[nongnu] elpa/doc-show-inline 1c5837d2a6 01/12: Initial working version.

[ELPA Syncer]

branch: elpa/doc-show-inline
commit 1c5837d2a667d977a1bd90ba44ebd911cc660f26
Author: Campbell Barton <ideasman42@gmail.com>
Commit: Campbell Barton <ideasman42@gmail.com>

    Initial working version.
---
 .elisp-autofmt     |   0
 LICENSE            | 674 ++++++++++++++++++++++++++++++++++++++
 doc-show-inline.el | 926 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 readme.rst         | 148 +++++++++
 4 files changed, 1748 insertions(+)

diff --git a/.elisp-autofmt b/.elisp-autofmt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000000..f288702d2f
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,674 @@
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+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/doc-show-inline.el b/doc-show-inline.el
new file mode 100644
index 0000000000..4bf8597124
--- /dev/null
+++ b/doc-show-inline.el
@@ -0,0 +1,926 @@
+;;; doc-show-inline.el --- Show doc-strings found in external files -*- 
lexical-binding: t -*-
+
+;; Copyright (C) 2021  Campbell Barton
+
+;; Author: Campbell Barton <ideasman42@gmail.com>
+
+;; URL: https://gitlab.com/ideasman42/emacs-doc-show-inline
+;; Keywords: convenience
+;; Version: 0.1
+;; Package-Requires: ((emacs "26.2"))
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This package overlays doc-strings (typically from C/C++ headers).
+;;
+
+;;; Usage
+
+;;
+;; Write the following code to your .emacs file:
+;;
+;;   (require 'doc-show-inline)
+;;
+;; Or with `use-package':
+;;
+;;   (use-package doc-show-inline)
+;;
+;; If you prefer to enable this per-mode, you may do so using
+;; mode hooks instead of calling `doc-show-inline-mode'.
+;; The following example enables this for C-mode:
+;;
+;;   (add-hook 'c-mode-hook
+;;     (lambda ()
+;;       (doc-show-inline-mode)))
+;;
+
+;;; Code:
+
+;; Built-in packages.
+(require 'xref)
+(require 'imenu)
+
+
+;; ---------------------------------------------------------------------------
+;; Custom Variables
+
+(defgroup doc-show-inline nil
+  "Overlay doc-strings from external files (using `xref' look-up)."
+  :group 'convenience)
+
+(defcustom doc-show-inline-idle-delay-init 1.0
+  "Initial idle delay, `doc-show-inline-idle-delay' is used afterwards."
+  :type 'float)
+
+(defcustom doc-show-inline-idle-delay 0.75
+  "Idle time to wait before highlighting.
+Set to 0.0 to highlight immediately (as part of syntax highlighting)."
+  :type 'float)
+
+(defcustom doc-show-inline-face-background-highlight -0.04
+  "Use to tint the background color for overlay text (between -1.0 and 1.0).
+Ignored when `doc-show-inline-face'
+does not have a user defined background color."
+  :type 'float)
+
+(defface doc-show-inline-face
+  (list (list t :extend t))
+  "Background for overlays.
+Note that the `background' is initialized using
+`doc-show-inline-face-background-highlight' unless it's customized.")
+
+;; TODO, document and make public.
+(defvar doc-show-inline-mode-defaults
+  (list
+    (cons 'c-mode (list :filter 'doc-show-inline-filter-for-cc-mode))
+    (cons 'cc-mode (list :filter 'doc-show-inline-filter-for-cc-mode))
+    (cons 'objc-mode (list :filter 'doc-show-inline-filter-for-cc-mode)))
+  "An association-list of default functions.")
+
+(defcustom doc-show-inline-use-logging nil
+  "Optionally log interactions.
+Use for troubleshooting when lookups aren't or debugging.
+Note that this should not be enabled general usage as it impacts performance."
+  :type 'boolean)
+
+
+;; ---------------------------------------------------------------------------
+;; Custom Functions
+
+(defvar doc-show-inline-fontify-hook nil
+  "Run before extraction, functions take two arguments for the comment range.
+Intended for any additional highlighting such as tags or spell checking text,
+note that highlighting from overlays are also supported.")
+
+(defvar doc-show-inline-buffer-hook nil
+  "Run upon loading a new buffer.
+This hook is called instead of the mode hooks such as:
+`c-mode-hook' and `after-change-major-mode-hook'.")
+
+(defvar-local doc-show-inline-locations 'doc-show-inline-locations-default
+  "Scans the current buffer for locations that `xref' should look-up.")
+
+(defvar-local doc-show-inline-extract-doc 'doc-show-inline-extract-doc-default
+  "Function to extract the doc-string given the destination buffer.
+The buffer and point will be the destination (the header file for example).
+The function must return a (BEG . END) cons cell representing the range
+or nil on failure.")
+
+(defvar-local doc-show-inline-filter nil
+  "Optionally skip some symbols when this function returns nil.
+The function takes a string (the symbol being looked up).
+When unset, the :filter property from `doc-show-inline-mode-defaults' is 
used.")
+
+
+;; ---------------------------------------------------------------------------
+;; Internal Variables
+
+(defconst doc-show-inline--cc-modes '(c-mode c++-mode objc-mode))
+
+;; Allow disabling the mode (when opening buffers for the purpose of 
introspection).
+(defvar doc-show-inline--inhibit-mode nil)
+
+;; Allow disabling for debugging.
