Consolidate 'widen' calls

* lisp/progmodes/prog-mode.el (prog-indentation-context):
Un-document all elements but the first.
(prog-widen): Remove.
(http://lists.gnu.org/archive/html/emacs-devel/2017-12/msg00321.html)

* doc/lispref/text.texi (Mode-Specific Indent): Update.

* lisp/progmodes/ruby-mode.el (ruby-calculate-indent):
Don't call widen.

* lisp/progmodes/python.el
(python-indent-guess-indent-offset)
(python-info-current-defun): Replace prog-widen with widen;
these functions are not called during indentation.
(python-indent-context)
(python-indent--calculate-indentation)
(python-info-dedenter-opening-block-message)
(python-info-line-ends-backslash-p)
(python-info-beginning-of-backslash)
(python-info-continuation-line-p)
(python-info-current-defun): Remove 'widen' calls.

* lisp/indent.el (indent-according-to-mode)
(indent-for-tab-command, indent-region): Move them here.

* lisp/textmodes/mhtml-mode.el (mhtml-indent-line):
Bind prog-indentation-context to one-element list.

7 files changed, 35 insertions, 125 deletions

diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index 1e19f75d682..67a303a5994 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -2396,57 +2396,31 @@ text at point (@pxref{Completion in Buffers}).
 syntax belongs to a different major mode.  Examples include
 @dfn{literate programming} source files that combine documentation and
 snippets of source code, Yacc/Bison programs that include snippets of
-plain C code, etc.  To correctly indent the embedded chunks, the major
+plain C code, etc.  To correctly indent the embedded chunks, the primary
 mode needs to delegate the indentation to another mode's indentation
 engine (e.g., call @code{c-indent-defun} for C code or
 @code{python-indent-line} for Python), while providing it with some
-context to guide the indentation.  The following facilities support
-such multi-mode indentation.
+context to guide the indentation.  Major modes, for their part, should
+avoid calling @code{widen} in their indentation code and obey
+@code{prog-first-column}.
 
 @defvar prog-indentation-context
 This variable, when non-@code{nil}, holds the indentation context for
 the sub-mode's indentation engine provided by the superior major mode.
-The value should be a list of the form @code{(@var{first-column}
-@w{(@var{start} . @var{end})} @code{prev-chunk})}.  The members of the
-list have the following meaning:
+The value should be a list of the form @code{(@var{first-column} . @var{rest}}.
+The members of the list have the following meaning:
 
 @table @var
 @item first-column
 The column to be used for top-level constructs.  This replaces the
 default value of the top-level column used by the sub-mode, usually
 zero.
-@item start
-@itemx end
-The region of the code chunk to be indented by the sub-mode.  The
-value of @var{end} can be @code{nil}, which stands for the value of
-@code{point-max}.
-@item prev-chunk
-If this is non-@code{nil}, it should provide the sub-mode's
-indentation engine with a virtual context of the code chunk.  Valid
-values include:
-
-@itemize @minus
-@item
-A string whose contents is the text the sub-mode's indentation engine
-should consider to precede the code chunk.  The sub-mode's indentation
-engine can add text properties to that string, to be reused in
-repeated calls with the same string, thus using it as a cache.  An
-example where this is useful is code chunks that need to be indented
-as function bodies, but lack the function's preamble---the string
-could then include that missing preamble.
-@item
-A function.  It is expected to be called with the start position of
-the current chunk, and should return a cons cell
-@w{@code{(@var{prev-start} . @var{prev-end})}} that specifies the
-region of the previous code chunk, or @code{nil} if there is no previous
-chunk.  This is useful in literate-programming sources, where code is
-split into chunks, and correct indentation needs to access previous
-chunks.
-@end itemize
+@item rest
+This value is currently unused.
 @end table
 @end defvar
 
-The following convenience functions should be used by major mode's
+The following convenience function should be used by major mode's
 indentation engine in support of invocations as sub-modes of another
 major mode.
 
