[elpa] externals/uniquify-files ba4f850 07/22: In uniquify-files, add another file completion style

[Stefan Monnier]

branch: externals/uniquify-files
commit ba4f85035985d5ff2456aa4000eefaca11a034c0
Author: Stephen Leake <stephen_leake@stephe-leake.org>
Commit: Stephen Leake <stephen_leake@stephe-leake.org>

    In uniquify-files, add another file completion style
    
    * packages/uniquify-files/file-complete-root-relative.el: New file.
    * packages/uniquify-files/file-complete-root-relative-test.el: New file.
---
 file-complete-root-relative-test.el | 321 ++++++++++++++++++++++++++++
 file-complete-root-relative.el      | 414 ++++++++++++++++++++++++++++++++++++
 2 files changed, 735 insertions(+)

diff --git a/file-complete-root-relative-test.el 
b/file-complete-root-relative-test.el
new file mode 100644
index 0000000..66bdf43
--- /dev/null
+++ b/file-complete-root-relative-test.el
@@ -0,0 +1,321 @@
+;;; file-complete-root-relative-test.el - Test for 
file-complete-root-relative.el -*- lexical-binding:t no-byte-compile:t -*-
+;;
+;; Copyright (C) 2017, 2019  Free Software Foundation, Inc.
+;;
+;; Author: Stephen Leake <stephen_leake@stephe-leake.org>
+;; Maintainer: Stephen Leake <stephen_leake@stephe-leake.org>
+;;
+;; This file is part of GNU Emacs.
+;;
+;; GNU Emacs 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.
+;;
+;; GNU Emacs 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 GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
+
+(require 'ert)
+(require 'uniquify-files-test) ;; We share the test directory tree.
+(require 'file-complete-root-relative)
+
+(defconst fc-root-rel-iter (make-path-iterator :user-path-recursive (list 
uft-root)))
+
+(defconst fc-root-rel-file-list
+  (list
+    (concat uft-root "/foo-file1.text")
+    (concat uft-root "/foo-file3.texts2")
+    (concat uft-root "/Alice/alice-1/bar-file1.text")
+    (concat uft-root "/Alice/alice-1/bar-file2.text")
+    (concat uft-root "/Alice/alice-1/foo-file1.text")
+    (concat uft-root "/Alice/alice-1/foo-file2.text")
+    (concat uft-root "/Alice/alice-2/bar-file1.text")
+    (concat uft-root "/Alice/alice-2/bar-file2.text")
+    (concat uft-root "/Alice/alice-2/foo-file1.text")
+    (concat uft-root "/Alice/alice-2/foo-file3.text")
+    (concat uft-root "/Alice/alice-2/foo-file3.texts")
+    (concat uft-root "/Alice/alice-3/foo-file4.text")
+    (concat uft-root "/Bob/alice-3/foo-file4.text")
+    (concat uft-root "/Bob/bob-1/foo-file1.text")
+    (concat uft-root "/Bob/bob-1/foo-file2.text")
+    (concat uft-root "/Bob/bob-2/foo-file1.text")
+    (concat uft-root "/Bob/bob-2/foo-file5.text")
+    ))
+
+(ert-deftest test-fc-root-rel-completion-table-iter ()
+  "Test basic functions of table."