+(defconst doc-show-inline--use-lookup-cache t)
+;; Always set when the mode is active:
+;; - key: the symbol as a string (from `xref-backend-identifier-at-point'),
+;; - value: the syntax-highlighted string to display (from 
`doc-show-inline--doc-from-xref').
+(defvar-local doc-show-inline--lookup-cache nil)
+
+(defvar-local doc-show-inline--idle-timer nil)
+
+
+;; ---------------------------------------------------------------------------
+;; Idle Overlay (Package Development / Debugging Only)
+;;
+;; Not intended for general purpose use,
+;; needed for checking there are no gaps in the regions being checked .
+
+;; Only for showing areas marked for highlighting.
+(defconst doc-show-inline--idle-overlays-debug nil)
+;; When debug is enabled.
+(defvar doc-show-inline--idle-overlays-debug-index 0)
+(defvar doc-show-inline--idle-overlays-debug-colors
+  (list "#005500" "#550000" "#000055" "#550055" "#005555"))
+
+
+;; ---------------------------------------------------------------------------
+;; Internal Functions / Macros
+
+(defmacro doc-show-inline--with-advice (fn-orig where fn-advice &rest body)
+  "Execute BODY with WHERE advice on FN-ORIG temporarily enabled."
+  `
+  (let ((fn-advice-var ,fn-advice))
+    (unwind-protect
+      (progn
+        (advice-add ,fn-orig ,where fn-advice-var)
+        ,@body)
+      (advice-remove ,fn-orig fn-advice-var))))
+
+(defun doc-show-inline--color-highlight (color factor)
+  "Tint between COLOR by FACTOR in (-1..1).
+Where positive brighten and negative numbers darken."
+  (let
+    (
+      (value (color-values color))
+      (factor-int (truncate (* 65535 factor))))
+    (apply 'format
+      (cons
+        "#%02x%02x%02x"
+        (mapcar
+          #'
+          (lambda (n)
+            ;; Shift by -8 to map the value returned by `color values':
+            ;; 0..65535 to 0..255 for `#RRGGBB` string formatting.
+            (ash (min 65535 (max 0 (truncate (+ (nth n value) factor-int)))) 
-8))
+          (number-sequence 0 2))))))
+
+(defun doc-show-inline--buffer-substring-with-overlay-props (pos-beg pos-end)
+  "Return text between POS-BEG and POS-END including overlay properties."
+  (let
+    ( ;; Extract text and possible overlays.
+      (text (buffer-substring pos-beg pos-end))
+      (text-length (- pos-end pos-beg))
+      (overlays (overlays-in pos-beg pos-end)))
+    (while overlays
+      (let ((ov (pop overlays)))
+        (let ((face-prop (overlay-get ov 'face)))
+          (when face-prop
+            (add-face-text-property
+              (max (- (overlay-start ov) pos-beg) 0)
+              (min (- (overlay-end ov) pos-beg) text-length)
+              face-prop
+              t
+              text)))))
+    text))
+
+
+;; ---------------------------------------------------------------------------
+;; Logging
+;;
+;; Without detailed logging, it's difficult to know why a doc-string is not 
found,
+;; this is quite verbose and intended for troubleshooting only.
+
+(defun doc-show-inline--log-type-impl (prefix str)
+  "Logging function (implementation), PREFIX and STR (with no newline)."
+  (let ((buf (get-buffer-create "*doc-show-inline-log*")))
+    (set-text-properties 0 (length str) nil str)
+    ;; (printf "%s%s\n" prefix str)
+    (with-current-buffer buf (insert prefix str "\n"))))
+
+(defmacro doc-show-inline--log-fail (&rest args)
+  "Log failure messages formatted with ARGS."
+  `
+  (when doc-show-inline-use-logging
+    (doc-show-inline--log-type-impl "Fail: " (format ,@args))))
+
+(defmacro doc-show-inline--log-info (&rest args)
+  "Log info messages formatted with ARGS."
+  `
+  (when doc-show-inline-use-logging
+    (doc-show-inline--log-type-impl "Info: " (format ,@args))))
+
+
+;; ---------------------------------------------------------------------------
+;; Mode Specific Logic
+;;
+;; Currently only C/C++ has custom support, other languages will work in 
principle
+;; if their doc-strings are stored externally and support `xref'.
+
+(defun doc-show-inline-filter-for-cc-mode (sym)
+  "Return non-nil when this SYM should be checked for a doc-string.
+
+The point will be located over the symbol (typically at it's beginning),
+the point should not be moved by this function."
+  (let ((prefix (buffer-substring-no-properties (line-beginning-position) 
(point))))
+    (cond
+      ;; Ignore defines, they never have external docs.
+      ;; Removing will work, it just performs an unnecessary lookup.
+      ((string-match-p "[ \t]*#[ \t]*define[ \t]+" prefix)
+        nil)
+      ;; Ignore static function doc-strings.
+      ;; Removing will work, it just performs an unnecessary lookup.
+      ((string-match-p "\\_<static\\_>" prefix)
+        nil)
+      ;; Forward declaring structs shouldn't show documentation, e.g:
+      ;;    struct SomeStruct;
+      ;; while this is in some sense a personal preference,
+      ;; forward declarations are mostly used to prevent warnings when these
+      ;; structs are used as parameters.
+      ;; So it makes sense to ignore them.
