Add search to Erlang shell's history

Search mode can be entered by pressing ctrl-r. Enter terms and press
ctrl-r again to search backwards, or ctrl-s to then search forward (if
you terminal doesn't eat up that one). Press enter to execute the line,
or use tab, arrow keys, or other control sequences (^D, ^K, etc.) to
exit search mode while remaining on the last found line. Exiting is also
possible by pressing the escape key twice.

The search mode is a simpler version of the one available in bash or
zsh shells.

This adds a few modes to the shell (search, on top of none and meta) in
group.erl for history search, and a few more in edlin.erl to change the
meaning of control sequences while searching.

2 files changed, 236 insertions, 13 deletions

diff --git a/lib/kernel/src/group.erl b/lib/kernel/src/group.erl
index 4d2e31a429..c66e823a04 100644
--- a/lib/kernel/src/group.erl
+++ b/lib/kernel/src/group.erl
@@ -515,6 +515,27 @@ get_line1({undefined,{_A,Mode,Char},Cs,Cont,Rs}, Drv, Ls0, Encoding)
 		      Drv,
 		      Ls, Encoding)
     end;
+%% ^R = backward search, ^S = forward search.
+%% Search is tricky to implement and does a lot of back-and-forth
+%% work with edlin.erl (from stdlib). Edlin takes care of writing
+%% and handling lines and escape characters to get out of search,
+%% whereas this module does the actual searching and appending to lines.
+%% Erlang's shell wasn't exactly meant to traverse the wall between
+%% line and line stack, so we at least restrict it by introducing
+%% new modes: search, search_quit, search_found. These are added to
+%% the regular ones (none, meta_left_sq_bracket) and handle special
+%% cases of history search.
+get_line1({undefined,{_A,Mode,Char},Cs,Cont,Rs}, Drv, Ls, Encoding)
+  when ((Mode =:= none) and (Char =:= $\^R)) ->
+    send_drv_reqs(Drv, Rs),
+    %% drop current line, move to search mode. We store the current
+    %% prompt ('N>') and substitute it with the search prompt.
+    send_drv_reqs(Drv, edlin:erase_line(Cont)),
+    put(search_quit_prompt, edlin:prompt(Cont)),
+    Pbs = prompt_bytes("(search)`': ", Encoding),
+    {more_chars,Ncont,Nrs} = edlin:start(Pbs, search),
+    send_drv_reqs(Drv, Nrs),
+    get_line1(edlin:edit_line1(Cs, Ncont), Drv, Ls, Encoding);
 get_line1({expand, Before, Cs0, Cont,Rs}, Drv, Ls0, Encoding) ->
     send_drv_reqs(Drv, Rs),
     ExpandFun = get(expand_fun),
@@ -535,8 +556,59 @@ get_line1({undefined,_Char,Cs,Cont,Rs}, Drv, Ls, Encoding) ->
     send_drv_reqs(Drv, Rs),
     send_drv(Drv, beep),
     get_line1(edlin:edit_line(Cs, Cont), Drv, Ls, Encoding);
+%% The search item was found and accepted (new line entered on the exact