+  ;; grouped by action
+  (should (equal (fc-root-rel-completion-table-iter fc-root-rel-iter "fi" nil 
'(boundaries . ".text"))
+                  '(boundaries . (0 . 5))))
+
+  (should (equal (fc-root-rel-completion-table-iter fc-root-rel-iter "fi" nil 
'metadata)
+                (cons 'metadata
+                      (list
+                       '(category . project-file)
+                       (cons 'root uft-root)))))
+
+  ;; all-completions. We sort the results here to make the test stable
+  (should (equal (sort (fc-root-rel-completion-table-iter fc-root-rel-iter "" 
nil t) #'string-lessp)
+                (list
+                 (concat uft-alice1 "/bar-file1.text")
+                 (concat uft-alice1 "/bar-file2.text")
+                 (concat uft-alice1 "/foo-file1.text")
+                 (concat uft-alice1 "/foo-file2.text")
+                 (concat uft-alice2 "/bar-file1.text")
+                 (concat uft-alice2 "/bar-file2.text")
+                 (concat uft-alice2 "/foo-file1.text")
+                 (concat uft-alice2 "/foo-file3.text")
+                 (concat uft-alice2 "/foo-file3.texts")
+                 (concat uft-Alice-alice3 "/foo-file4.text")
+                 (concat uft-Bob-alice3 "/foo-file4.text")
+                 (concat uft-bob1 "/foo-file1.text")
+                 (concat uft-bob1 "/foo-file2.text")
+                 (concat uft-bob2 "/foo-file1.text")
+                 (concat uft-bob2 "/foo-file5.text")
+                 (concat uft-root "/foo-file1.text")
+                 (concat uft-root "/foo-file3.texts2")
+                 )))
+
+  (should (equal (sort (fc-root-rel-completion-table-iter fc-root-rel-iter 
"a-1/f-fi" nil t) #'string-lessp)
+                (list
+                 (concat uft-alice1 "/foo-file1.text")
+                 (concat uft-alice1 "/foo-file2.text")
+                 )))
+
+  (should (equal (fc-root-rel-completion-table-iter fc-root-rel-iter 
"file1.text<uft-alice1/>" nil t)
+                ;; some caller did not deuniquify; treated as misspelled; no 
match
+                nil))
+
+
+  ;; This table does not implement try-completion
+  (should (equal (fc-root-rel-completion-table-iter fc-root-rel-iter "fi" nil 
nil)
+                nil))
+
+  ;; test-completion
+  (should (equal (fc-root-rel-completion-table-iter
+                 fc-root-rel-iter
+                 (fc-root-rel-to-table-input "alice-1/foo-file1.text") nil 
'lambda)
+                nil)) ;; not at root
+
+  (should (equal (fc-root-rel-completion-table-iter
+                 fc-root-rel-iter
+                 (fc-root-rel-to-table-input "Alice/alice-1/foo-file1.text") 
nil 'lambda)
+                t)) ;; at root
+
+  )
+
+(ert-deftest test-fc-root-rel-completion-table-list ()
+  "Test basic functions of table."
+  ;; grouped by action
+  (should (equal (fc-root-rel-completion-table-list fc-root-rel-file-list 
uft-root "fi" nil '(boundaries . ".text"))
+                  '(boundaries . (0 . 5))))
+
+  (should (equal (fc-root-rel-completion-table-list fc-root-rel-file-list 
uft-root "fi" nil 'metadata)
+                (cons 'metadata
+                      (list
+                       '(category . project-file)
+                       (cons 'root uft-root)))))
+
+  ;; all-completions. We sort the results here to make the test stable
+  (should (equal (sort (fc-root-rel-completion-table-list 
fc-root-rel-file-list uft-root "" nil t) #'string-lessp)
+                (list
+                 (concat uft-alice1 "/bar-file1.text")
+                 (concat uft-alice1 "/bar-file2.text")
+                 (concat uft-alice1 "/foo-file1.text")
+                 (concat uft-alice1 "/foo-file2.text")
+                 (concat uft-alice2 "/bar-file1.text")
+                 (concat uft-alice2 "/bar-file2.text")
+                 (concat uft-alice2 "/foo-file1.text")
+                 (concat uft-alice2 "/foo-file3.text")
+                 (concat uft-alice2 "/foo-file3.texts")
+                 (concat uft-Alice-alice3 "/foo-file4.text")
+                 (concat uft-Bob-alice3 "/foo-file4.text")
+                 (concat uft-bob1 "/foo-file1.text")
+                 (concat uft-bob1 "/foo-file2.text")