+      ( ;; Match: struct sym;
+        (and
+          (string-match-p "^\\_<struct\\_>" prefix)
+          (equal ?\; (char-after (+ (point) (length sym)))))
+        nil)
+      ;; Including `typedef' rarely gains anything from in-lining doc-string
+      ;; Similar to `struct':
+      ;; - This is already the declaration so the doc-string is already 
available.
+      ;; - This forward declares an opaque type.
+      ((string-match-p "^\\_<typedef\\_>" prefix)
+        nil)
+      (t
+        t))))
+
+(defun doc-show-inline-extract-doc-default (sym)
+  "Extract doc-string for SYM."
+  (let
+    (
+      ;; There may be blank lines between the comment beginning.
+      (pos-end
+        (progn
+          (beginning-of-line)
+          (skip-chars-backward " \t\n" (point-min))
+          (point))))
+
+    ;; Move one character into the comment.
+    (cond
+      ((forward-comment -1)
+        (let
+          (
+            (pos-beg (point))
+            (pos-beg-of-line (line-beginning-position)))
+
+          (cond
+            (
+              ;; Ensure the comment is not a trailing comment of a previous 
line.
+              (not
+                (eq
+                  pos-beg-of-line
+                  (save-excursion
+                    (skip-chars-backward " \t" pos-beg-of-line)
+                    (point))))
+              (doc-show-inline--log-info
+                "symbol \"%s\" in %S at point %d is previous lines trailing 
comment"
+                sym
+                (current-buffer)
+                (point))
+              ;; Failure.
+              nil)
+
+            (t
+              ;; Success.
+              (cons pos-beg pos-end)))))
+      (t
+        (doc-show-inline--log-info
+          "symbol \"%s\" in %S at point %d has no comment before it"
+          sym
+          (current-buffer)
+          (point))
+        ;; Failure.
+        nil))))
+
+
+;; ---------------------------------------------------------------------------
+;; Internal Functions / Macros
+
+(defun doc-show-inline--init-face-background-once ()
+  "Ensure `doc-show-inline-face' has a background color."
+  (when (eq 'unspecified (face-attribute 'doc-show-inline-face :background))
+    (let*
+      ( ;; Tint the color.
+        (default-color (face-attribute 'default :background))
+        (default-tint
+          (doc-show-inline--color-highlight
+            default-color
+            doc-show-inline-face-background-highlight)))
+      ;; Ensure there is some change, otherwise tint in the opposite direction.
+      (when (equal default-color default-tint)
+        (setq default-tint
+          (doc-show-inline--color-highlight
+            default-color
+            (- doc-show-inline-face-background-highlight))))
+      (set-face-attribute 'doc-show-inline-face nil :background 
default-tint))))
+
+(defun doc-show-inline--overlays-remove (&optional pos-beg pos-end)
+  "Remove overlays between POS-BEG & POS-END."
+  (cond
+    ;; When logging remove overlays one at a time.
+    (doc-show-inline-use-logging
+      (let ((overlays-in-view (overlays-in (or pos-beg (point-min)) (or 
pos-end (point-max)))))
+        (when overlays-in-view
+          (while overlays-in-view
+            (let ((ov (pop overlays-in-view)))
+              (when (and (overlay-get ov 'doc-show-inline) (overlay-buffer ov))
+                (doc-show-inline--log-info
+                  "removing overlay in %S at point %d" (current-buffer)
+                  ;; Start & end are the same.
+                  (overlay-start ov))
+                (delete-overlay ov)))))))
+    (t
+      (remove-overlays pos-beg pos-end 'doc-show-inline t))))
+
+(defun doc-show-inline--pos-in-overlays (pos overlays)
+  "Return non-nil when POS is within OVERLAYS."
+  (let ((result nil))
+    (while overlays
+      (let ((ov (pop overlays)))
+        (when (and (>= pos (overlay-start ov)) (< pos (overlay-end ov)))
+          (setq result t)
+          ;; Break.
+          (setq overlays nil))))
+    result))
+
+;; See https://emacs.stackexchange.com/questions/30673
+;; (adapted from `which-function').
+(defun doc-show-inline-locations-default (pos-beg pos-end)
+  "Return `imenu' positions for the current buffer between POS-BEG and 
POS-END."
+  ;; Ensure `imenu--index-alist' is populated.
+  (unless imenu--index-alist
+    (condition-case-unless-debug err
+      ;; Note that in some cases a file will fail to parse,
+      ;; typically when the file is intended for another platform (for 
example).
+      (imenu--make-index-alist)
+      (error
+        (doc-show-inline--log-fail "IMENU couldn't access symbols (failed to 
parse?): %s" err))))
+  (let
+    (
+      (alist imenu--index-alist)
+      (pair nil)
+      (mark nil)
+      (imstack nil)
+      (result nil))
+    ;; Elements of alist are either ("name" . marker), or
+    ;; ("submenu" ("name" . marker) ... ). The list can be
+    ;; Arbitrarily nested.
+    (while (or alist imstack)
+      (cond
+        (alist
+          (setq pair (car-safe alist))
+          (setq alist (cdr-safe alist))
+          (cond
+            ((atom pair)) ;; Skip anything not a cons.