+%% result found)
+get_line1({_What,Cont={line,_Prompt,_Chars,search_found},Rs}, Drv, Ls0, Encoding) ->
+    Line = edlin:current_line(Cont),
+    %% this may create duplicate entries.
+    Ls = save_line(new_stack(get_lines(Ls0)), Line),
+    get_line1({done, Line, "", Rs}, Drv, Ls, Encoding);
+%% The search mode has been exited, but the user wants to remain in line
+%% editing mode wherever that was, but editing the search result.
+get_line1({What,Cont={line,_Prompt,_Chars,search_quit},Rs}, Drv, Ls, Encoding) ->
+    Line = edlin:current_chars(Cont),
+    %% Load back the old prompt with the correct line number.
+    case get(search_quit_prompt) of
+	undefined -> % should not happen. Fallback.
+	    LsFallback = save_line(new_stack(get_lines(Ls)), Line),
+	    get_line1({done, "\n", Line, Rs}, Drv, LsFallback, Encoding);
+	Prompt -> % redraw the line and keep going with the same stack position
+	    NCont = {line,Prompt,{lists:reverse(Line),[]},none},
+	    send_drv_reqs(Drv, Rs),
+	    send_drv_reqs(Drv, edlin:erase_line(Cont)),
+	    send_drv_reqs(Drv, edlin:redraw_line(NCont)),
+	    get_line1({What, NCont ,[]}, Drv, pad_stack(Ls), Encoding)
+    end;
+%% Search mode is entered.
+get_line1({What,{line,Prompt,{RevCmd0,_Aft},search},Rs},
+       Drv, Ls0, Encoding) ->
+    send_drv_reqs(Drv, Rs),
+    %% Figure out search direction. ^S and ^R are returned through edlin
+    %% whenever we received a search while being already in search mode.
+    {Search, Ls1, RevCmd} = case RevCmd0 of
+	[$\^S|RevCmd1] ->
+	    {fun search_down_stack/2, Ls0, RevCmd1};
+	[$\^R|RevCmd1] ->
+	    {fun search_up_stack/2, Ls0, RevCmd1};
+	_ -> % new search, rewind stack for a proper search.
+	    {fun search_up_stack/2, new_stack(get_lines(Ls0)), RevCmd0}
+    end,
+    Cmd = lists:reverse(RevCmd),
+    {Ls, NewStack} = case Search(Ls1, Cmd) of
+	{none, Ls2} ->
+	    send_drv(Drv, beep),
+	    {Ls2, {RevCmd, "': "}};
+	{Line, Ls2} -> % found. Complete the output edlin couldn't have done.
+	    send_drv_reqs(Drv, [{put_chars, Encoding, Line}]),
+	    {Ls2, {RevCmd, "': "++Line}}
+    end,
+    Cont = {line,Prompt,NewStack,search},
+    more_data(What, Cont, Drv, Ls, Encoding);
 get_line1({What,Cont0,Rs}, Drv, Ls, Encoding) ->
     send_drv_reqs(Drv, Rs),
+    more_data(What, Cont0, Drv, Ls, Encoding).
+
+more_data(What, Cont0, Drv, Ls, Encoding) ->
     receive
 	{Drv,{data,Cs}} ->
 	    get_line1(edlin:edit_line(Cs, Cont0), Drv, Ls, Encoding);
@@ -557,7 +629,6 @@ get_line1({What,Cont0,Rs}, Drv, Ls, Encoding) ->
 	    get_line1(edlin:edit_line([], Cont0), Drv, Ls, Encoding)
     end.
 
