get_chunk_row() and get_chunk_leftedge() now become wrappers around
get_chunk(); the latter is only used directly in place_the_cursor()
when we need to get both the row and the leftedge.  get_chunk() now
uses the proper formula to implement varying chunk width.

Since chunk width now varies, place_the_cursor() sets the x position
relative to the leftedge in a different way that works regardless
of chunk width, update_softwrapped_line() loops until it gets all
softwrap breakpoints instead of calculating the full length in
advance and getting one full row at a time, the chunk iterators
now count leftedges instead of rows, and fix_firstcolumn() does a
full recalculation of the chunk that firstcolumn is on instead of
simply shifting it back.

Also, in update_softwrapped_line(), when a line's softwrap breakpoint
is before the last column of the edit window, a ">" is now added to
the end of it.

The workaround in place_the_cursor() for when two-column characters
straddle the edge of the screen is removed, as it's no longer needed
now that chunks end before such characters.

Furthermore, do_home() and do_end() use xplustabs() instead of
placewewant again when calculating the leftedge, since placewewant
refers to a column that may or may not be available (if it's not,
the cursor will be placed wrongly).  Make get_edge_and_target() use
xplustabs() instead of placewewant for the same reason; this also lets
us simplify get_edge_and_target(), since xplustabs() will never be
greater than strlenpt().  Finally, since do_end() now has to calculate
rightedge as well as rightedge_x, use the former to implement the same
time-saving optimizations as in do_home().

The cursor is not yet adjusted when we try to go directly to a column
past the end of a softwrap breakpoint, and placewewant handling in the
vertical movement code is not yet adjusted for varying chunk lengths,
but fixes for these are forthcoming.

This fixes https://savannah.gnu.org/bugs/?49440.

get_chunk_row() replaces the formula "column / editwincols".

get_chunk_leftedge() replaces "(column / editwincols) * editwincols".

get_last_chunk_row() replaces "strlenpt() / editwincols".

get_last_chunk_leftedge() replaces "(strlenpt() / editwincols) * editwincols".

This prepares us for any changes in those formulas, and for more such
functions later.

The new function find_softwrap_breakpoint() returns the column number
of the last position in screen range where we can wrap the given text
without breaking a two-column character in half (as was done until now).
The returned column number is the leftedge of the next softwrapped chunk.

If the end of the text is reached while searching for a wrapping point,
the parameter end_of_line is set to TRUE.

The new function get_chunk() uses find_softwrap_breakpoint() to find the
row and leftedge corresponding to a given column of a given line.

When also --nohelp is active and the terminal is so narrow that the
message that --constantshow displays on the bottom row does not fit,
this causes the cursor to be pushed "offscreen".  Some terminal
emulators don't handle this case correctly, and leave the cursor
in an invisible or mistaken position.  Compensate for this by
moving the cursor back to the start of the row.

This fixes https://savannah.gnu.org/bugs/?51335

.
Reported-by: David Lawrence Ramsey <pooka109@gmail.com>

This fixes a secondary part of https://savannah.gnu.org/bugs/?51124.

When receiving a SIGCONT, don't call regenerate_screen() directly
but act as if a SIGWINCH occurred.  Also insert a dummy key, and
thus let the relevant input routine redraw the relevant subwindows.

Use KEY_F0 as the dummy key, as both Ncurses and Slang know it, and
it should normally do nothing at all.

This fixes https://savannah.gnu.org/bugs/?51124.

When we are in the file browser, browser_refresh() will take care of
redrawing the title bar and the file list, so total_refresh() should
leave those two subwindows alone in that case.

This fixes https://savannah.gnu.org/bugs/?51147.

Achieve this by making the suppression flag global, so that we can
just reset it instead of making an improper call of do_cursorpos().

This fixes the secondary part of https://savannah.gnu.org/bugs/?51134.

Also, remove a useless assert.

This fixes https://savannah.gnu.org/bugs/?51134.

When spotlighting the string to be replaced, placewewant isn't valid,
so tell place_the_cursor() to ignore its value to avoid the cursor
getting mistakenly placed at the beginning of the next row.

This fixes https://savannah.gnu.org/bugs/?50997

.
Reported-by: David Lawrence Ramsey <pooka109@gmail.com>

Also, allow Ctrl+Left/Right with --enable-tiny --enable-browser.

Add missing spaces, remove excess spaces, and
replace groups of indentation spaces with tabs.

When the editing space gets narrower, either by toggling line numbers on
or making nano's window smaller, and when the cursor is near the bottom,
it can be pushed offscreen.  In that case, don't get it back onscreen by
centering the current line but by putting it on the bottom row.  This
makes for a smoother experience.

This fixes http://savannah.gnu.org/bugs/?50933.

Also, trim some comments and avoid an unused-variable warning.

Also, reshuffle two initializations to go sit with the other ones.

This avoids https://savannah.gnu.org/bugs/?49912 while at the same time
avoiding to draw the edit window twice in a row -- the first drawing
would use a wrong margin, which results in a visible and irritating
shift left or right of the content upon the second drawing.

This fixes https://savannah.gnu.org/bugs/?50877.

An iterator should not be called "start_col", because it is only the
starting column at the very beginning.

Also, start_col (after the rename) can never be /larger/ than column.

The mbwidth() function itself checks whether UTF-8 is being used
and does the right thing.

Also, mention that help texts can now be searched through, update
a copyright notice, and update and simplify a copyright year.

And in the process transform the token DISABLE_HELP to ENABLE_HELP.

The top-left corner changing is far more conspicuous than the top right.

Allow the user to search in a help text with ^W and M-W.

Achieve this by not writing the help text directly to the screen
but first writing it to a temporary file and then opening this file
in a new buffer, and treating it specially: the normal file-reading
feedback is suppressed, the titlebar shows the headline of the text,
the cursor is hidden, and the menu is limited to just the up and down
movements and searching.

This fulfills https://savannah.gnu.org/bugs/?28994

.
Signed-off-by: Rishabh Dave <rishabhddave@gmail.com>

This fixes https://savannah.gnu.org/bugs/?50872.

The go_back_chunks() function will do this clipping.

This fixes https://savannah.gnu.org/bugs/?50866.

It takes almost no code and is a useful little improvement over Pico.

Because nothing gets reset to zero or to some initial value.

To avoid an ncurses hiccup (miscoloring) when running on musl.

This fixes https://savannah.gnu.org/bugs/?50787

.
Reported-by: Avi Halachmi <avihpit@yahoo.com>

The cursor needs to be placed in its proper spot in the edit window
/only/ when nano is about to accept input from the user and needs to
show where this input will go.

(This might cause a scrolling issue to appear, because reset_cursor()
does not just place the cursor, it also recomputes current_y, which
is used in several places to determine whether and how much to scroll.
If it so happens, we'll deal with that fallout later.)