+
+            ((imenu--subalist-p pair)
+              (setq imstack (cons alist imstack))
+              (setq alist (cdr pair)))
+
+            ((number-or-marker-p (setq mark (cdr pair)))
+              (let ((pos (marker-position mark)))
+                (unless (or (and pos-beg (<= pos pos-beg)) (and pos-end (>= 
pos pos-end)))
+                  (push pos result))))))
+        (t
+          (setq alist (car imstack))
+          (setq imstack (cdr imstack)))))
+
+    result))
+
+(defun doc-show-inline--xref-list-from-definitions (sym xref-backend)
+  "Return a list of XREF items from the identifier SYM at the current point.
+
+Argument XREF-BACKEND is used to avoid multiple calls to `xref-find-backend'."
+  (let ((xref-list nil))
+    (doc-show-inline--with-advice 'xref--not-found-error
+      :override (lambda (_kind _input) nil)
+      (doc-show-inline--with-advice 'xref--show-defs
+        :override
+        (lambda (fetcher _display-action) (setq xref-list (funcall fetcher)))
+        (let ((xref-prompt-for-identifier nil))
+          ;; Needed to suppress `etags' from requesting a file.
+          (doc-show-inline--with-advice 'read-file-name
+            :override
+            (lambda (&rest _args)
+              (doc-show-inline--log-info
+                "XREF lookup %S requested a file name for backend %S"
+                (current-buffer)
+                xref-backend)
+              ;; File that doesn't exist.
+              (user-error "Doc-show-inline: ignoring request for file read"))
+            (with-demoted-errors "%S" (xref-find-definitions sym))))))
+    xref-list))
+
+(defun doc-show-inline--doc-from-xref (sym xref-list)
+  "XREF-LIST is a list of `xref' items for SYM."
+  ;; Build a list of comments from the `xref' list (which may find multiple 
sources).
+  ;; In most cases only a single item is found.
+  ;; Nevertheless, best combine all so a doc-string will be extracted from at 
least one.
+  (let
+    (
+      (text-results nil)
+      (current-buf (current-buffer)))
+
+    ;; Don't enable additional features when loading files
+    ;; only for the purpose of reading their comments.
+    ;; `doc-show-inline-fontify-hook' can be used to enable features needed 
for comment extraction.
+    (save-excursion
+      (doc-show-inline--with-advice 'run-mode-hooks
+        :override
+        (lambda (_hooks) (run-hooks 'doc-show-inline-buffer-hook))
+
+        (dolist (item xref-list)
+          (let*
+            ( ;; This sets '(point)' which is OK in this case.
+              (marker (xref-location-marker (xref-item-location item)))
+              (buf (marker-buffer marker)))
+            ;; Ignore matches in the same buffer.
+            ;; While it's possible doc-strings could be at another location 
within this buffer,
+            ;; in practice, this is almost never done.
+            (unless (eq buf current-buf)
+
+              (with-current-buffer buf
+                (goto-char marker)
+                (pcase-let ((`(,pos-beg . ,pos-end) (funcall 
doc-show-inline-extract-doc sym)))
+                  (when (and pos-beg pos-end)
+                    ;; Ensure the comment is properly syntax highlighted,
+                    ;; note that we could assume this only uses the comment 
face
+                    ;; however some configurations highlight tags such as TODO
+                    ;; or even bad spelling, so font lock this text.
+                    (font-lock-ensure pos-beg pos-end)
+
+                    (run-hook-with-args 'doc-show-inline-fontify-hook pos-beg 
pos-end)
+
+                    (let
+                      (
+                        (text
+                          
(doc-show-inline--buffer-substring-with-overlay-props pos-beg pos-end)))
+                      (push text text-results))))))))))
+
+    (cond
+      (text-results ;; Add a blank item so there is a trailing newline when 
joining.
+        (let ((text (string-join (reverse (cons "" text-results)) "\n")))
+          (add-face-text-property 0 (length text) 'doc-show-inline-face t text)
+          text))
+      (t
+        nil))))
+
+(defun doc-show-inline--show-text (pos text)
+  "Add an overlay from TEXT at POS."
+  (doc-show-inline--log-info
+    "adding overlay in %S at point %d has %d length text"
+    (current-buffer)
+    pos
+    (length (or text "")))
+
+  (let ((ov (make-overlay pos pos)))
+    ;; Handy for debugging pending regions to be checked.
+
+    (overlay-put ov 'before-string text)
+    (overlay-put ov 'doc-show-inline t)
+    ov))
+
+(defun doc-show-inline--idle-overlays (pos-beg pos-end)
+  "Return a list of valid overlays between POS-BEG and POS-END."
+  (let ((result nil))
+    (let ((overlays-in-view (overlays-in pos-beg pos-end)))
+      (when overlays-in-view
+        (while overlays-in-view
+          (let ((ov (pop overlays-in-view)))
+            (when (and (overlay-get ov 'doc-show-inline-pending) 
(overlay-buffer ov))
+              (push ov result))))))
+    result))
+
+(defun doc-show-inline--idle-overlays-remove (&optional pos-beg pos-end)
+  "Remove `doc-show-inline-pending' overlays from current buffer.
+If optional arguments POS-BEG and POS-END exist
+remove overlays from range POS-BEG to POS-END.
+Otherwise remove all overlays."
+  (remove-overlays pos-beg pos-end 'doc-show-inline-pending t))
+
+(defun doc-show-inline--idle-handle-pos (pos sym xref-backend)
+  "Add text for the overlay at POS for SYM.
+XREF-BACKEND is the back-end used to find this symbol."
+  (cond
+    ;; Check if the symbol should be considered for doc-strings,
+    ;; some symbols might not make sense such as: '#define FOO' in C
+    ;; which can't have been declared elsewhere.