-
 get_line_echo_off(Chars, Pbs, Drv) ->
     send_drv_reqs(Drv, [{put_chars, unicode,Pbs}]),
     get_line_echo_off1(edit_line(Chars,[]), Drv).
@@ -632,12 +703,46 @@ save_line({stack, U, {}, []}, Line) ->
 save_line({stack, U, _L, D}, Line) ->
     {stack, U, Line, D}.
 
-get_lines({stack, U, {}, []}) ->
+get_lines(Ls) -> get_all_lines(Ls).
+%get_lines({stack, U, {}, []}) ->
+%    U;
+%get_lines({stack, U, {}, D}) ->
+%    tl(lists:reverse(D, U));
+%get_lines({stack, U, L, D}) ->
+%    get_lines({stack, U, {}, [L|D]}).
+
+%% There's a funny behaviour whenever the line stack doesn't have a "\n"
+%% at its end -- get_lines() seemed to work on the assumption it *will* be
+%% there, but the manipulations done with search history do not require it.
+%%
+%% It is an assumption because the function was built with either the full
+%% stack being on the 'Up' side (we're on the new line) where it isn't
+%% stripped. The only other case when it isn't on the 'Up' side is when
+%% someone has used the up/down arrows (or ^P and ^N) to navigate lines,
+%% in which case, a line with only a \n is stored at the end of the stack
+%% (the \n is returned by edlin:current_line/1).
+%%
+%% get_all_lines works the same as get_lines, but only strips the trailing
+%% character if it's a linebreak. Otherwise it's kept the same. This is
+%% because traversing the stack due to search history will *not* insert
+%% said empty line in the stack at the same time as other commands do,
+%% and thus it should not always be stripped unless we know a new line
+%% is the last entry.
+get_all_lines({stack, U, {}, []}) ->
     U;
-get_lines({stack, U, {}, D}) ->
-    tl(lists:reverse(D, U));
-get_lines({stack, U, L, D}) ->
-    get_lines({stack, U, {}, [L|D]}).
+get_all_lines({stack, U, {}, D}) ->
+    case lists:reverse(D, U) of
+	["\n"|Lines] -> Lines;
+	Lines -> Lines
+    end;
+get_all_lines({stack, U, L, D}) ->
+    get_all_lines({stack, U, {}, [L|D]}).
+
+%% For the same reason as above, though, we need to expand the stack
+%% in some cases to make sure we play nice with up/down arrows. We need
+%% to insert newlines, but not always.
+pad_stack({stack, U, L, D}) ->
+    {stack, U, L, D++["\n"]}.
 
 save_line_buffer("\n", Lines) ->
     save_line_buffer(Lines);
@@ -649,6 +754,27 @@ save_line_buffer(Line, Lines) ->
 save_line_buffer(Lines) ->
     put(line_buffer, Lines).
 
+search_up_stack(Stack, Substr) ->
+    case up_stack(Stack) of
+	{none,NewStack} -> {none,NewStack};
+	{L, NewStack} ->
+	    case string:str(L, Substr) of
+		0 -> search_up_stack(NewStack, Substr);
+		_ -> {string:strip(L,right,$\n), NewStack}
+	    end
+    end.
+
+search_down_stack(Stack, Substr) ->
+    case down_stack(Stack) of
+	{none,NewStack} -> {none,NewStack};
+	{L, NewStack} ->
+	    case string:str(L, Substr) of
+		0 -> search_down_stack(NewStack, Substr);
+		_ -> {string:strip(L,right,$\n), NewStack}
+	    end
+    end.
+
+
 %% This is get_line without line editing (except for backspace) and
 %% without echo.
 get_password_line(Chars, Drv) ->
@@ -687,7 +813,7 @@ edit_password([$\177|Cs],[_|Chars]) ->%% is backspace enough?
 edit_password([Char|Cs],Chars) ->
     edit_password(Cs,[Char|Chars]).
 
-%% prompt_bytes(Prompt)
+%% prompt_bytes(Prompt, Encoding)
 %%  Return a flat list of characters for the Prompt.
 prompt_bytes(Prompt, Encoding) ->
     lists:flatten(io_lib:format_prompt(Prompt, Encoding)).
diff --git a/lib/stdlib/src/edlin.erl b/lib/stdlib/src/edlin.erl
index 1164ee49eb..3192879f09 100644
--- a/lib/stdlib/src/edlin.erl
+++ b/lib/stdlib/src/edlin.erl
@@ -22,10 +22,10 @@
 %% A simple Emacs-like line editor.
 %% About Latin-1 characters: see the beginning of erl_scan.erl.
 
--export([init/0,start/1,edit_line/2,prefix_arg/1]).
+-export([init/0,start/1,start/2,edit_line/2,prefix_arg/1]).
 -export([erase_line/1,erase_inp/1,redraw_line/1]).
 -export([length_before/1,length_after/1,prompt/1]).
--export([current_line/1]).
+-export([current_line/1, current_chars/1]).
 %%-export([expand/1]).
 
