neovim/scripts/lintcommit.lua

local function commit_message_is_ok(commit_message)
  local commit_split = vim.split(commit_message, ":")

  -- Return true if the type is vim-patch since most of the normal rules don't
  -- apply.
  if commit_split[1] == "vim-patch" then
    return true
  end

  -- Check that message isn't too long.
  if commit_message:len() > 80 then
    vim.cmd([[verbose echo "Commit message is too long, a maximum of 80 characters is allowed. Commit message:"]])
    return false
  end

  -- Return false if no colons are detected.
  if vim.tbl_count(commit_split) < 2 then
    vim.cmd([[verbose echo "Commit message does not include colons. Commit message:"]])
    return false
  end

  local before_colon = commit_split[1]
  local after_colon = commit_split[2]

  -- Check if commit introduces a breaking change.
  if vim.endswith(before_colon, "!") then
    before_colon = before_colon:sub(1, -2)
  end

  -- Check if type is correct
  local type = vim.split(before_colon, "%(")[1]
  local allowed_types = {"build", "ci", "docs", "feat", "fix", "perf", "refactor", "revert", "test", "chore"}
  if not vim.tbl_contains(allowed_types, type) then
    vim.cmd([[verbose echo "Commit type is not recognized. Allowed types are: build, ci, docs, feat, fix, perf, refactor, revert, test, chore. Commit message:"]])
    return false
  end

  -- Check if scope is empty
  if before_colon:match("%(") then
    local scope = vim.trim(before_colon:match("%((.*)%)"))
    if scope == '' then
      vim.cmd([[verbose echo "Scope can't be empty. Commit message:"]])
      return false
    end
  end

  -- Check that description doesn't end with a period
  if vim.endswith(after_colon, ".") then
      vim.cmd([[verbose echo "Description ends with a period (\".\"). Commit message:"]])
    return false
  end

  -- Check that description has exactly one whitespace after colon, followed by
  -- a lowercase letter and then any number of letters.
  if not string.match(after_colon, '^ %l%a*') then
      vim.cmd([[verbose echo "There should be one whitespace after the colon and the first letter should lowercase. Commit message:"]])
    return false
  end

  return true
end

local function main()
  local current_branch = vim.trim(vim.fn.system({'git', 'branch', '--show-current'}))
  local ancestor_commit = vim.trim(vim.fn.system({'git', 'merge-base', 'origin/master', current_branch}))
  local commits_str = vim.trim(vim.fn.system({'git', 'rev-list', ancestor_commit .. ".." .. current_branch}))

  local commits = {}
  for substring in commits_str:gmatch("%S+") do
     table.insert(commits, substring)
  end

  for _, commit_hash in ipairs(commits) do
    local message = vim.trim(vim.fn.system({'git', 'show', '-s', '--format=%s' , commit_hash}))
    if vim.v.shell_error ~= 0 then
      vim.cmd('verbose echo "Invalid commit-id: ' .. commit_hash .. '"')
    elseif not commit_message_is_ok(message) then
      vim.cmd("verbose echo '" .. message:gsub("'","''") .. "'")
      vim.cmd('verbose echo ""')
      vim.cmd("cquit 1")
    end
  end
end

local function _test()
  local good_messages = {
    "ci: normal message",
    "build: normal message",
    "docs: normal message",
    "feat: normal message",
    "fix: normal message",
    "perf: normal message",
    "refactor: normal message",
    "revert: normal message",
    "test: normal message",
    "chore: normal message",
    "ci(window): message with scope",
    "ci!: message with breaking change",
    "ci(tui)!: message with scope and breaking change",
    "vim-patch:8.2.3374: Pyret files are not recognized (#15642)",
    "vim-patch:8.1.1195,8.2.{3417,3419}",
  }

  local bad_messages = {
    ":no type before colon 1",
    " :no type before colon 2",
    "  :no type before colon 3",
    "ci(empty description):",
    "ci(whitespace as description): ",
    "docs(multiple whitespaces as description):   ",
    "ci no colon after type",
    "test:  extra space after colon",
    "ci:	tab after colon",
    "ci:no space after colon",
    "ci :extra space before colon",
    "refactor(): empty scope",
    "ci( ): whitespace as scope",
    "chore: period at end of sentence.",
    "ci: Starting sentence capitalized",
    "unknown: using unknown type",
    "chore: you're saying this commit message just goes on and on and on and on and on and on for way too long?",
  }

  print("Messages expected to pass:")

  for _, message in ipairs(good_messages) do
    if commit_message_is_ok(message) then
      print("[ PASSED ] :", message)
    else
      print("[ FAIL ]   :", message)
    end
  end

  print("Messages expected to fail:")

  for _, message in ipairs(bad_messages) do
    if commit_message_is_ok(message) then
      print("[ PASSED ] :", message)
    else
      print("[ FAIL ]   :", message)
    end
  end
end

-- _test()

main()