+    ((null (funcall doc-show-inline-filter sym))
+      (doc-show-inline--log-info
+        "symbol \"%s\" in %S at point %d has been ignored by filter %S"
+        sym
+        (current-buffer)
+        pos
+        doc-show-inline-filter))
+    (t ;; Symbol is valid and not filtered out.
+
+      (let ((text t))
+        (when doc-show-inline--use-lookup-cache
+          (setq text (gethash sym doc-show-inline--lookup-cache t)))
+
+        ;; When true, the value doesn't exist in cache.
+        (cond
+          ((eq text t)
+            (setq text nil)
+            (let ((xref-list (doc-show-inline--xref-list-from-definitions sym 
xref-backend)))
+              (doc-show-inline--log-info
+                "symbol \"%s\" in %S at point %d has %d reference(s)"
+                sym
+                (current-buffer)
+                pos
+                (length xref-list))
+              ;; Loads a buffer.
+              (when xref-list
+                (setq text (doc-show-inline--doc-from-xref sym xref-list))))
+
+            ;; Cache, even when nil (to avoid future lookups to establish it's 
nil).
+            (when doc-show-inline--use-lookup-cache
+              (puthash sym text doc-show-inline--lookup-cache))
+
+            (doc-show-inline--log-info
+              "symbol \"%s\" in %S at point %d has %d length text"
+              sym
+              (current-buffer)
+              pos
+              (length (or text ""))))
+          ;; Otherwise cache is used, text is either nil or a string.
+          (t
+            (doc-show-inline--log-info
+              "symbol \"%s\" in %S at point %d has %d length text (cached)"
+              sym
+              (current-buffer)
+              pos
+              (length (or text "")))))
+
+        (when text
+          (doc-show-inline--show-text (line-beginning-position) text))))))
+
+(defun doc-show-inline--idle-handle-pending-ranges ()
+  "Handle all queued ranges."
+  ;; First remove any overlays.
+  (when-let ((overlays-in-view (doc-show-inline--idle-overlays (point-min) 
(point-max))))
+    (let
+      (
+        (overlays-beg (point-max))
+        (overlays-end (point-min)))
+
+      (dolist (ov overlays-in-view)
+        (let
+          (
+            (ov-beg (overlay-start ov))
+            (ov-end (overlay-end ov)))
+          (doc-show-inline--overlays-remove ov-beg ov-end)
+
+          ;; Calculate the range while removing overlays.
+          (setq overlays-beg (min overlays-beg ov-beg))
+          (setq overlays-end (max overlays-end ov-end))))
+
+      (save-excursion
+        ;; There is something to do, postpone accessing `points'.
+        (let ((points (funcall doc-show-inline-locations (point-min) 
(point-max))))
+          (doc-show-inline--log-info
+            "found %d identifier(s) in %S"
+            (length points)
+            (current-buffer))
+          (when points
+            (let
+              ( ;; When loading buffers for introspection,
+                ;; there is no need to add `doc-show-inline' there (harmless 
but not necessary).
+                (doc-show-inline--inhibit-mode t)
+
+                (temporary-buffers (list))
+
+                (xref-backend (xref-find-backend)))
+
+              ;; Track buffers loaded.
+              (doc-show-inline--with-advice 'create-file-buffer
+                :around
+                (lambda (fn-orig filename)
+                  (let ((buf (funcall fn-orig filename)))
+                    (when buf
+                      (push buf temporary-buffers))
+                    buf))
+
+                (while points
+                  (let ((pos (pop points)))
+                    (cond
+                      ((null (doc-show-inline--pos-in-overlays pos 
overlays-in-view))
+                        (doc-show-inline--log-info
+                          "symbol \"%s\" in %S at point %d is not in the 
overlay list"
+                          (save-excursion
+                            (goto-char pos)
+                            (xref-backend-identifier-at-point xref-backend))
+                          (current-buffer)
+                          pos))
+                      (t
+                        (goto-char pos)
+                        (let ((sym (xref-backend-identifier-at-point 
xref-backend)))
+                          (cond
+                            ((null sym)
+                              (doc-show-inline--log-fail
+                                "can't find symbol in %S at point %d using 
`xref-backend' %S"
+                                (current-buffer)
+                                pos
+                                xref-backend))
+                            (t
+                              (doc-show-inline--idle-handle-pos pos sym 
xref-backend)))))))))
+
+              ;; Close any buffers loaded only for the purpose of extracting 
text.
+              (mapc 'kill-buffer temporary-buffers)))))
+
+      ;; Do this last, in the unlikely event of an error or an interruption,
+      ;; these overlays will be used again to ensure everything is updated.
+      (doc-show-inline--idle-overlays-remove overlays-beg overlays-end))))
+
+(defun doc-show-inline--idle-font-lock-region-pending (pos-beg pos-end)
+  "Track the range to check for overlays, adding POS-BEG & POS-END to the 
queue."
+  (let ((ov (make-overlay pos-beg pos-end)))
+    (doc-show-inline--log-info "idle overlay [%d..%d] in %S" pos-beg pos-end 
(current-buffer))
+
+    ;; Handy for debugging pending regions to be checked.
+    ;; (overlay-put ov 'face '(:background "#000000" :extend t))
+
+    (overlay-put ov 'doc-show-inline-pending t)
+
+    (overlay-put ov 'evaporate 't)
+
+    (doc-show-inline--timer-ensure t))
+
+  ;; Debug only, disabled by default.