+                 (concat uft-bob2 "/foo-file1.text")
+                 (concat uft-bob2 "/foo-file5.text")
+                 (concat uft-root "/foo-file1.text")
+                 (concat uft-root "/foo-file3.texts2")
+                 )))
+
+  (should (equal (sort (fc-root-rel-completion-table-list
+                       fc-root-rel-file-list uft-root "a-1/f-fi" nil t)
+                      #'string-lessp)
+                (list
+                 (concat uft-alice1 "/foo-file1.text")
+                 (concat uft-alice1 "/foo-file2.text")
+                 )))
+
+  (should (equal (fc-root-rel-completion-table-list fc-root-rel-file-list 
uft-root "uft-alice1/file1.text" nil t)
+                ;; misspelled; no match
+                nil))
+
+  ;; This table does not implement try-completion
+  (should (equal (fc-root-rel-completion-table-list fc-root-rel-file-list 
uft-root "fi" nil nil)
+                nil))
+
+  ;; test-completion
+  (should (equal (fc-root-rel-completion-table-list
+                 fc-root-rel-file-list uft-root
+                 (fc-root-rel-to-table-input "alice-1/foo-file1.text") nil 
'lambda)
+                nil)) ;; not at root
+
+  (should (equal (fc-root-rel-completion-table-iter
+                 fc-root-rel-iter
+                 (fc-root-rel-to-table-input "Alice/alice-1/foo-file1.text") 
nil 'lambda)
+                t)) ;; at root
+  )
+
+(defun test-fc-root-rel-test-completion-1 (table)
+  (should (equal (test-completion "foo-fi" table)
+                nil))
+
+  (should (equal (test-completion "dir/f-fi" table)
+                nil))
+
+  (should (equal (test-completion "foo-file1.text" table)
+                t)) ;; starts at root
+
+  (should (equal (test-completion "alice-1/foo-file1.text" table)
+                nil)) ;; does not start at root
+
+  (should (equal (test-completion "Alice/alice-1/foo-file1.text" table)
+                t)) ;; starts at root
+
+  (should (equal (test-completion "foo-file3.text" table)
+                nil))
+
+  (should (equal (test-completion "foo-file3.texts2" table)
+                t))
+
+  (should (equal (test-completion "Alice/alice-/bar-file2.text" table)
+                nil))
+
+  (should (equal (test-completion "Alice/alice-1/bar-file2.text" table)
+                t))
+  )
+
+(ert-deftest test-fc-root-rel-test-completion-iter ()
+  (let ((table (apply-partially 'fc-root-rel-completion-table-iter 
fc-root-rel-iter))
+       (completion-category-overrides '(project-file (styles . 
file-root-rel))))
+    (test-fc-root-rel-test-completion-1 table)))
+
+(ert-deftest test-fc-root-rel-test-completion-list ()
+  (let ((table (apply-partially 'fc-root-rel-completion-table-list 
fc-root-rel-file-list uft-root))
+       (completion-category-overrides '(project-file (styles . 
file-root-rel))))
+    (test-fc-root-rel-test-completion-1 table)))
+
+(defun test-fc-root-rel-all-completions-noface-1 (table)
+  (should (equal
+          (sort (fc-root-rel-all-completions "" table nil nil) #'string-lessp)
+          (list
+           "Alice/alice-1/bar-file1.text"
+           "Alice/alice-1/bar-file2.text"
+           "Alice/alice-1/foo-file1.text"
+           "Alice/alice-1/foo-file2.text"
+           "Alice/alice-2/bar-file1.text"
+           "Alice/alice-2/bar-file2.text"
+           "Alice/alice-2/foo-file1.text"
+           "Alice/alice-2/foo-file3.text"
+           "Alice/alice-2/foo-file3.texts"
+           "Alice/alice-3/foo-file4.text"
+           "Bob/alice-3/foo-file4.text"
+           "Bob/bob-1/foo-file1.text"
+           "Bob/bob-1/foo-file2.text"
+           "Bob/bob-2/foo-file1.text"
+           "Bob/bob-2/foo-file5.text"
+           "foo-file1.text"
+           "foo-file3.texts2"
+           )))
+
+  (should (equal
+          (sort (fc-root-rel-all-completions "*-fi" table nil nil) 
#'string-lessp)
+          (list
+           "Alice/alice-1/bar-file1.text"
+           "Alice/alice-1/bar-file2.text"
+           "Alice/alice-1/foo-file1.text"
+           "Alice/alice-1/foo-file2.text"
+           "Alice/alice-2/bar-file1.text"
+           "Alice/alice-2/bar-file2.text"
+           "Alice/alice-2/foo-file1.text"
+           "Alice/alice-2/foo-file3.text"
+           "Alice/alice-2/foo-file3.texts"