@@ -2457,16 +2431,6 @@ function's value is the column number to use for top-level constructs.
 When no superior mode is in effect, this function returns zero.
 @end defun
 
-@defun prog-widen
-Call this function instead of @code{widen} to remove any restrictions
-imposed by the mode's indentation engine and restore the restrictions
-recorded in @code{prog-indentation-context}.  This prevents the
-indentation engine of a sub-mode from inadvertently operating on text
-outside of the chunk it was supposed to indent, and preserves the
-restriction imposed by the superior mode.  When no superior mode is in
-effect, this function just calls @code{widen}.
-@end defun
-
 
 @node Region Indent
 @subsection Indenting an Entire Region
diff --git a/etc/NEWS b/etc/NEWS
index 4ccf468693c..eb076c943bc 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1107,11 +1107,11 @@ This allows better indentation support in modes that support multiple
 programming languages in the same buffer, like literate programming
 environments or ANTLR programs with embedded Python code.
 
-A major mode can provide indentation context for a sub-mode through
-the 'prog-indentation-context' variable.  To support this, modes that
-provide indentation should use 'prog-widen' instead of 'widen' and
-'prog-first-column' instead of a literal zero.  See the node
-"(elisp) Mode-Specific Indent" in the ELisp manual for more details.
+A major mode can provide indentation context for a sub-mode.  To
+support this, modes should use 'prog-first-column' instead of a
+literal zero and never call 'widen' in their indentation functions.
+See the node "(elisp) Mode-Specific Indent" in the ELisp manual for
+more details.
 
 ** ERC
 
diff --git a/lisp/indent.el b/lisp/indent.el
index d5ba0bd8491..ccf0e99c08b 100644
--- a/lisp/indent.el
+++ b/lisp/indent.el
@@ -69,6 +69,8 @@ variable is `indent-relative' or `indent-relative-maybe', handle
 it specially (since those functions are used for tabbing); in
 that case, indent by aligning to the previous non-blank line."
   (interactive)
+  (save-restriction
+    (widen)
   (syntax-propertize (line-end-position))
   (if (memq indent-line-function
             '(indent-relative indent-relative-maybe))
@@ -84,7 +86,7 @@ that case, indent by aligning to the previous non-blank line."
             (indent-line-to column)
           (save-excursion (indent-line-to column))))
     ;; The normal case.
-    (funcall indent-line-function)))
+    (funcall indent-line-function))))
 
 (defun indent--default-inside-comment ()
   (unless (or (> (current-column) (current-indentation))
@@ -144,7 +146,9 @@ prefix argument is ignored."
           (indent--default-inside-comment)
           (when (or (<= (current-column) (current-indentation))
                     (not (eq tab-always-indent 'complete)))
-            (funcall (default-value 'indent-line-function))))
+            (save-restriction
+              (widen)
+              (funcall (default-value 'indent-line-function)))))
 
       (cond
        ;; If the text was already indented right, try completion.
@@ -538,7 +542,9 @@ column to indent to; if it is nil, use one of the three methods above."
           (forward-line 1)))))
    ;; Use indent-region-function is available.
    (indent-region-function
-    (funcall indent-region-function start end))
+    (save-restriction
+      (widen)
+      (funcall indent-region-function start end)))
    ;; Else, use a default implementation that calls indent-line-function on
    ;; each line.
    (t (indent-region-line-by-line start end)))
diff --git a/lisp/progmodes/prog-mode.el b/lisp/progmodes/prog-mode.el
index f727e458b2b..4efe443fba8 100644
--- a/lisp/progmodes/prog-mode.el
+++ b/lisp/progmodes/prog-mode.el
@@ -54,7 +54,7 @@
 
 There are languages where part of the code is actually written in
 a sub language, e.g., a Yacc/Bison or ANTLR grammar also consists
-of plain C code.  This variable enables the major mode of the
+of plain C code.  This variable enables the primary mode of the
 main language to use the indentation engine of the sub-mode for
 lines in code chunks written in the sub-mode's language.
 
@@ -64,37 +64,13 @@ mode, it should bind this variable to non-nil around the call.
 
 The non-nil value should be a list of the form:
 
-   (FIRST-COLUMN (START . END) PREVIOUS-CHUNKS)
+   (FIRST-COLUMN . REST)
 
 FIRST-COLUMN is the column the indentation engine of the sub-mode
 should use for top-level language constructs inside the code
 chunk (instead of 0).
 
