                   "" extension)))
+            (setq command
+                  (mapcar
+                   (lambda (arg)
+                     (pcase arg
+                       ((or `file `filepath)
+                        in-temp-real-file)
+                       ((or `input `inplace)
+                        in-temp-file)
+                       (`output
+                        out-temp-file)
+                       (_ arg)))
+                   command))
+            (setq command (delq 'npx command))
+            (setq stdout-buffer (get-buffer-create
+                                 (format "*apheleia-ft-stdout-%S" formatter)))
+            (setq exit-status
+                  (apply
+                   #'call-process
+                   (car command)
+                   (unless (or (memq 'file syms)
+                               (memq 'input syms)
+                               (memq 'inplace syms))
+                     in-file)
+                   (list stdout-buffer stderr-file)
+                   nil
+                   (cdr command)))
+            ;; Verify that formatter succeeded.
+            (unless (zerop exit-status)
+              (with-temp-buffer
+                (insert-file-contents stderr-file)
+                (princ (buffer-string)))
+              (error
+               "Formatter %s exited with status %S" formatter exit-status))))
         ;; Verify that formatter has not touched original file.
         (when in-temp-real-file
           (let ((in-text-now (apheleia-ft--read-file in-temp-real-file)))
diff --git a/test/formatters/installers/lisp-indent.bash b/test/formatters/installers/lisp-indent.bash
new file mode 100644
index 0000000..97dbfb0
--- /dev/null
+++ b/test/formatters/installers/lisp-indent.bash
@@ -0,0 +1 @@
+# Nothing to do here, this formatter is pure Emacs!
diff --git a/test/formatters/samplecode/lisp-indent/in.el b/test/formatters/samplecode/lisp-indent/in.el
new file mode 100644
index 0000000..3e9200d
--- /dev/null
+++ b/test/formatters/samplecode/lisp-indent/in.el
@@ -0,0 +1,5 @@
+;; -*- indent-tabs-mode: nil -*-
+(if (and (< 3 5)
+                (= 1 1))
+                                 (message "true")
+(message "false"))
diff --git a/test/formatters/samplecode/lisp-indent/out.el b/test/formatters/samplecode/lisp-indent/out.el
new file mode 100644
index 0000000..2b8c5a2
--- /dev/null
+++ b/test/formatters/samplecode/lisp-indent/out.el
@@ -0,0 +1,5 @@
+;; -*- indent-tabs-mode: nil -*-
+(if (and (< 3 5)
+         (= 1 1))
+    (message "true")
+  (message "false"))