REPL: tab/backspace aligns to 4 (#22939)

* REPL: tab/backspace aligns to 4

* when pressing tab, compute the number of spaces to insert
  so that the cursor is aligned to a multiple of 4 chars
* when pressing backspace, delete up to 4 spaces so that
  the cursor is aligned to a multiple of 4 chars

* multispaces defaults to false, and de-activate in search-mode

* tab: jump to end of line; backspace: try to keep right side aligned

* cosmetic changes

base/repl/LineEdit.jl

@@ -478,22 +478,49 @@ function edit_insert(buf::IOBuffer, c)
     end
 end
 
-function edit_backspace(s::PromptState)
-    if edit_backspace(s.input_buffer)
-        refresh_line(s)
-    else
-        beep(terminal(s))
-    end
+# align: delete up to 4 spaces to align to a multiple of 4 chars
+# adjust: also delete spaces on the right of the cursor to try to keep aligned what is
+# on the right
+edit_backspace(s::PromptState, align::Bool=false, adjust=align) =
+    edit_backspace(s.input_buffer, align) ? refresh_line(s) : beep(terminal(s))
+
+const _newline =  UInt8('\n')
+const _space = UInt8(' ')
+
+_notspace(c) = c != _space
+
+beginofline(buf, pos=position(buf)) = findprev(buf.data, _newline, pos)
+
+function endofline(buf, pos=position(buf))
+    eol = findnext(buf.data[pos+1:buf.size], _newline, 1)
+    eol == 0 ? buf.size : pos + eol - 1
 end
-function edit_backspace(buf::IOBuffer)
-    if position(buf) > 0
-        oldpos = position(buf)
-        char_move_left(buf)
-        splice_buffer!(buf, position(buf):oldpos-1)
-        return true
-    else
-        return false
+
+function edit_backspace(buf::IOBuffer, align::Bool=false, adjust::Bool=align)
+    !align && adjust &&
+        throw(DomainError((align, adjust),
+                          "if `adjust` is `true`, `align` must be `true`"))
+    oldpos = position(buf)
+    oldpos == 0 && return false
+    c = char_move_left(buf)
+    newpos = position(buf)
+    if align && c == ' ' # maybe delete multiple spaces
+        beg = beginofline(buf, newpos)
+        align = strwidth(String(buf.data[1+beg:newpos])) % 4
+        nonspace = findprev(_notspace, buf.data, newpos)
+        if newpos - align >= nonspace
+            newpos -= align
+            seek(buf, newpos)
+            if adjust
+                spaces = findnext(_notspace, buf.data[newpos+2:buf.size], 1)
+                oldpos = spaces == 0 ? buf.size :
+                    buf.data[newpos+1+spaces] == _newline ? newpos+spaces :
+                    newpos + min(spaces, 4)
+            end
+        end
     end
+    splice_buffer!(buf, newpos:oldpos-1)
+    return true
 end
 
 edit_delete(s) = edit_delete(buffer(s)) ? refresh_line(s) : beep(terminal(s))
@@ -1337,30 +1364,52 @@ function bracketed_paste(s)
     return replace(input, '\t', " "^tabwidth)
 end
 
+function tab_should_complete(s)
+    # Yes, we are ignoring the possiblity
+    # the we could be in the middle of a multi-byte
+    # sequence, here but that's ok, since any
+    # whitespace we're interested in is only one byte
+    buf = buffer(s)
+    pos = position(buf)
+    pos == 0 && return true
+    c = buf.data[pos]
+    c != _newline && c != UInt8('\t') &&
+        # hack to allow path completion in cmds
+        # after a space, e.g., `cd <tab>`, while still
+        # allowing multiple indent levels
+        (c != _space || pos <= 3 || buf.data[pos-1] != _space)
+end
+
+# jump_spaces: if cursor is on a ' ', move it to the first non-' ' char on the right
+# if `delete_trailing`, ignore trailing ' ' by deleting them
+function edit_tab(s, jump_spaces=false, delete_trailing=jump_spaces)
+    tab_should_complete(s) ?
+        complete_line(s) :
+        edit_tab(buffer(s), jump_spaces, delete_trailing)
+    refresh_line(s)
+end
+
+function edit_tab(buf::IOBuffer, jump_spaces=false, delete_trailing=jump_spaces)
+    i = position(buf)
+    if jump_spaces && i < buf.size && buf.data[i+1] == _space
+        spaces = findnext(_notspace, buf.data[i+1:buf.size], 1)
+        if delete_trailing && (spaces == 0 || buf.data[i+spaces] == _newline)
+            splice_buffer!(buf, i:(spaces == 0 ? buf.size-1 : i+spaces-2))
+        else
+            jump = spaces == 0 ? buf.size : i+spaces-1
+            return seek(buf, jump)
+        end
+    end
+    # align to multiples of 4:
+    align = 4 - strwidth(String(buf.data[1+beginofline(buf, i):i])) % 4
+    return edit_insert(buf, ' '^align)
+end
+
+
 const default_keymap =
 AnyDict(
     # Tab
-    '\t' => (s,o...)->begin
-        buf = buffer(s)
-        # Yes, we are ignoring the possiblity
-        # the we could be in the middle of a multi-byte
-        # sequence, here but that's ok, since any
-        # whitespace we're interested in is only one byte
-        i = position(buf)
-        if i != 0
-            c = buf.data[i]
-            if c == UInt8('\n') || c == UInt8('\t') ||
-               # hack to allow path completion in cmds
-               # after a space, e.g., `cd <tab>`, while still
-               # allowing multiple indent levels
-               (c == UInt8(' ') && i > 3 && buf.data[i-1] == UInt8(' '))
-                edit_insert(s, " "^4)
-                return
-            end
-        end
-        complete_line(s)
-        refresh_line(s)
-    end,
+    '\t' => (s,o...)->edit_tab(s, true),
     # Enter
     '\r' => (s,o...)->begin
         if on_enter(s) || (eof(buffer(s)) && s.key_repeats > 1)
@@ -1372,7 +1421,7 @@ AnyDict(
     end,
     '\n' => KeyAlias('\r'),
     # Backspace/^H
-    '\b' => (s,o...)->edit_backspace(s),
+    '\b' => (s,o...)->edit_backspace(s, true),
     127 => KeyAlias('\b'),
     # Meta Backspace
     "\e\b" => (s,o...)->edit_delete_prev_word(s),

