feat: layout anchor (#1582)

* feat: add `anchor` option to some `layout_strategies`

* tests: improve tests for `resolve_height/width`

lua/telescope/config/resolve.lua

@@ -213,6 +213,35 @@ resolver.resolve_width = function(val)
   error("invalid configuration option for width:" .. tostring(val))
 end
 
+--- Calculates the adjustment required to move the picker from the middle of the screen to
+--- an edge or corner. <br>
+--- The `anchor` can be any of the following strings:
+---   - "", "CENTER", "NW", "N", "NE", "E", "SE", "S", "SW", "W"
+--- The anchors have the following meanings:
+---   - "" or "CENTER":<br>
+---     the picker will remain in the middle of the screen.
+---   - Compass directions:<br>
+---     the picker will move to the corresponding edge/corner
+---     e.g. "NW" -> "top left corner", "E" -> "right edge", "S" -> "bottom edge"
+resolver.resolve_anchor_pos = function(anchor, p_width, p_height, max_columns, max_lines)
+  anchor = anchor:upper()
+  local pos = { 0, 0 }
+  if anchor == "CENTER" then
+    return pos
+  end
+  if anchor:find "W" then
+    pos[1] = math.ceil((p_width - max_columns) / 2) + 1
+  elseif anchor:find "E" then
+    pos[1] = math.ceil((max_columns - p_width) / 2) - 1
+  end
+  if anchor:find "N" then
+    pos[2] = math.ceil((p_height - max_lines) / 2) + 1
+  elseif anchor:find "S" then
+    pos[2] = math.ceil((max_lines - p_height) / 2) - 1
+  end
+  return pos
+end
+
 -- Win option always returns a table with preview, results, and prompt.
 -- It handles many different ways. Some examples are as follows:
 --