+  (when doc-show-inline--idle-overlays-debug
+    (setq doc-show-inline--idle-overlays-debug-index
+      (1+ doc-show-inline--idle-overlays-debug-index))
+    (when
+      (>=
+        doc-show-inline--idle-overlays-debug-index
+        (length doc-show-inline--idle-overlays-debug-colors))
+      (setq doc-show-inline--idle-overlays-debug-index 0))
+    (let ((ov (make-overlay pos-beg pos-end)))
+      (overlay-put ov 'doc-show-inline-idle-overlay-debug t)
+      (overlay-put
+        ov 'face
+        (list
+          :background
+          (nth
+            doc-show-inline--idle-overlays-debug-index
+            doc-show-inline--idle-overlays-debug-colors)
+          :extend t)))))
+
+(defun doc-show-inline--timer-callback-or-disable (this-timer buf)
+  "Callback run from the idle timer THIS-TIMER for BUF."
+  ;; Ensure all other buffers are highlighted on request.
+  (cond
+    ((null (buffer-name buf))
+      (doc-show-inline--log-info "idle timer ignored for invalid buffer %S" 
buf)
+      ;; The buffer has been deleted, so cancel the timer directly.
+      (cancel-timer this-timer))
+    (t
+      (with-current-buffer buf
+        (cond
+          ((null (get-buffer-window buf t))
+            (doc-show-inline--log-info "idle timer ignored for buffer %S 
without a window" buf))
+          ((null (bound-and-true-p doc-show-inline-mode))
+            (doc-show-inline--log-info
+              "idle timer ignored for buffer %S without `doc-show-inline-mode' 
set"
+              buf))
+          (t
+            (doc-show-inline--log-info "idle timer for buffer %S callback 
running..." buf)
+            ;; In the unlikely event of an error, run the timer again.
+            (doc-show-inline--idle-handle-pending-ranges)))
+
+        (doc-show-inline--timer-ensure nil)))))
+
+
+(defun doc-show-inline--timer-ensure (state)
+  "Ensure the timer is enabled when STATE is non-nil, otherwise disable."
+  (cond
+    (state
+      (cond
+        (doc-show-inline--idle-timer
+          (doc-show-inline--log-info
+            "idle timer ensure t, already enabled for %S"
+            (current-buffer)))
+        (t
+          (doc-show-inline--log-info "idle timer ensure t, enabling for %S" 
(current-buffer))
+          (setq doc-show-inline--idle-timer
+            ;; One off, set repeat so the timer can be manually disabled,
+            ;; ensuring it is only disabled on successful completion.
+            ;; Pass a nil function here, set the function & arguments below.
+            (run-with-idle-timer
+              doc-show-inline-idle-delay
+              t
+              #'doc-show-inline--timer-callback-or-disable))
+
+          (timer-set-function
+            doc-show-inline--idle-timer
+            #'doc-show-inline--timer-callback-or-disable
+            (list
+              ;; Pass the timer, to allow cancellation from the timer.
+              doc-show-inline--idle-timer
+              ;; Pass the buffer (check the buffer is still active).
+              (current-buffer))))))
+
+    (t
+      (when doc-show-inline--idle-timer
+        (cancel-timer doc-show-inline--idle-timer))
+      (kill-local-variable 'doc-show-inline--idle-timer))))
+
+(defun doc-show-inline--timer-reset ()
+  "Run this when the buffer was changed."
+  ;; Ensure changing windows triggers the idle timer if this buffer uses the 
mode.
+  (when (bound-and-true-p doc-show-inline-mode)
+    (doc-show-inline--timer-ensure t)))
+
+(defun doc-show-inline--timer-buffer-local-enable ()
+  "Ensure buffer local state is enabled."
+  ;; Needed in case focus changes before the idle timer runs.
+  (doc-show-inline--timer-ensure t)
+  (add-hook 'window-state-change-hook #'doc-show-inline--timer-reset nil t))
+
+(defun doc-show-inline--timer-buffer-local-disable ()
+  "Ensure buffer local state is disabled."
+  (doc-show-inline--timer-ensure nil)
+  (remove-hook 'window-state-change-hook #'doc-show-inline--timer-reset t))
+
+
+;; ---------------------------------------------------------------------------
+;; Gap-less Font Lock Overlay Hack
+;;
+;; Unfortunately C/C++ font locking performs tricks resulting in gaps in ranges
+;; with `jit-lock-register' callbacks.
+;; This is annoying but can be worked around using
+
+(defun doc-show-inline--cc-gapless-hack-fn (old-fn beg end)
+  "Advice for `c-context-expand-fl-region' (OLD-FN),extract the region (BEG 
END)."
+  (let ((bounds (funcall old-fn beg end)))
+    (when (bound-and-true-p doc-show-inline-mode)
+      (doc-show-inline--idle-font-lock-region-pending (car bounds) (cdr 
bounds))
+      bounds)))
+
+(defun doc-show-inline--jit-or-gapless-hack-is-needed ()
+  "Check if any buffers need this hack."
+  (let ((result nil))
+    (let ((buffers (buffer-list)))
+      (while buffers
+        (let ((buf (pop buffers)))
+          (when
+            (and
+              (buffer-local-value 'doc-show-inline-mode buf)
+              (memq (buffer-local-value 'major-mode buf) 
doc-show-inline--cc-modes))
+            ;; Break.
