fix(lsp): Convert LSP positions to each client's offset encoding

lua/peekstack/core/location.lua

@@ -158,7 +158,9 @@ local function from_lsp_location(loc, provider)
     return nil
   end
   local uri = loc.uri or loc.targetUri
-  local range = loc.range or loc.targetRange
+  -- A LocationLink's targetRange spans the whole symbol (e.g. a function body);
+  -- targetSelectionRange is the name to land on and to compare against the cursor.
+  local range = loc.range or loc.targetSelectionRange or loc.targetRange
   if not uri or not range then
     return nil
   end
@@ -168,7 +170,6 @@ local function from_lsp_location(loc, provider)
     text = loc.text,
     kind = loc.kind,
     provider = provider,
-    origin = loc.originSelectionRange,
   }
 end
 
@@ -224,6 +225,122 @@ function M.list_from_lsp(result, provider)
   return items
 end
 
+---Find the loaded buffer for a URI, matching equivalent paths (symlinks,
+---differently escaped URIs) so unsaved buffer text wins over the file on disk.
+---@param uri string
+---@return integer?
+local function loaded_buf_for_uri(uri)
+  local fname = fs.uri_to_fname(uri)
+  local real = fname and resolve_realpath(fname)
+  for _, bufnr in ipairs(vim.api.nvim_list_bufs()) do
+    if vim.api.nvim_buf_is_loaded(bufnr) then
+      if vim.uri_from_bufnr(bufnr) == uri then
+        return bufnr
+      end
+      local name = vim.api.nvim_buf_get_name(bufnr)
+      if real and name ~= "" and resolve_realpath(name) == real then
+        return bufnr
+      end
+    end
+  end
+  return nil
+end
+
+---Return a reader for the 0-based lines of a document, preferring the loaded
+---buffer (which the LSP server sees) over the file on disk.
+---@param uri string
+---@return fun(row: integer): string?
+local function line_reader(uri)
+  local bufnr = loaded_buf_for_uri(uri)
+  if bufnr then
+    return function(row)
+      return vim.api.nvim_buf_get_lines(bufnr, row, row + 1, false)[1]
+    end
+  end
+
+  local lines
+  return function(row)
+    if not lines then
+      lines = {}
+      local fname = fs.uri_to_fname(uri)
+      local file = fname and io.open(fname, "rb")
+      if file then
+        for line in file:lines() do
+          -- Match the buffer text Neovim would show: no CR from CRLF files.
+          lines[#lines + 1] = line:gsub("\r$", "")
+        end
+        file:close()
+        if lines[1] then
+          lines[1] = lines[1]:gsub("^\239\187\191", "")
+        end
+      end
+    end
+    return lines[row + 1]
+  end
+end
+
+---Byte and LSP columns only differ on lines containing non-ASCII bytes.
+---@param line string?
+---@return boolean
+local function is_multibyte(line)
+  return line ~= nil and line:find("[\128-\255]") ~= nil
+end
+
+---@param read_line fun(row: integer): string?
+---@param pos { line: integer, character: integer }
+---@param encoding string
+---@return { line: integer, character: integer }
+local function position_to_byte(read_line, pos, encoding)
+  local line = read_line(pos.line)
+  if not is_multibyte(line) then
+    return { line = pos.line, character = pos.character }
+  end
+  return { line = pos.line, character = vim.str_byteindex(line, encoding, pos.character, false) }
+end
+
+---Convert a byte-column position in a loaded buffer into the column unit of
+---an LSP client's offset encoding.
+---@param bufnr integer
+---@param pos { line: integer, character: integer } 0-based line, byte column
+---@param encoding? string client offset encoding (defaults to "utf-16")
+---@return { line: integer, character: integer }
+function M.position_to_lsp(bufnr, pos, encoding)
+  encoding = encoding or "utf-16"
+  if encoding == "utf-8" then
+    return { line = pos.line, character = pos.character }
+  end
+  local line = vim.api.nvim_buf_get_lines(bufnr, pos.line, pos.line + 1, false)[1]
+  if not is_multibyte(line) then
+    return { line = pos.line, character = pos.character }
+  end
+  return { line = pos.line, character = vim.str_utfindex(line, encoding, pos.character, false) }
+end
+
+---Convert location ranges reported in an LSP client's offset encoding into
+---byte columns, the unit used for every internal location.
+---@param locations PeekstackLocation[]
+---@param encoding? string client offset encoding (defaults to "utf-16")
+function M.ranges_to_byte(locations, encoding)
+  encoding = encoding or "utf-16"
+  if encoding == "utf-8" then
+    return
+  end
+  ---@type table<string, fun(row: integer): string?>
+  local readers = {}
+  for _, loc in ipairs(locations) do
+    local reader = readers[loc.uri]
+    if not reader then
+      reader = line_reader(loc.uri)
+      readers[loc.uri] = reader
+    end
+    local range = normalize_range(loc.range)
+    loc.range = {
+      start = position_to_byte(reader, range.start, encoding),
+      ["end"] = position_to_byte(reader, range["end"], encoding),
+    }
+  end
+end
+
 ---@param diags table[]?
 ---@param provider? string
 ---@return PeekstackLocation[]

