fix(highlight): resolve fenced info-string aliases so sh / js highlight

lua/md-render/display_utils.lua

@@ -62,6 +62,40 @@ function M.reset_osc8_cache()
   _osc8_supported = nil
 end
 
+-- Common info-string aliases that don't match a treesitter parser name directly.
+-- nvim-treesitter "main" branch and bare Neovim register no defaults, so without
+-- this table fenced blocks tagged ```sh / ```js / ... silently lose highlighting.
+-- Users can add more via vim.treesitter.language.register() — that path is tried
+-- first via vim.treesitter.language.get_lang().
+local LANG_ALIASES = {
+  sh = "bash",
+  shell = "bash",
+  shellscript = "bash",
+  zsh = "bash",
+  js = "javascript",
+  jsx = "javascript",
+  ts = "typescript",
+  py = "python",
+  rb = "ruby",
+  rs = "rust",
+  yml = "yaml",
+  md = "markdown",
+  ps1 = "powershell",
+}
+
+--- Resolve a fenced-block info string to a treesitter parser name.
+---@param name string
+---@return string
+local function resolve_lang(name)
+  local lower = name:lower()
+  local registered = vim.treesitter.language.get_lang(lower)
+  if registered and registered ~= lower then return registered end
+  return LANG_ALIASES[lower] or lower
+end
+
+M._resolve_lang = resolve_lang
+M._LANG_ALIASES = LANG_ALIASES
+
 --- Apply treesitter syntax highlighting to code blocks
 ---@param buf integer
 ---@param ns integer
@@ -82,13 +116,15 @@ function M.apply_treesitter_highlights(buf, ns, content)
     end
     local code_text = table.concat(code_lines, "\n")
 
-    local ok, parser = pcall(vim.treesitter.get_string_parser, code_text, block.language)
+    local lang = resolve_lang(block.language)
+
+    local ok, parser = pcall(vim.treesitter.get_string_parser, code_text, lang)
     if not ok or not parser then goto continue end
 
     local trees = parser:parse()
     if not trees or #trees == 0 then goto continue end
 
-    local query = vim.treesitter.query.get(block.language, "highlights")
+    local query = vim.treesitter.query.get(lang, "highlights")
     if not query then goto continue end
 
     for id, node in query:iter_captures(trees[1]:root(), code_text) do
@@ -117,7 +153,7 @@ function M.apply_treesitter_highlights(buf, ns, content)
       pcall(vim.api.nvim_buf_set_extmark, buf, ns, buf_sr, buf_sc, {
         end_row = buf_er,
         end_col = buf_ec,
-        hl_group = "@" .. name .. "." .. block.language,
+        hl_group = "@" .. name .. "." .. lang,
         priority = 4200,
       })
       ::skip_capture::

tests/display_utils_test.lua

@@ -0,0 +1,76 @@
+-- display_utils tests
+-- Run: nvim --headless -u NONE --noplugin -l tests/display_utils_test.lua
+
+package.path = vim.fn.getcwd() .. "/lua/?.lua;" .. vim.fn.getcwd() .. "/lua/?/init.lua;" .. package.path
+
+local display_utils = require "md-render.display_utils"
+
+local pass_count = 0
+local fail_count = 0
+
+local function assert_eq(actual, expected, msg)
+  if actual == expected then
+    pass_count = pass_count + 1
+  else
+    fail_count = fail_count + 1
+    print("FAIL: " .. msg)
+    print("  expected: " .. vim.inspect(expected))
+    print("  actual:   " .. vim.inspect(actual))
+  end
+end
+
+local function test(name, fn)
+  local ok, err = pcall(fn)
+  if not ok then
+    fail_count = fail_count + 1
+    print("ERROR: " .. name .. ": " .. tostring(err))
+  end
+end
+
+-- ============================================================================
+-- resolve_lang: map fenced info-string to treesitter parser name
+-- ============================================================================
+
+test("resolve_lang maps sh-family aliases to bash", function()
+  assert_eq(display_utils._resolve_lang "sh", "bash", "sh -> bash")
+  assert_eq(display_utils._resolve_lang "zsh", "bash", "zsh -> bash")
+  assert_eq(display_utils._resolve_lang "shell", "bash", "shell -> bash")
+  assert_eq(display_utils._resolve_lang "shellscript", "bash", "shellscript -> bash")
+end)
+
+test("resolve_lang maps common short forms", function()
+  assert_eq(display_utils._resolve_lang "js", "javascript", "js -> javascript")
+  assert_eq(display_utils._resolve_lang "jsx", "javascript", "jsx -> javascript")
+  assert_eq(display_utils._resolve_lang "ts", "typescript", "ts -> typescript")
+  assert_eq(display_utils._resolve_lang "py", "python", "py -> python")
+  assert_eq(display_utils._resolve_lang "rb", "ruby", "rb -> ruby")
+  assert_eq(display_utils._resolve_lang "rs", "rust", "rs -> rust")
+  assert_eq(display_utils._resolve_lang "yml", "yaml", "yml -> yaml")
+  assert_eq(display_utils._resolve_lang "md", "markdown", "md -> markdown")
+  assert_eq(display_utils._resolve_lang "ps1", "powershell", "ps1 -> powershell")
+end)
+
+test("resolve_lang is case-insensitive", function()
+  assert_eq(display_utils._resolve_lang "SH", "bash", "SH -> bash")
+  assert_eq(display_utils._resolve_lang "Bash", "bash", "Bash -> bash (passthrough)")
+end)
+
+test("resolve_lang passes through names with no alias", function()
+  assert_eq(display_utils._resolve_lang "bash", "bash", "bash stays bash")
+  assert_eq(display_utils._resolve_lang "lua", "lua", "lua stays lua")
+  assert_eq(display_utils._resolve_lang "go", "go", "go stays go")
+  assert_eq(display_utils._resolve_lang "unknown_xyz", "unknown_xyz", "unknown stays unknown")
+end)
+
+test("resolve_lang honors vim.treesitter.language.register", function()
+  -- Simulate a user-registered alias and confirm it wins over the literal name.
+  vim.treesitter.language.register("markdown", "custom_md_lang")
+  assert_eq(
+    display_utils._resolve_lang "custom_md_lang",
+    "markdown",
+    "registered alias custom_md_lang -> markdown"
+  )
+end)
+
+print(string.format("display_utils_test: %d passed, %d failed", pass_count, fail_count))
+if fail_count > 0 then os.exit(1) end