+            (setq buffers nil)
+            (setq result t)))))
+    result))
+
+(defun doc-show-inline--jit-or-gapless-hack-set (state)
+  "Setup the callback for tracking ranges that need to be handled.
+Use STATE to enable/disable."
+  (cond
+    ((memq major-mode doc-show-inline--cc-modes)
+      (cond
+        (state
+          ;; Needed so existing regions that are highlighted will be
+          ;; calculated again with the callback installed.
+          (font-lock-flush)
+          (advice-add 'c-context-expand-fl-region :around 
#'doc-show-inline--cc-gapless-hack-fn))
+        (t
+          ;; Only remove when no other buffers use this mode.
+          (unless (doc-show-inline--jit-or-gapless-hack-is-needed)
+            (advice-remove 'c-context-expand-fl-region 
#'doc-show-inline--cc-gapless-hack-fn)))))
+
+    (t
+      (cond
+        (state
+          (jit-lock-register #'doc-show-inline--idle-font-lock-region-pending))
+        (t
+          (jit-lock-unregister 
#'doc-show-inline--idle-font-lock-region-pending))))))
+
+
+;; ---------------------------------------------------------------------------
+;; Internal Mode Logic
+
+(defun doc-show-inline--idle-enable ()
+  "Enable the idle style of updating."
+
+  (doc-show-inline--init-face-background-once)
+
+  (doc-show-inline--jit-or-gapless-hack-set t)
+
+  ;; Setup default callbacks based on mode.
+  (let ((defaults (assoc-default major-mode doc-show-inline-mode-defaults 'eq 
nil)))
+    ;; Set unless the user has set this already.
+    (unless doc-show-inline-filter
+      (setq doc-show-inline-filter (or (plist-get defaults :filter) 
'identity))))
+
+  (doc-show-inline--timer-buffer-local-enable))
+
+(defun doc-show-inline--idle-disable ()
+  "Disable the idle style of updating."
+
+  (doc-show-inline--jit-or-gapless-hack-set nil)
+
+  (doc-show-inline--overlays-remove)
+  (doc-show-inline--idle-overlays-remove)
+  (doc-show-inline--timer-buffer-local-disable)
+
+  ;; Debug only, disabled by default.
+  (when doc-show-inline--idle-overlays-debug
+    (remove-overlays (point-min) (point-max) 
'doc-show-inline-idle-overlay-debug t)))
+
+;;;###autoload
+(defun doc-show-inline-buffer ()
+  "Calculate overlays for the whole buffer."
+  (interactive)
+
+  (unless (bound-and-true-p doc-show-inline-mode)
+    (user-error "Error: doc-show-inline-mode is not active!"))
+
+  (font-lock-ensure (point-min) (point-max))
+  (doc-show-inline--idle-font-lock-region-pending (point-min) (point-max))
+  (doc-show-inline--idle-handle-pending-ranges)
+  ;; No need for the timer.
+  (doc-show-inline--timer-ensure nil))
+
+
+;; ---------------------------------------------------------------------------
+;; Define Minor Mode
+;;
+;; Developer note, use global hooks since these run before buffers are loaded.
+;; Each function checks if the local mode is active before operating.
+
+(defun doc-show-inline-mode-enable (&optional is-interactive)
+  "Turn on option `doc-show-inline-mode' for the current buffer.
+When IS-INTERACTIVE is true, use `doc-show-inline-idle-delay-init'."
+
+  (when doc-show-inline--use-lookup-cache
+    (setq doc-show-inline--lookup-cache (make-hash-table :test 'equal)))
+
+  (doc-show-inline--idle-enable)
+
+  ;; Should always be true.
+  (when doc-show-inline--idle-timer
+    ;; When loading for the first time, postpone `timer-set-idle-time',
+    ;; since `lsp-mode' may take some time to initialize.
+    ;; Otherwise this can run immediately when started on an existing buffer.
+    (timer-set-idle-time
+      doc-show-inline--idle-timer
+      (cond
+        (is-interactive
+          0.0)
+        (t
+          doc-show-inline-idle-delay-init))
+      nil)))
+
+(defun doc-show-inline-mode-disable ()
+  "Turn off option `doc-show-inline-mode' for the current buffer."
+
+  (when doc-show-inline--use-lookup-cache
+    (kill-local-variable 'doc-show-inline--lookup-cache))
+
+  (doc-show-inline--idle-disable))
+
+;;;###autoload
+(define-minor-mode doc-show-inline-mode
+  "Toggle variable `doc-show-inline-mode' in the current buffer."
+  :global nil
+
+  (cond
+    (doc-show-inline-mode
+      (unless doc-show-inline--inhibit-mode
+        (doc-show-inline-mode-enable (called-interactively-p 'interactive))))
+    (t
+      (doc-show-inline-mode-disable))))
+
+(provide 'doc-show-inline)
+;;; doc-show-inline.el ends here
diff --git a/readme.rst b/readme.rst
new file mode 100644
index 0000000000..810ab2bf03
--- /dev/null
+++ b/readme.rst
@@ -0,0 +1,148 @@
+#####################
+Emacs Doc Show Inline
+#####################
+
+Shows doc-strings inline (in the source code) for projects that contain 
doc-strings in their public headers.
+
+External doc-strings are displayed above functions & variables with syntax 
highlighting,
+with a modified background color so they are distinct from the editable code.