-START and END specify the region of the code chunk.  END can be
-nil, which stands for the value of `point-max'.  The function
-`prog-widen' uses this to restore restrictions imposed by the
-sub-mode's indentation engine.
-
-PREVIOUS-CHUNKS, if non-nil, provides the indentation engine of
-the sub-mode with the virtual context of the code chunk.  Valid
-values are:
-
- - A string containing text which the indentation engine can
-   consider as standing in front of the code chunk.  To cache the
-   string's calculated syntactic information for repeated calls
-   with the same string, the sub-mode can add text-properties to
-   the string.
-
-   A typical use case is for grammars with code chunks which are
-   to be indented like function bodies -- the string would contain
-   the corresponding function preamble.
-
- - A function, to be called with the start position of the current
-   chunk.  It should return either the region of the previous chunk
-   as (PREV-START . PREV-END), or nil if there is no previous chunk.
-
-   A typical use case are literate programming sources -- the
-   function would successively return the previous code chunks.")
+REST is currently unused.")
 
 (defun prog-indent-sexp (&optional defun)
   "Indent the expression after point.
@@ -113,23 +89,6 @@ instead."
   "Return the indentation column normally used for top-level constructs."
   (or (car prog-indentation-context) 0))
 
-(defun prog-widen ()
-  "Remove restrictions (narrowing) from current code chunk or buffer.
-This function should be used instead of `widen' in any function used
-by the indentation engine to make it respect the value of
-`prog-indentation-context'.
-
-This function (like `widen') is useful inside a
-`save-restriction' to make the indentation correctly work when
-narrowing is in effect."
-  (let ((chunk (cadr prog-indentation-context)))
-    (if chunk
-        ;; No call to `widen' is necessary here, as narrow-to-region
-        ;; changes (not just narrows) the existing restrictions
-        (narrow-to-region (car chunk) (or (cdr chunk) (point-max)))
-      (widen))))
-
-
 (defvar-local prettify-symbols-alist nil
   "Alist of symbol prettifications.
 Each element looks like (SYMBOL . CHARACTER), where the symbol
diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index d4226e5ce7b..b8926529d1e 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -287,10 +287,6 @@
 ;;; 24.x Compat
 
 
-(unless (fboundp 'prog-widen)
-  (defun prog-widen ()
-    (widen)))
-
 (unless (fboundp 'prog-first-column)
   (defun prog-first-column ()
     0))
@@ -785,7 +781,7 @@ work on `python-indent-calculate-indentation' instead."
   (interactive)
   (save-excursion
     (save-restriction
-      (prog-widen)
+      (widen)
       (goto-char (point-min))
       (let ((block-end))
         (while (and (not block-end)
@@ -883,8 +879,6 @@ keyword
 :at-dedenter-block-start
  - Point is on a line starting a dedenter block.
  - START is the position where the dedenter block starts."
-  (save-restriction
-    (prog-widen)
     (let ((ppss (save-excursion
                   (beginning-of-line)
                   (syntax-ppss))))
@@ -1022,7 +1016,7 @@ keyword
                       (looking-at (python-rx block-ender)))
                     :after-block-end)
                    (t :after-line))
-             (point)))))))))
+             (point))))))))
 
 (defun python-indent--calculate-indentation ()
   "Internal implementation of `python-indent-calculate-indentation'.
@@ -1030,8 +1024,6 @@ May return an integer for the maximum possible indentation at
 current context or a list of integers.  The latter case is only
 happening for :at-dedenter-block-start context since the
 possibilities can be narrowed to specific indentation points."
-  (save-restriction
-    (prog-widen)
     (save-excursion
       (pcase (python-indent-context)
         (`(:no-indent . ,_) (prog-first-column)) ; usually 0
@@ -1081,7 +1073,7 @@ possibilities can be narrowed to specific indentation points."
         (`(,(or :inside-paren-newline-start-from-block) . ,start)
          ;; Add two indentation levels to make the suite stand out.
          (goto-char start)
-         (+ (current-indentation) (* python-indent-offset 2)))))))
+         (+ (current-indentation) (* python-indent-offset 2))))))
 
