feat: apply changes as text edits using LSP utils (#18)

* feat: apply changes as text edits using LSP utils

This means we can leverage all of the work that was done in the LSP
client to preserve marks, cursor position, etc

* log: add trace logging to debug performance

* feat: use the same diff -> TextEdit technique for bad LSP servers

Some LSP servers simply return a single TextEdit that replaces the whole
buffer. This is bad for extmarks, cursor, and if the buffer is open in
multiple windows the non-active window will jump to the top. We can
detect that situation and apply the same vim.diff logic to convert it
into more granular TextEdits.

1 files changed, 122 insertions, 0 deletions

diff --git a/tests/fuzzer_spec.lua b/tests/fuzzer_spec.lua
new file mode 100644
index 0000000..81c032f
--- /dev/null
+++ b/tests/fuzzer_spec.lua
@@ -0,0 +1,122 @@
+require("plenary.async").tests.add_to_env()
+local test_util = require("tests.test_util")
+local conform = require("conform")
+local runner = require("conform.runner")
+
+describe("fuzzer", function()
+  before_each(function()
+    conform.formatters.test = {
+      meta = { url = "", description = "" },
+      command = "tests/fake_formatter.sh",
+    }
+  end)
+
+  after_each(function()
+    test_util.reset_editor()
+  end)
+
+  ---@param buf_content string[]
+  ---@param expected string[]
+  ---@param opts? table
+  local function run_formatter(buf_content, expected, opts)
+    local bufnr = vim.fn.bufadd("testfile")
+    vim.fn.bufload(bufnr)
+    vim.api.nvim_set_current_buf(bufnr)
+    vim.api.nvim_buf_set_lines(bufnr, 0, -1, true, buf_content)
+    vim.bo[bufnr].modified = false
+    runner.apply_format(0, buf_content, expected, nil, false)
+    -- We expect the last newline to be effectively "swallowed" by the formatter
+    -- because vim will use that as the EOL at the end of the file. The exception is that we always
+    -- expect at least one line in the output
+    if #expected > 1 and expected[#expected] == "" then
+      table.remove(expected)
+    end
+    assert.are.same(expected, vim.api.nvim_buf_get_lines(0, 0, -1, false))
+  end
+
+  local function make_word()
+    local chars = {}
+    for _ = 1, math.random(1, 10) do
+      table.insert(chars, string.char(math.random(97, 122)))
+    end
+    return table.concat(chars, "")
+  end
+
+  local function make_line()
+    local words = {}
+    for _ = 1, math.random(0, 6) do
+      table.insert(words, make_word())
+    end
+    return table.concat(words, " ")
+  end
+
+  local function make_file(num_lines)
+    local lines = {}
+    for _ = 1, math.random(1, num_lines) do
+      table.insert(lines, make_line())
+    end
+    return lines
+  end
+
+  local function do_insert(lines)
+    local idx = math.random(1, #lines + 1)
+    for _ = 1, math.random(1, 3) do
+      table.insert(lines, idx, make_line())
+    end
+  end
+
+  local function do_replace(lines)
+    local num_lines = math.random(1, math.min(3, #lines))
+    local idx = math.random(1, #lines - num_lines + 1)
+    local replacement = {}
+    local num_replace = math.random(1, 5)
+    for _ = 1, num_replace do
+      table.insert(replacement, make_line())
+    end
+    local col = math.random(1, lines[idx]:len())
+    replacement[1] = lines[idx]:sub(1, col) .. replacement[1]
+    col = math.random(1, lines[idx + num_lines - 1]:len())
+    replacement[#replacement] = replacement[#replacement] .. lines[idx + num_lines - 1]:sub(col)
+
+    for _ = 1, num_lines - num_replace do
+      table.remove(lines, idx)
+    end
+    for _ = 1, num_replace - num_lines do
+      table.insert(lines, idx, "")
+    end
+    for i = 1, num_replace do
+      lines[idx + i - 1] = replacement[i]
+    end
+  end
+
+  local function do_delete(lines)
+    local num_lines = math.random(1, 3)
+    local idx = math.random(1, #lines - num_lines)
+    for _ = 1, num_lines do
+      table.remove(lines, idx)
+    end
+  end
+
+  local function make_edits(lines)
+    lines = vim.deepcopy(lines)
+    for _ = 1, math.random(0, 3) do
+      do_insert(lines)
+    end
+    for _ = 1, math.random(0, 3) do
+      do_replace(lines)
+    end
+    for _ = 1, math.random(0, 3) do
+      do_delete(lines)
+    end
+    return lines
+  end
+
+  it("formats correctly", function()
+    for i = 1, 50000 do
+      math.randomseed(i)
+      local content = make_file(20)
+      local formatted = make_edits(content)
+      run_formatter(content, formatted)
+    end
+  end)
+end)