 -export([edit_line1/2]).
@@ -54,7 +54,12 @@ init() ->
 %%	{undefined,Char,Rest,Cont,Requests}
 
 start(Pbs) ->
-    {more_chars,{line,Pbs,{[],[]},none},[{put_chars,unicode,Pbs}]}.
+    start(Pbs, none).
+
+%% Only two modes used: 'none' and 'search'. Other modes can be
+%% handled inline through specific character handling.
+start(Pbs, Mode) ->
+    {more_chars,{line,Pbs,{[],[]},Mode},[{put_chars,unicode,Pbs}]}.
 
 edit_line(Cs, {line,P,L,{blink,N}}) ->
     edit(Cs, P, L, none, [{move_rel,N}]);
@@ -76,6 +81,10 @@ edit([C|Cs], P, {Bef,Aft}, Prefix, Rs0) ->
 	    edit(Cs, P, {Bef,Aft}, meta, Rs0);
 	meta_left_sq_bracket ->
 	    edit(Cs, P, {Bef,Aft}, meta_left_sq_bracket, Rs0);
+	search_meta ->
+	    edit(Cs, P, {Bef,Aft}, search_meta, Rs0);
+	search_meta_left_sq_bracket ->
+	    edit(Cs, P, {Bef,Aft}, search_meta_left_sq_bracket, Rs0);
 	ctlx ->
 	    edit(Cs, P, {Bef,Aft}, ctlx, Rs0);
 	new_line ->
@@ -115,6 +124,8 @@ edit([C|Cs], P, {Bef,Aft}, Prefix, Rs0) ->
 	    case do_op(Op, Bef, Aft, Rs0) of
 		{blink,N,Line,Rs} ->
 		    edit(Cs, P, Line, {blink,N}, Rs);
+		{Line, Rs, Mode} -> % allow custom modes from do_op
+		    edit(Cs, P, Line, Mode, Rs);
 		{Line,Rs} ->
 		    edit(Cs, P, Line, none, Rs)
 	    end
@@ -168,9 +179,15 @@ key_map($\^], none) -> auto_blink;
 key_map($\^X, none) -> ctlx;
 key_map($\^Y, none) -> yank;
 key_map($\e, none) -> meta;
-key_map($), Prefix) when Prefix =/= meta -> {blink,$),$(};
-key_map($}, Prefix) when Prefix =/= meta -> {blink,$},${};
-key_map($], Prefix) when Prefix =/= meta -> {blink,$],$[};
+key_map($), Prefix) when Prefix =/= meta,
+                         Prefix =/= search,
+                         Prefix =/= search_meta -> {blink,$),$(};
+key_map($}, Prefix) when Prefix =/= meta,
+                         Prefix =/= search,
+                         Prefix =/= search_meta -> {blink,$},${};
+key_map($], Prefix) when Prefix =/= meta,
+                         Prefix =/= search,
+                         Prefix =/= search_meta -> {blink,$],$[};
 key_map($B, meta) -> backward_word;
 key_map($D, meta) -> kill_word;
 key_map($F, meta) -> forward_word;
@@ -188,6 +205,32 @@ key_map($D, meta_left_sq_bracket) -> backward_char;
 key_map($C, meta_left_sq_bracket) -> forward_char;
 key_map(C, none) when C >= $\s ->
     {insert,C};
+%% for search, we need smarter line handling and so
+%% we cheat a bit on the dispatching, and allow to
+%% return a mode.
+key_map($\^H, search) -> {search, backward_delete_char};
+key_map($\177, search) -> {search, backward_delete_char};
+key_map($\^R, search) -> {search, skip_up};
+key_map($\^S, search) -> {search, skip_down};
+key_map($\n, search) -> {search, search_found};
+key_map($\r, search) -> {search, search_found};
+key_map($\^A, search) -> {search, search_quit};
+key_map($\^B, search) -> {search, search_quit};
+key_map($\^D, search) -> {search, search_quit};
+key_map($\^E, search) -> {search, search_quit};
+key_map($\^F, search) -> {search, search_quit};
+key_map($\t,  search) -> {search, search_quit};
+key_map($\^L, search) -> {search, search_quit};
+key_map($\^T, search) -> {search, search_quit};
+key_map($\^U, search) -> {search, search_quit};
+key_map($\^], search) -> {search, search_quit};
+key_map($\^X, search) -> {search, search_quit};
+key_map($\^Y, search) -> {search, search_quit};
+key_map($\e,  search) -> search_meta;
+key_map($[,  search_meta) -> search_meta_left_sq_bracket;
+key_map(_, search_meta) -> {search, search_quit};
+key_map(_C, search_meta_left_sq_bracket) -> {search, search_quit};
+key_map(C, search) -> {insert_search,C};
 key_map(C, _) -> {undefined,C}.
 