 (defun python-indent--calculate-levels (indentation)
   "Calculate levels list given INDENTATION.
@@ -4590,7 +4582,7 @@ Optional argument INCLUDE-TYPE indicates to include the type of the defun.
 This function can be used as the value of `add-log-current-defun-function'
 since it returns nil if point is not inside a defun."
   (save-restriction
-    (prog-widen)
+    (widen)
     (save-excursion
       (end-of-line 1)
       (let ((names)
@@ -4788,12 +4780,10 @@ likely an invalid python file."
   "Message the first line of the block the current statement closes."
   (let ((point (python-info-dedenter-opening-block-position)))
     (when point
-      (save-restriction
-        (prog-widen)
         (message "Closes %s" (save-excursion
                                (goto-char point)
                                (buffer-substring
-                                (point) (line-end-position))))))))
+                                (point) (line-end-position)))))))
 
 (defun python-info-dedenter-statement-p ()
   "Return point if current statement is a dedenter.
@@ -4809,8 +4799,6 @@ statement."
   "Return non-nil if current line ends with backslash.
 With optional argument LINE-NUMBER, check that line instead."
   (save-excursion
-    (save-restriction
-      (prog-widen)
       (when line-number
         (python-util-goto-line line-number))
       (while (and (not (eobp))
@@ -4819,14 +4807,12 @@ With optional argument LINE-NUMBER, check that line instead."
                   (not (equal (char-before (point)) ?\\)))
         (forward-line 1))
       (when (equal (char-before) ?\\)
-        (point-marker)))))
+        (point-marker))))
 
 (defun python-info-beginning-of-backslash (&optional line-number)
   "Return the point where the backslashed line start.
 Optional argument LINE-NUMBER forces the line number to check against."
   (save-excursion
-    (save-restriction
-      (prog-widen)
       (when line-number
         (python-util-goto-line line-number))
       (when (python-info-line-ends-backslash-p)
@@ -4835,15 +4821,13 @@ Optional argument LINE-NUMBER forces the line number to check against."
                  (python-syntax-context 'paren))
           (forward-line -1))
         (back-to-indentation)
-        (point-marker)))))
+        (point-marker))))
 
 (defun python-info-continuation-line-p ()
   "Check if current line is continuation of another.
 When current line is continuation of another return the point
 where the continued line ends."
   (save-excursion
-    (save-restriction
-      (prog-widen)
       (let* ((context-type (progn
                              (back-to-indentation)
                              (python-syntax-context-type)))
@@ -4869,7 +4853,7 @@ where the continued line ends."
                (python-util-forward-comment -1)
                (when (and (equal (1- line-start) (line-number-at-pos))
                           (python-info-line-ends-backslash-p))
-                 (point-marker))))))))
+                 (point-marker)))))))
 
 (defun python-info-block-continuation-line-p ()
   "Return non-nil if current line is a continuation of a block."
diff --git a/lisp/progmodes/ruby-mode.el b/lisp/progmodes/ruby-mode.el
index dc1b0f8e2da..7c101143347 100644
--- a/lisp/progmodes/ruby-mode.el
+++ b/lisp/progmodes/ruby-mode.el
@@ -1364,7 +1364,6 @@ delimiter."
                                              "\\)\\>")))
                     (eq (ruby-deep-indent-paren-p t) 'space)
                     (not (bobp)))
-                   (widen)
                    (goto-char (or begin parse-start))
                    (skip-syntax-forward " ")
                    (current-column))
diff --git a/lisp/textmodes/mhtml-mode.el b/lisp/textmodes/mhtml-mode.el
index 09da155f487..79c1125ff62 100644
--- a/lisp/textmodes/mhtml-mode.el
+++ b/lisp/textmodes/mhtml-mode.el
@@ -341,9 +341,7 @@ This is used by `mhtml--pre-command'.")
              ((eq mhtml-tag-relative-indent 'ignore)
               (setq base-indent 0)))
             (narrow-to-region region-start (point-max))
-            (let ((prog-indentation-context (list base-indent
-                                                  (cons (point-min) nil)
-                                                  nil)))
+            (let ((prog-indentation-context (list base-indent)))
               (mhtml--with-locals submode
                 ;; indent-line-function was rebound by
                 ;; mhtml--with-locals.