+           "Alice/alice-3/foo-file4.text"
+           "Bob/alice-3/foo-file4.text"
+           "Bob/bob-1/foo-file1.text"
+           "Bob/bob-1/foo-file2.text"
+           "Bob/bob-2/foo-file1.text"
+           "Bob/bob-2/foo-file5.text"
+           "foo-file1.text"
+           "foo-file3.texts2"
+           )))
+
+  (should (equal
+          (sort (fc-root-rel-all-completions "b" table nil nil) #'string-lessp)
+          nil))
+
+  (let ((completion-ignore-case t))
+    (should (equal
+            (sort (fc-root-rel-all-completions "b" table nil nil) 
#'string-lessp)
+                  (list
+                   "Bob/alice-3/foo-file4.text"
+                   "Bob/bob-1/foo-file1.text"
+                   "Bob/bob-1/foo-file2.text"
+                   "Bob/bob-2/foo-file1.text"
+                   "Bob/bob-2/foo-file5.text"
+                   )))
+    )
+
+  (should (equal
+          (sort (fc-root-rel-all-completions "*/foo" table nil nil) 
#'string-lessp)
+          (list
+           "Alice/alice-1/foo-file1.text"
+           "Alice/alice-1/foo-file2.text"
+           "Alice/alice-2/foo-file1.text"
+           "Alice/alice-2/foo-file3.text"
+           "Alice/alice-2/foo-file3.texts"
+           "Alice/alice-3/foo-file4.text"
+           "Bob/alice-3/foo-file4.text"
+           "Bob/bob-1/foo-file1.text"
+           "Bob/bob-1/foo-file2.text"
+           "Bob/bob-2/foo-file1.text"
+           "Bob/bob-2/foo-file5.text"
+           )))
+
+  (should (equal
+          (sort (fc-root-rel-all-completions "Alice/alice-1/" table nil nil) 
#'string-lessp)
+          (list
+           "Alice/alice-1/bar-file1.text"
+           "Alice/alice-1/bar-file2.text"
+           "Alice/alice-1/foo-file1.text"
+           "Alice/alice-1/foo-file2.text"
+           )))
+
+  (should (equal
+          (sort (fc-root-rel-all-completions "Alice/alice-1/f-file2" table nil 
nil) #'string-lessp)
+          (list
+           "Alice/alice-1/foo-file2.text"
+           )))
+  )
+
+(ert-deftest test-fc-root-rel-all-completions-noface-iter ()
+  (let ((table (apply-partially 'fc-root-rel-completion-table-iter 
fc-root-rel-iter))
+       (completion-category-overrides '(project-file (styles . file-root-rel)))
+       (completion-ignore-case nil))
+    (test-fc-root-rel-all-completions-noface-1 table)))
+
+(ert-deftest test-fc-root-rel-all-completions-noface-list ()
+  (let ((table (apply-partially 'fc-root-rel-completion-table-list 
fc-root-rel-file-list uft-root))
+       (completion-category-overrides '(project-file (styles . file-root-rel)))
+       (completion-ignore-case nil))
+    (test-fc-root-rel-all-completions-noface-1 table)))
+
+;; FIXME: more tests
+
+(provide 'file-complete-root-relative-test)
+;;; file-complete-root-relative-test.el ends here
diff --git a/file-complete-root-relative.el b/file-complete-root-relative.el
new file mode 100644
index 0000000..86b1459
--- /dev/null
+++ b/file-complete-root-relative.el
@@ -0,0 +1,414 @@
+;;; file-complete-root-relative.el --- Completion style for files  -*- 
lexical-binding:t -*-
+;;
+;; Copyright (C) 2019 Free Software Foundation, Inc.
+;;
+;; Author: Stephen Leake <stephen_leake@stephe-leake.org>
+;; Maintainer: Stephen Leake <stephen_leake@stephe-leake.org>
+;; Keywords: completion
+;; Version: 0
+;; package-requires: ((emacs "25.0"))
+;;
+;; This file is part of GNU Emacs.
+;;
+;; GNU Emacs 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.
+;;
+;; GNU Emacs 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 GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
+
+
+;;; Commentary
+
+;; A file completion style in which the root directory is left out of
+;; the completion string displayed to the user.
+;;
+;; Following the Design section in uniquify-files.el, this completion
+;; style has the following string formats:
+;;
+;; - user: file name relative to a root directory
+;;
+;; - completion table input: same as user
+;;
+;; - data: absolute file name
+;;
+;; The completion style requires knowlege of the root directory;
+;; currently, this requires use of a completion function to provide a
+;; place to store it.
+
+(require 'cl-lib)
+
+(require 'uniquify-files);; FIXME: we share many low-level functions; factor 
them out.