lua/peekstack/providers/lsp.lua

@@ -133,10 +133,7 @@ local function request(ctx, method, provider, params_modifier, result_mapper, cb
   for _, client in ipairs(clients) do
     local params = {
       textDocument = vim.lsp.util.make_text_document_params(bufnr),
-      position = {
-        line = ctx.position.line,
-        character = ctx.position.character,
-      },
+      position = location.position_to_lsp(bufnr, ctx.position, client.offset_encoding),
     }
     if params_modifier then
       params_modifier(params)
@@ -146,7 +143,13 @@ local function request(ctx, method, provider, params_modifier, result_mapper, cb
         return
       end
       if not err and result then
-        local ok, locs = pcall(mapper, result, provider, ctx)
+        local ok, locs = pcall(function()
+          local mapped = mapper(result, provider, ctx)
+          if type(mapped) == "table" then
+            location.ranges_to_byte(mapped, client.offset_encoding)
+          end
+          return mapped
+        end)
         if ok and type(locs) == "table" then
           vim.list_extend(all_locations, locs)
         end

lua/peekstack/types.lua

@@ -1,4 +1,6 @@
 -- Type definitions for Peekstack
+---0-based lines and 0-based byte columns. LSP providers convert from and to
+---each client's offset encoding at the request boundary.
 ---@class PeekstackRange
 ---@field start { line: integer, character: integer }
 ---@field ["end"] { line: integer, character: integer }
@@ -9,7 +11,6 @@
 ---@field text? string
 ---@field kind? integer
 ---@field provider string
----@field origin? PeekstackRange
 
 ---@class PeekstackDiagnosticExtmarks
 ---@field bufnr integer
@@ -156,7 +157,7 @@
 ---@field popup_id integer?
 ---@field buffer_mode "copy"|"source"|nil
 ---@field line_offset integer
----@field position { line: integer, character: integer }
+---@field position { line: integer, character: integer } 0-based line and byte column in `bufnr`
 ---@field root_winid integer
 ---@field from_popup boolean
 

tests/location_spec.lua

@@ -36,6 +36,24 @@ describe("location", function()
       assert.equals(3, result.range.start.line)
     end)
 
+    it("prefers targetSelectionRange over targetRange for a LocationLink", function()
+      local loc = {
+        targetUri = "file:///tmp/bar.lua",
+        targetRange = {
+          start = { line = 3, character = 0 },
+          ["end"] = { line = 9, character = 3 },
+        },
+        targetSelectionRange = {
+          start = { line = 3, character = 9 },
+          ["end"] = { line = 3, character = 14 },
+        },
+      }
+      local result = location.normalize(loc, "lsp.definition")
+      assert.is_not_nil(result)
+      assert.same({ line = 3, character = 9 }, result.range.start)
+      assert.same({ line = 3, character = 14 }, result.range["end"])
+    end)
+
     it("normalizes a filename-based location", function()
       local loc = {
         filename = "/tmp/test.lua",