 %% do_op(Action, Before, After, Requests)
@@ -196,6 +239,57 @@ do_op({insert,C}, Bef, [], Rs) ->
     {{[C|Bef],[]},[{put_chars, unicode,[C]}|Rs]};
 do_op({insert,C}, Bef, Aft, Rs) ->
     {{[C|Bef],Aft},[{insert_chars, unicode, [C]}|Rs]};
+%% Search mode prompt always looks like (search)`$TERMS': $RESULT.
+%% the {insert_search, _} handlings allow to share this implementation
+%% correctly with group.erl. This module provides $TERMS, and group.erl
+%% is in charge of providing $RESULT.
+%% This require a bit of trickery. Because search disables moving around
+%% on the line (left/right arrow keys and other shortcuts that just exit
+%% search mode), we can use the Bef and Aft variables to hold each
+%% part of the line. Bef takes charge of "(search)`$TERMS" and Aft
+%% takes charge of "': $RESULT".
+do_op({insert_search, C}, Bef, [], Rs) ->
+    Aft="': ",
+    {{[C|Bef],Aft},
+     [{insert_chars, unicode, [C]++Aft}, {delete_chars,-3} | Rs],
+     search};
+do_op({insert_search, C}, Bef, Aft, Rs) ->
+    Offset= length(Aft),
+    NAft = "': ",
+    {{[C|Bef],NAft},
+     [{insert_chars, unicode, [C]++NAft}, {delete_chars,-Offset} | Rs],
+     search};
+do_op({search, backward_delete_char}, [_|Bef], Aft, Rs) ->
+    Offset= length(Aft)+1,
+    NAft = "': ",
+    {{Bef,NAft},
+     [{insert_chars, unicode, NAft}, {delete_chars,-Offset}|Rs],
+     search};
+do_op({search, backward_delete_char}, [], _Aft, Rs) ->
+    Aft="': ",
+    {{[],Aft}, Rs, search};
+do_op({search, skip_up}, Bef, Aft, Rs) ->
+    Offset= length(Aft),
+    NAft = "': ",
+    {{[$\^R|Bef],NAft}, % we insert ^R as a flag to whoever called us
+     [{insert_chars, unicode, NAft}, {delete_chars,-Offset}|Rs],
+     search};
+do_op({search, skip_down}, Bef, Aft, Rs) ->
+    Offset= length(Aft),
+    NAft = "': ",
+    {{[$\^S|Bef],NAft}, % we insert ^S as a flag to whoever called us
+     [{insert_chars, unicode, NAft}, {delete_chars,-Offset}|Rs],
+     search};
+do_op({search, search_found}, _Bef, Aft, Rs) ->
+    "': "++NAft = Aft,
+    {{[],NAft},
+     [{put_chars, unicode, "\n"}, {move_rel,-length(Aft)} | Rs],
+     search_found};
+do_op({search, search_quit}, _Bef, Aft, Rs) ->
+    "': "++NAft = Aft,
+    {{[],NAft},
+     [{put_chars, unicode, "\n"}, {move_rel,-length(Aft)} | Rs],
+     search_quit};
 %% do blink after $$
 do_op({blink,C,M}, Bef=[$$,$$|_], Aft, Rs) ->
     N = over_paren(Bef, C, M),
@@ -453,6 +547,9 @@ prompt({line,Pbs,_,_}) ->
 current_line({line,_,{Bef, Aft},_}) ->
     reverse(Bef, Aft ++ "\n").
 
+current_chars({line,_,{Bef,Aft},_}) ->
+    reverse(Bef, Aft).
+
 %% %% expand(CurrentBefore) ->
 %% %%	{yes,Expansion} | no
 %% %%  Try to expand the word before as either a module name or a function