+
+(defun fc-root-rel--root (table)
+  "Return root from TABLE."
+  (cdr (assoc 'root (completion-metadata "" table nil))))
+
+(defun fc-root-rel-to-table-input (user-string)
+  "Implement `completion-to-table-input' for file-root-rel."
+  user-string)
+
+(defun fc-root-rel-to-data (user-string table _pred)
+  "Implement `completion-get-data-string' for file-root-rel."
+  ;; We assume USER-STRING is complete and unique.
+  (let ((root (fc-root-rel--root table)))
+    (concat root user-string)))
+
+(defun fc-root-rel-to-user (data-string-list root)
+  "Convert DATA-STRING-LIST to list of user format strings."
+  ;; Assume they all start with ROOT
+  (let ((prefix-length (1+ (length root)))) ;; don't include leading '/'
+    (mapcar
+     (lambda (abs-file-name)
+       (substring abs-file-name prefix-length))
+     data-string-list)
+  ))
+
+(defun fc-root-rel--pcm-merged-pat (string all point)
+  "Return a pcm pattern that is the merged completion of STRING in ALL.
+ALL must be a list of table input format strings?
+Pattern is in reverse order."
+  (let* ((case-fold-search completion-ignore-case)
+        (completion-pcm--delim-wild-regex
+         (concat "[" completion-pcm-word-delimiters "*]"))
+        (pattern (completion-pcm--string->pattern string point)))
+    (completion-pcm--merge-completions all pattern)
+    ))
+
+(defun fc-root-rel-try-completion (string table pred point)
+  "Implement `completion-try-completion' for file-root-rel."
+  ;; Returns list of user format strings (uniquified file names), nil, or t.
+  (let (result
+       rel-all
+       done)
+
+    ;; Compute result, set done.
+    (cond
+     ((functionp table)
+      (setq rel-all (fc-root-rel-all-completions string table pred point))
+
+      (cond
+       ((null rel-all) ;; No matches.
+       (setq result nil)
+       (setq done t))
+
+       ((= 1 (length rel-all)) ;; One match; unique.
+       (setq done t)
+
+       ;; Check for valid completion
+       (if (string-equal string (car rel-all))
+           (setq result t)
+
+         (setq result (car rel-all))
+         (setq result (cons result (length result)))))
+
+       (t ;; Multiple matches
+       (setq done nil))
+       ))
+
+     ;; The following cases handle being called from
+     ;; icomplete-completions with the result of `all-completions'
+     ;; instead of the real table function. TABLE is a list of
+     ;; relative file names.
+
+     ((null table) ;; No matches.
+      (setq result nil)
+      (setq done t))
+
+     (t
+      (setq rel-all table)
+      (setq done nil))
+     )
+
+    (if done
+       result
+
+      ;; Find merged completion of relative file names
+      (let* ((merged-pat (fc-root-rel--pcm-merged-pat string rel-all point))
+
+            ;; `merged-pat' is in reverse order.  Place new point at:
+            (point-pat (or (memq 'point merged-pat) ;; the old point
+                           (memq 'any   merged-pat) ;; a place where there's 
something to choose
+                           (memq 'star  merged-pat) ;; ""
+                           merged-pat))             ;; the end
+
+            ;; `merged-pat' does not contain 'point when the field
+            ;; containing 'point is fully completed.
+
+            (new-point (length (completion-pcm--pattern->string point-pat)))
+
+            ;; Compute this after `new-point' because `nreverse'
+            ;; changes `point-pat' by side effect.
+            (merged (completion-pcm--pattern->string (nreverse merged-pat))))
+
+       (cons merged new-point)))
+   ))
+
+(defun fc-root-rel--hilit (string all point)
+  "Apply face text properties to each element of ALL.
+STRING is the current user input.
+ALL is a list of strings in user format.
+POINT is the position of point in STRING.
+Returns new list.
+
+Adds the face `completions-first-difference' to the first
+character after each completion field."