+
+.. figure:: 
https://gitlab.com/ideasman42/emacs-doc-show-inline/uploads/3dd58be0262c1cfb336101335bd49a02/doc-show-inline-small.png
+   :target: 
https://gitlab.com/ideasman42/emacs-doc-show-inline/uploads/167d42282f4150c95850c40784deb25b/doc-show-inline.png
+
+   Source file (left) showing public doc-stings inline (right).
+
+Available via `melpa <https://melpa.org/#/doc-show-inline>`__.
+
+
+Motivation
+==========
+
+Supporting having doc-strings always visible along side implementations,
+without having to switch files to be aware of their intended usage while 
browsing or editing a code-base.
+
+
+Usage
+=====
+
+This package provides a minor mode which can be enabled as via a mode hook or 
toggled via a key shortcut,
+which may be preferable especially for very large doc-strings which could be 
intrusive.
+
+
+Customization
+-------------
+
+``doc-show-inline-idle-delay-init`` (float ``1.0``)
+   The idle delay to use before activating for the first time.
+
+``doc-show-inline-idle-delay`` (float ``0.75``)
+   The idle delay to use before updating doc-strings.
+
+``doc-show-inline-face-background-highlight`` (float ``-0.04``)
+   The tint to use when generating the background color for the background of 
doc-string overlays.
+   The value is between -1.0 and 1.0 where negative numbers darken, positive 
numbers brighten.
+
+``doc-show-inline-face``
+   The face to use for the background (other faces get higher priority).
+
+   When left unchanged the background will be calculated based on the current 
theme using
+   ``doc-show-inline-face-background-highlight``.
+
+``doc-show-inline-use-logging`` (boolean ``nil``)
+   When non-nil, log details about lookups to ``*doc-show-inline-log*``,
+   use this to troubleshoot any issue when a doc-string can't be found 
unexpectedly.
+
+
+Advanced Customization
+----------------------
+
+``doc-show-inline-buffer-hook``
+   Run this hook when loading a new buffer.
+
+   This replaces major mode hooks as well as ``after-change-major-mode-hook``.
+   This is done to avoid enabling unnecessary minor-modes only for the purpose 
of extracting comments.
+
+``doc-show-inline-fontify-hook``
+   Run before extraction, functions take two arguments for the comment range.
+   Intended for any additional highlighting such as tags or spell checking 
text,
+   note that highlighting from overlays are also supported.
+
+
+Example
+^^^^^^^
+
+For simply extracting comments, there is no need to use either of these hooks.
+However you may want to spell check the comments or highlight tags such as 
``TODO``.
+
+The following example shows how text can be spell-checked and tags can be 
highlighted
+via the `spell-fu <https://melpa.org/#/spell-fu>`__ & `hl-prog-extra 
<https://melpa.org/#/hl-prog-extra>`__  packages.
+
+.. code-block:: elisp
+
+   ;; Enable modes that support comment highlighting.
+   (add-hook 'doc-show-inline-buffer-hook
+     (lambda ()
+       (hl-prog-extra-mode)
+       (spell-fu-mode)))
+
+   ;; Ensure the comment region is spell checked.
+   (add-hook 'doc-show-inline-fontify-hook
+     (lambda (beg end)
+       (spell-fu-region beg end)))
+
+
+Function Configuration
+----------------------
+
+These functions can overridden to adjust behavior.
+
+``doc-show-inline-filter``
+   Takes the symbol and returns non-nil if the symbol should have it's 
documentation displayed.
+   In general it's harmless to set this to ``'identity`` which wont filter out 
anything.
+
+   However some symbols such as ``#define`` statements in C/C++ don't make 
sense to handle,
+   so by default they are ignored to avoid unnecessary overhead.
+
+``doc-show-inline-locations`` (symbol ``'doc-show-inline-locations-default``)
+   A function that returns a list of points that contain symbols from the 
current buffer.
+
+   By default ``imenu`` is used for this purpose.
+
+``doc-show-inline-extract-doc`` (symbol 
``'doc-show-inline-extract-doc-default``)
+   The function to extract the doc-string given the destination buffer.
+   The buffer and point will be the destination (the header file for example).
+   The function must return a ``(BEG . END)`` cons cell representing the range 
or nil on failure.
+
+   By default this scans backwards for the comment above the function.
+
+
+Details
+=======
+
+- This package only directly depends on ``imenu`` and ``xref``,
+  so any languages that store function definitions in external files will work.
+- While there are no direct dependencies on ``lsp-mode``,
+  this has only been tested using ``lsp-mode`` with both ``ccls`` and 
``clangd`` backends.
+- Documentation overlays are added while idle.
+- Any comment before the function is considered it's doc-string,
+  *(unless it's the trailing comment of a non-blank line).*
+
+
+Installation
+============
+
+The package is `available in melpa <https://melpa.org/#/doc-show-inline>`__ as 
``doc-show-inline``.
+
+Example ``use-pacakge`` that enables for C/C++ modes.
+
+.. code-block:: elisp
+
+   (use-package doc-show-inline
+     :commands (doc-show-inline-mode)
+
+     :config
+     (define-key c-mode-map (kbd "C-;") 'doc-show-inline-mode)
+     (define-key c++-mode-map (kbd "C-;") 'doc-show-inline-mode)
+
+     :hook ((c-mode . doc-show-inline-mode)
+            (c++-mode . doc-show-inline-mode))))