feat: add Haddock documentation snippets with smart detection

Add two new snippets for generating Haddock documentation:

fdoc - Function documentation snippet:
- Auto-detects function name and type signature from line below cursor
- Parses parameter types to generate example placeholders
- Supports multiline type signatures (including name on separate line)
- Strips forall quantifiers (including nested)
- Strips type class constraints (single and tuple)
- Falls back to static placeholders when no signature detected

mdoc - Module documentation snippet:
- Auto-detects module name via LSP codelens or filename fallback
- Generates standard Haddock module header template

New utility functions in util.lua:
- strip_forall: Remove forall quantifiers from signatures
- strip_constraints: Remove type class constraints
- normalize_signature: Apply both transformations
- parse_type_signature: Parse signatures into params and return type
- parse_function_line: Parse function type declaration lines
- is_signature_continuation: Detect multiline signature continuations
- collect_multiline_signature: Join multiline signatures (supports both
  "name :: sig" and "name\n  :: sig" formats)
- get_function_context: Get function info from line below cursor

Also fixes a bug where _indent_newline crashed with "bad argument #2
to 'rep'" when parent buffer position was unavailable.

Includes 53 unit tests covering all new functionality.

Author: Agustin Jimenez

CHANGELOG.md

@@ -6,6 +6,32 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+
+- `fdoc` snippet: Haddock function documentation with smart signature detection.
+  Automatically detects function name and type signature from the line below cursor,
+  generating example placeholders with parameter types.
+- `mdoc` snippet: Haddock module documentation with smart module name detection.
+  Uses LSP codelens or filename as fallback.
+- `util.parse_type_signature`: Parse Haskell type signatures into parameter types
+  and return type, handling parentheses, brackets, and braces.
+- `util.parse_function_line`: Parse function type declaration lines.
+- `util.get_function_context`: Get function context from the line below cursor.
+- `util.strip_forall`: Strip forall quantifiers from type signatures.
+- `util.strip_constraints`: Strip type class constraints from type signatures.
+- `util.is_signature_continuation`: Detect multiline signature continuation lines.
+- `util.collect_multiline_signature`: Collect multiline type signatures.
+- Multiline type signature support for `fdoc` snippet.
+- Comprehensive tests for signature parsing, forall/constraint handling,
+  multiline signatures, and function context detection (49 tests).
+
+### Fixed
+
+- Handle nil parent position in `_indent_newline` that caused
+  "bad argument #2 to 'rep'" errors in snippets using dynamic indentation.
+
 ## [1.5.0] - 2025-10-06
 
 ### Added

lua/haskell-snippets/functions.lua

@@ -113,4 +113,48 @@ functions.lambda = s({
 })
 table.insert(functions.all, functions.lambda)
 
+local function get_fdoc_nodes()
+  local context = util.get_function_context()
+
+  if context then
+    local nodes = {
+      text('-- | `' .. context.name .. '` '),
+      insert(1, 'description.'),
+      text { '', '--', '-- Examples:', '--', '-- >>> ' .. context.name },
+    }
+
+    -- Add each parameter as an insert node
+    local idx = 2
+    for _, param in ipairs(context.params) do
+      table.insert(nodes, text(' '))
+      table.insert(nodes, insert(idx, param))
+      idx = idx + 1
+    end
+
+    table.insert(nodes, text { '', '-- ' })
+    table.insert(nodes, insert(idx, context.return_type))
+
+    return sn(nil, nodes)
+  end
+
+  -- Fallback to placeholders
+  return sn(nil, {
+    text('-- | '),
+    insert(1, 'Brief description.'),
+    text { '', '--', '-- Examples:', '--', '-- >>> ' },
+    insert(2, 'example'),
+    text { '', '-- ' },
+    insert(3, 'expected'),
+  })
+end
+
+---@type Snippet Haddock function documentation
+functions.fdoc = s({
+  trig = 'fdoc',
+  dscr = 'Haddock function documentation',
+}, {
+  dynamic(1, get_fdoc_nodes),
+})
+table.insert(functions.all, functions.fdoc)
+
 return functions

lua/haskell-snippets/module.lua

@@ -174,4 +174,27 @@ if has_haskell_parser then
   })
   table.insert(module.all, module.qualc)
 end
+
+local function get_mdoc_module_name_node()
+  local module_name = util.lsp_get_module_name() or get_buf_module_name()
+  if module_name then
+    return sn(nil, { text(module_name) })
+  end
+  return sn(nil, { insert(1, 'MyModule') })
+end
+
+---@type Snippet Haddock module documentation
+module.mdoc = s({
+  trig = 'mdoc',
+  dscr = 'Haddock module documentation',
+}, {
+  text { '-- |', '-- Module      : ' },
+  dynamic(1, get_mdoc_module_name_node),
+  text { '', '-- Description : ' },
+  insert(2, 'Short description here'),
+  text { '', '--', '-- ' },
+  insert(3, 'Longer description of the module.'),
+})
+table.insert(module.all, module.mdoc)
+
 return module