test/lineedit.jl

@@ -427,3 +427,83 @@ end
         "\r\e[2C    julia = :fun\n" *
         "\r\e[2Cend\r\e[5C"
 end
+
+@testset "tab/backspace alignment feature" begin
+    term = TestHelpers.FakeTerminal(IOBuffer(), IOBuffer(), IOBuffer())
+    s = LineEdit.init_state(term, ModalInterface([Prompt("test> ")]))
+    function bufferdata(s)
+        buf = LineEdit.buffer(s)
+        String(buf.data[1:buf.size])
+    end
+    move_left(s, n) = for x = 1:n
+        LineEdit.edit_move_left(s)
+    end
+
+    bufpos(s::Base.LineEdit.MIState) = position(LineEdit.buffer(s))
+
+    LineEdit.edit_insert(s, "for x=1:10\n")
+    LineEdit.edit_tab(s)
+    @test bufferdata(s) == "for x=1:10\n    "
+    LineEdit.edit_backspace(s, true, false)
+    @test bufferdata(s) == "for x=1:10\n"
+    LineEdit.edit_insert(s, "  ")
+    @test bufpos(s) == 13
+    LineEdit.edit_tab(s)
+    @test bufferdata(s) == "for x=1:10\n    "
+    LineEdit.edit_insert(s, "  ")
+    LineEdit.edit_backspace(s, true, false)
+    @test bufferdata(s) == "for x=1:10\n    "
+    LineEdit.edit_insert(s, "éé=3   ")
+    LineEdit.edit_tab(s)
+    @test bufferdata(s) == "for x=1:10\n    éé=3    "
+    LineEdit.edit_backspace(s, true, false)
+    @test bufferdata(s) == "for x=1:10\n    éé=3"
+    LineEdit.edit_insert(s, "\n    1∉x  ")
+    LineEdit.edit_tab(s)
+    @test bufferdata(s) == "for x=1:10\n    éé=3\n    1∉x     "
+    LineEdit.edit_backspace(s, false, false)
+    @test bufferdata(s) == "for x=1:10\n    éé=3\n    1∉x    "
+    LineEdit.edit_backspace(s, true, false)
+    @test bufferdata(s) == "for x=1:10\n    éé=3\n    1∉x "
+    LineEdit.edit_move_word_left(s)
+    LineEdit.edit_tab(s)
+    @test bufferdata(s) == "for x=1:10\n    éé=3\n        1∉x "
+    LineEdit.move_line_start(s)
+    @test bufpos(s) == 22
+    LineEdit.edit_tab(s, true)
+    @test bufferdata(s) == "for x=1:10\n    éé=3\n        1∉x "
+    @test bufpos(s) == 30
+    LineEdit.edit_move_left(s)
+    @test bufpos(s) == 29
+    LineEdit.edit_backspace(s, true, true)
+    @test bufferdata(s) == "for x=1:10\n    éé=3\n    1∉x "
+    @test bufpos(s) == 26
+    LineEdit.edit_tab(s, false) # same as edit_tab(s, true) here
+    @test bufpos(s) == 30
+    move_left(s, 6)
+    @test bufpos(s) == 24
+    LineEdit.edit_backspace(s, true, true)
+    @test bufferdata(s) == "for x=1:10\n    éé=3\n    1∉x "
+    @test bufpos(s) == 22
+    LineEdit.edit_kill_line(s)
+    LineEdit.edit_insert(s, ' '^10)
+    move_left(s, 7)
+    @test bufferdata(s) == "for x=1:10\n    éé=3\n          "
+    @test bufpos(s) == 25
+    LineEdit.edit_tab(s, true, false)
+    @test bufpos(s) == 32
+    move_left(s, 7)
+    LineEdit.edit_tab(s, true, true)
+    @test bufpos(s) == 26
+    @test bufferdata(s) == "for x=1:10\n    éé=3\n    "
+    # test again the same, when there is a next line
+    LineEdit.edit_insert(s, "      \nend")
+    move_left(s, 11)
+    @test bufpos(s) == 25
+    LineEdit.edit_tab(s, true, false)
+    @test bufpos(s) == 32
+    move_left(s, 7)
+    LineEdit.edit_tab(s, true, true)
+    @test bufpos(s) == 26
+    @test bufferdata(s) == "for x=1:10\n    éé=3\n    \nend"
+end