+  (let* ((merged-pat (nreverse (fc-root-rel--pcm-merged-pat string all point)))
+        (field-count 0)
+        (regex (completion-pcm--pattern->regex merged-pat '(any star any-delim 
point)))
+        )
+    (dolist (x merged-pat)
+      (when (not (stringp x))
+       (setq field-count (1+ field-count))))
+
+    (mapcar
+     (lambda (str)
+       (when (string-match regex str)
+        (cl-loop
+         for i from 1 to field-count
+         do
+         (when (and
+                (match-beginning i)
+                (<= (1+ (match-beginning i)) (length str)))
+           (put-text-property (match-beginning i) (1+ (match-beginning i)) 
'face 'completions-first-difference str))
+         ))
+       str)
+     all)))
+
+(defun fc-root-rel-all-completions (user-string table pred point)
+  "Implement `completion-all-completions' for uniquify-file."
+  ;; Returns list of data format strings (abs file names).
+
+  (let* ((table-string (fc-root-rel-to-table-input user-string))
+        (all (funcall table table-string pred t)))
+
+    (when all
+      (setq all (fc-root-rel-to-user all (fc-root-rel--root table)))
+      (fc-root-rel--hilit user-string all point))
+    ))
+
+(defun fc-root-rel--valid-completion (string all root)
+  "Return non-nil if STRING is a valid completion in ALL,
+else return nil.  ALL should be the result of `all-completions'.
+STRING should be in completion table input format."
+  (let* ((abs-string (concat root "/" string))
+        (matched nil)
+        name)
+
+    (while (and all
+               (not matched))
+      (setq name (pop all))
+      (when (string-equal abs-string name)
+       (setq matched t)))
+
+    matched))
+
+(defun fc-root-rel--pcm-pattern-iter (string root)
+  "Return pcm regexes constructed from STRING (a table format string)."
+  ;; In file-name-all-completions, `completion-regexp-list', is
+  ;; matched against file names and directories relative to `dir'.
+  ;; Thus to handle partial completion delimiters in `string', we
+  ;; construct two regexps from `string'; one from the directory
+  ;; portion, and one from the non-directory portion.
+  (let ((file-name (file-name-nondirectory string))
+       (dir-name (directory-file-name (or (file-name-directory string) "")))
+       dir-length)
+
+    (setq dir-length (length dir-name))
+
+    (when (and (< 0 (length file-name))
+              (= ?* (aref file-name 0)))
+      (setq dir-name (concat dir-name "*")))
+
+    ;; `completion-pcm--string->pattern' assumes its argument is
+    ;; anchored at the beginning but not the end; that is true
+    ;; for `dir-name' once we prepend ROOT.  file-name must match
+    ;; a directory in "root/dir-name".
+    (let* ((dir-pattern (completion-pcm--string->pattern dir-name))
+          (file-pattern (completion-pcm--string->pattern string))
+          (dir-regex
+           (cond
+            ((= 0 (length dir-name))
+             (if (= 0 (length file-name))
+                 root
+               (concat root
+                       "\\(\\'\\|/"
+                       (substring (completion-pcm--pattern->regex 
file-pattern) 2) ;; strip \`
+                       "\\)")))
+
+            ((string-equal "*" dir-name)
+             (if (or (= 0 dir-length)
+                     (= 0 (length file-name)))
+                 (concat root "/?")
+
+               ;; else STRING contains an explicit "/"
+               (concat root "/")))
+
+            (t
+             (concat root
+                     "/"
+                     (substring (completion-pcm--pattern->regex dir-pattern) 2)
+                     "\\("
+                     (substring (completion-pcm--pattern->regex file-pattern) 
2)
+                     "\\)?"))
+            ))
+
+          ;; file-regex is matched against an absolute file name
+          (file-regex
+           (concat root
+                   (if (eq 'star (nth 0 file-pattern)) "/?" "/")
+                   (substring (completion-pcm--pattern->regex file-pattern) 
2)))
+          )
+      (list dir-regex file-regex))))
+
+(defun fc-root-rel-completion-table-iter (path-iter string pred action)
+  "Implement a completion table for file names in PATH-ITER.
+
+PATH-ITER is a `path-iterator' object; it must have exacly one
+recursive root, and no non-recursive roots.
+
+STRING, PRED, ACTION are completion table arguments."
+
+  ;; This completion table function combines iterating on files in
+  ;; PATH-ITER with filtering on USER-STRING and PRED. This is an
+  ;; optimization that minimizes storage use when USER-STRING is not
+  ;; empty and PRED is non-nil.
+
+  (cond
+   ((eq (car-safe action) 'boundaries)
+    ;; We don't use boundaries; return the default definition.
