feat: add match_listing / truncate setting

For: #429

Some disgusting arithmetic in here, so hopefully it's correct.

Note that this setting takes string values:

- 'beginning'
- 'middle' (the default)
- 'end' (the old behavior prior to this commit)

But also booleans:

- true (same as 'middle')
- false (same as 'end')

And for foolproof-ness, stringy booleans:

- 'true'
- 'false'

Note that 'middle' is a reasonable default because that's what the old
Ruby implementation did (and it wasn't even configurable):

- https://github.com/wincent/command-t/blob/3e937f91260acca0061d884d0ff3c9a521c1fde9/ruby/command-t/lib/command-t/match_window.rb#L478-L487

Also note that when 'end', we don't show an actual ellipsis; we just cut
off the text at the right edge.

Author: wincent

doc/command-t.txt

@@ -421,6 +421,7 @@ are documented and they could change without notice at any time; for example:
         -- 'double', 'none', 'rounded', 'shadow', 'single', 'solid', or a
         -- list of strings.
         border = { '', '', '', '│', '┘', '─', '└', '│' },
+        truncate = 'middle', -- 'beginning', 'end', true, false.
       },
       never_show_dot_files = false,
       order = 'forward', -- 'forward' or 'reverse'.
@@ -610,6 +611,20 @@ Possible vaules are:
   (above), but instead of starting from the file currently being edited, start
   from Neovim's present working directory.
 
+                                              *command-t-truncate*
+                                              string (default: 'middle')
+
+Controls how entries that are too wide to fit inside the match listing are
+truncated. Possible values are:
+
+- `'beginning'`: entries are truncated at the beginning (ie. "...bazqux").
+- `'middle'`: entries are truncated in the middle (ie. "foo...qux").
+- `'end'`: entries are truncated at the end (ie. "foobarbaz").
+- `true`: same as `'middle'`.
+- `false`: same as `'end'`).
+
+Note that when set to `'end'` (or `false`), no ellipsis is shown.
+
 
 MAPPINGS                                        *command-t-mappings*
 
@@ -822,6 +837,8 @@ main (not yet released) ~
 - feat: add `match_listing` / `border` and `prompt` / `border` settings.
 - feat: add `traverse` and `root_markers` settings
   (https://github.com/wincent/command-t/issues/416).
+- feat: add `match_listing` / `truncate` setting
+  (https://github.com/wincent/command-t/discussions/429).
 
 6.0.0-b.1 (16 December 2022) ~
 

lua/wincent/commandt/init.lua

@@ -133,6 +133,18 @@ local options_spec = {
             },
           },
         },
+        truncate = {
+          kind = {
+            one_of = {
+              'beginning',
+              'middle',
+              'end',
+              'true',
+              'false',
+              { kind = 'boolean' },
+            },
+          },
+        },
       },
     },
     never_show_dot_files = { kind = 'boolean' },
@@ -461,6 +473,7 @@ local default_options = {
   margin = 10,
   match_listing = {
     border = { '', '', '', '│', '┘', '─', '└', '│' }, -- 'double', 'none', 'rounded', 'shadow', 'single', 'solid', or a list of strings.
+    truncate = 'middle',
   },
   never_show_dot_files = false,
   order = 'forward', -- 'forward', 'reverse'.

lua/wincent/commandt/private/match_listing.lua

@@ -22,6 +22,7 @@ function MatchListing.new(options)
     margin = 0,
     position = 'bottom',
     selection_highlight = 'PmenuSel',
+    truncate = 'middle',
   }, options or {})
   -- TODO: validate options
   local m = {
@@ -33,6 +34,7 @@ function MatchListing.new(options)
     _results = nil,
     _selected = nil,
     _selection_highlight = options.selection_highlight,
+    _truncate = options.truncate,
     _window = nil,
   }
   setmetatable(m, mt)
@@ -45,7 +47,7 @@ function MatchListing:close()
   end
 end
 
-local format_line = function(line, width, selected)
+local format_line = function(line, width, selected, truncate)
   local prefix = selected and '> ' or '  '
 
   -- Sanitize some control characters, plus blackslashes.
@@ -58,6 +60,21 @@ local format_line = function(line, width, selected)
     :gsub('\t', '\\t')
     :gsub('\v', '\\v')
 
+  if #line + #prefix < width then
+    -- Line fits without trimming.
+  elseif #line < 5 then
+    -- Line is so short that adding an ellipsis is not practical.
+  elseif truncate == true or truncate == 'true' or truncate == 'middle' then
+    local half = math.floor((width - 2) / 2)
+    local left = line:sub(1, half - 2 + width % 2)
+    local right = line:sub(2 - half)
+    line = left .. '...' .. right
+  elseif truncate == 'beginning' then
+    line = '...' .. line:sub(-width + #prefix + 3)
+  elseif truncate == false or truncate == 'false' or truncate == 'end' then
+    -- Fall through; truncation will happen before the final `return`.
+  end
+
   -- Right pad so that selection highlighting is shown across full width.
   if width < 102 and #line > 99 then
     -- No padding needed.
@@ -73,7 +90,7 @@ local format_line = function(line, width, selected)
     end
   end
 
-  -- Trim right to make sure we never wrap.
+  -- Trim to make sure we never wrap.
   return line:sub(1, width)
 end
 
@@ -84,12 +101,12 @@ function MatchListing:select(selected)
   if self._window then
     local width = self._window:width() or vim.o.columns -- BUG: width may be cached/stale
 
-    local previous_selection = format_line(self._results[self._selected], width, false)
+    local previous_selection = format_line(self._results[self._selected], width, false, self._truncate)
     self._window:replace_line(previous_selection, self._selected)
     self._window:unhighlight_line(self._selected)
 
     self._selected = selected
-    local new_selection = format_line(self._results[self._selected], width, true)
+    local new_selection = format_line(self._results[self._selected], width, true, self._truncate)
     self._window:replace_line(new_selection, self._selected)
     self._window:highlight_line(self._selected)
   end
@@ -150,7 +167,7 @@ function MatchListing:update(results, options)
     self._lines = {}
     for i, result in ipairs(results) do
       local selected = i == self._selected
-      local line = format_line(result, width, selected)
+      local line = format_line(result, width, selected, self._truncate)
       table.insert(self._lines, line)
     end
     self._window:unhighlight()

lua/wincent/commandt/private/ui.lua

@@ -91,6 +91,7 @@ ui.show = function(finder, options)
     margin = options.margin,
     position = options.position,
     selection_highlight = options.selection_highlight,
+    truncate = options.match_listing.truncate,
   })
   match_listing:show()