feat: layout `anchor` (#1582)

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

* tests: improve tests for `resolve_height/width`

2 files changed, 58 insertions, 3 deletions

diff --git a/lua/telescope/config/resolve.lua b/lua/telescope/config/resolve.lua
index 9875565..3b47025 100644
--- a/lua/telescope/config/resolve.lua
+++ b/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:
 --
diff --git a/lua/telescope/pickers/layout_strategies.lua b/lua/telescope/pickers/layout_strategies.lua
index 9b1b2cd..7159797 100644
--- a/lua/telescope/pickers/layout_strategies.lua
+++ b/lua/telescope/pickers/layout_strategies.lua
@@ -107,6 +107,13 @@ local get_valid_configuration_keys = function(strategy_config)
   return valid_configuration_keys
 end
 
+local adjust_pos = function(pos, ...)
+  for _, opts in ipairs { ... } do
+    opts.col = opts.col and opts.col + pos[1]
+    opts.line = opts.line and opts.line + pos[2]
+  end
+end
+
 --@param strategy_name string: the name of the layout_strategy we are validating for
 --@param configuration table: table with keys for each option available
 --@param values table: table containing all of the non-default options we want to set
@@ -187,6 +194,7 @@ local shared_options = {
   mirror = "Flip the location of the results/prompt and preview windows",
   scroll_speed = "The number of lines to scroll through the previewer",
   prompt_position = { "Where to place prompt window.", "Available Values: 'bottom', 'top'" },
+  anchor = { "Which edge/corner to pin the picker to", "See |resolver.resolve_anchor_pos()|" },
 }
 
 -- Used for generating vim help documentation.
@@ -368,6 +376,9 @@ layout_strategies.horizontal = make_documented_layout(
       error(string.format("Unknown prompt_position: %s\n%s", self.window.prompt_position, vim.inspect(layout_config)))
     end
 
+    local anchor_pos = resolve.resolve_anchor_pos(layout_config.anchor or "", width, height, max_columns, max_lines)
+    adjust_pos(anchor_pos, prompt, results, preview)
+
     if tbln then
       prompt.line = prompt.line + 1
       results.line = results.line + 1
@@ -388,6 +399,8 @@ layout_strategies.horizontal = make_documented_layout(
 --- Particularly useful for creating dropdown menus
 --- (see |telescope.themes| and |themes.get_dropdown()|`).
 ---
+--- Note that the `anchor` option can only pin this layout to the left or right edges.
+---
 --- <pre>
 --- ┌──────────────────────────────────────────────────┐
 --- │    ┌────────────────────────────────────────┐    │
@@ -475,7 +488,12 @@ layout_strategies.center = make_documented_layout(
       preview.height = 0
     end
 
-    results.col, preview.col, prompt.col = 0, 0, 0 -- all centered
+    local width_padding = math.floor((max_columns - width) / 2) + bs + 1
+    results.col, preview.col, prompt.col = width_padding, width_padding, width_padding
+
+    local anchor_pos = resolve.resolve_anchor_pos(layout_config.anchor or "", width, height, max_columns, max_lines)
+    anchor_pos[2] = 0 -- only use horizontal anchoring
+    adjust_pos(anchor_pos, prompt, results, preview)
 
     if tbln then
       prompt.line = prompt.line + 1
@@ -514,7 +532,11 @@ layout_strategies.center = make_documented_layout(
 --- </pre>
 layout_strategies.cursor = make_documented_layout(
   "cursor",
-  vim.tbl_extend("error", shared_options, {
+  vim.tbl_extend("error", {
+    width = shared_options.width,
+    height = shared_options.height,
+    scroll_speed = shared_options.scroll_speed,
+  }, {
     preview_width = { "Change the width of Telescope's preview window", "See |resolver.resolve_width()|" },
     preview_cutoff = "When columns are less than this value, the preview will be disabled",
   }),
@@ -661,7 +683,8 @@ layout_strategies.vertical = make_documented_layout(
     prompt.height = 1
     results.height = height - preview.height - prompt.height - h_space
 
-    results.col, preview.col, prompt.col = 0, 0, 0 -- all centered
+    local width_padding = math.floor((max_columns - width) / 2) + bs + 1
+    results.col, preview.col, prompt.col = width_padding, width_padding, width_padding
 
     local height_padding = math.floor((max_lines - height) / 2)
     if not layout_config.mirror then
@@ -689,6 +712,9 @@ layout_strategies.vertical = make_documented_layout(
       end
     end
 
+    local anchor_pos = resolve.resolve_anchor_pos(layout_config.anchor or "", width, height, max_columns, max_lines)
+    adjust_pos(anchor_pos, prompt, results, preview)
+
     if tbln then
       prompt.line = prompt.line + 1
       results.line = results.line + 1