+    (cons 'boundaries
+         (cons 0 (length (cdr action)))))
+
+   ((eq action 'metadata)
+    (cons 'metadata
+         (list
+          ;; We specify the category 'project-file here, to match the
+          ;; `completion-category-defaults' setting above.  We use
+          ;; the default sort order, which is shortest first, so
+          ;; "project.el" is easier to complete when it also matches
+          ;; "project-am.el".
+          '(category . project-file)
+          (cons 'root (car (path-iter-path-recursive-init path-iter))))))
+
+   ((null action)
+    ;; Called from `try-completion'; should never get here (see
+    ;; `fc-root-rel-try-completion').
+    nil)
+
+   ((memq action
+         '(lambda ;; Called from `test-completion'
+            t))   ;; Called from all-completions
+
+    ;; In file-name-all-completions, `completion-regexp-list', is
+    ;; matched against file names and directories relative to `dir',
+    ;; which is useless for this table.
+
+    (pcase-let ((`(,dir-regex ,file-regex)
+                (fc-root-rel--pcm-pattern-iter string (car 
(path-iter-path-recursive-init path-iter)))))
+      (let ((result nil)
+           (case-fold-search completion-ignore-case)
+           dir)
+
+       (path-iter-restart path-iter)
+       (while (setq dir (path-iter-next path-iter))
+         (when (string-match dir-regex dir)
+           (cl-mapc
+            (lambda (file-name)
+              (let ((absfile (concat (file-name-as-directory dir) file-name)))
+                (when (and (not (string-equal "." (substring absfile -1)))
+                           (not (string-equal ".." (substring absfile -2)))
+                           (not (file-directory-p absfile))
+                           (string-match file-regex absfile)
+                           (or (null pred)
+                               (funcall pred absfile)))
+                  (push absfile result))))
+            (directory-files dir))
+           ))
+       (cond
+        ((eq action 'lambda)
+         ;; Called from `test-completion'
+         (fc-root-rel--valid-completion string result (car 
(path-iter-path-recursive-init path-iter))))
+
+        ((eq action t)
+         ;; Called from all-completions
+         result)
+        ))
+      ))
+   ))
+
+(defun fc-root-rel--pcm-pattern-list (string root)
+  "Return pcm regex constructed from STRING (a table format string)."
+  (let ((pattern (completion-pcm--string->pattern string)))
+    (concat "\\`"
+           root
+           (when (< 0 (length string)) "/")
+           (substring (completion-pcm--pattern->regex pattern) 2);; trim \`
+           )))
+
+(defun fc-root-rel-completion-table-list (file-list root string pred action)
+  "Implement a completion table for file names in FILE-LIST,
+with common prefix ROOT.
+
+STRING, PRED, ACTION are completion table arguments."
+
+  ;; This completion table function is required to provide access to
+  ;; ROOT via metadata.
+
+  (cond
+   ((eq (car-safe action) 'boundaries)
+    ;; We don't use boundaries; return the default definition.
+    (cons 'boundaries
+         (cons 0 (length (cdr action)))))
+
+   ((eq action 'metadata)
+    (cons 'metadata
+         (list
+          ;; We specify the category 'project-file here, to match the
+          ;; `completion-category-defaults' setting above.  We use
+          ;; the default sort order, which is shortest first, so
+          ;; "project.el" is easier to complete when it also matches
+          ;; "project-am.el".
+          '(category . project-file)
+          (cons 'root root))))
+
+   ((null action)
+    ;; Called from `try-completion'; should never get here (see
+    ;; `fc-root-rel-try-completion').
+    nil)
+
+   ((memq action
+         '(lambda ;; Called from `test-completion'
+            t))   ;; Called from all-completions
+
+    (let ((regex (fc-root-rel--pcm-pattern-list string root))
+         (result nil)
+         (case-fold-search completion-ignore-case))
+
+      (cl-mapc
+       (lambda (absfile)
+        (when (and (string-match regex absfile)
+                   (or (null pred)
+                       (funcall pred absfile)))
+          (push absfile result)))
+       file-list)
+
+      (cond
+       ((eq action 'lambda)
+       ;; Called from `test-completion'
+       (fc-root-rel--valid-completion string result root))
+
+       ((eq action t)
+       ;; Called from all-completions
+       result)
+       )))
+   ))
+
+(provide 'file-complete-root-relative)
+;;; file-complete-root-relative.el ends here