-- luainspect.init - core LuaInspect source analysis.
--
-- This module is a bit more high level than luainspect.ast.  It deals more with
-- interpretation/inference of semantics of an AST.  It also uses luainspect.globals,
-- which does the basic semantic interpretation of globals/locals.
--
-- (c) 2010 David Manura, MIT License.

local M = {}

-- This is the API version.  It is an ISO8601 date expressed as a fraction.
M.APIVERSION = 0.20100805

local LA = require "luainspect.ast"
local LD = require "luainspect.dump"
local LG = require "luainspect.globals"
local LS = require "luainspect.signatures"
local T = require "luainspect.types"
local COMPAT = require "luainspect.compat_env"

--! require 'luainspect.typecheck' (context)

local ENABLE_RETURN_ANALYSIS = true
local DETECT_DEADCODE = false -- may require more validation (false positives)


-- Functional forms of Lua operators.
-- Note: variable names like _1 are intentional.  These affect debug info and
-- will display in any error messages.
local ops = {}
ops['add'] = function(_1,_2) return _1+_2 end
ops['sub'] = function(_1,_2) return _1-_2 end
ops['mul'] = function(_1,_2) return _1*_2 end
ops['div'] = function(_1,_2) return _1/_2 end
ops['mod'] = function(_1,_2) return _1%_2 end
ops['pow'] = function(_1,_2) return _1^_2 end
ops['concat'] = function(_1,_2) return _1.._2 end
ops['eq'] = function(_1,_2) return _1==_2 end
ops['lt'] = function(_1,_2) return _1<_2 end
ops['le'] = function(_1,_2) return _1<=_2 end
ops['and'] = function(_1,_2) return _1 and _2 end
ops['or'] = function(_1,_2) return _1 or _2 end
ops['not'] = function(_1) return not _1 end
ops['len'] = function(_1) return #_1 end
ops['unm'] = function(_1) return -_1 end


-- Performs binary operation.  Supports types.
local function dobinop(opid, a, b)
  if (a == T.number or b == T.number) and
     (a == T.number or type(a) == 'number' ) and
     (b == T.number or type(b) == 'number' )
  then
    if opid == 'eq' or opid == 'lt' or opid == 'le' then
      return T.boolean
    elseif opid == 'concat' then
      return T.string
    else
      return T.number
    end
  elseif (a == T.string or b == T.string) and
           (a == T.string or type(a) == 'string' ) and
           (b == T.string or type(b) == 'string' )
  then
    if opid == 'concat' or opid == 'and' or opid == 'or' then
      return T.string
    elseif opid == 'eq' or opid == 'lt' or opid == 'le' then
      return T.boolean
    else
      return T.number
    end
  elseif (a == T.boolean or b == T.boolean) and
           (a == T.boolean or type(a) == 'boolean' ) and
           (b == T.boolean or type(b) == 'boolean' )
  then
    if opid == 'eq' or opid == 'and' or opid == 'or' then
      return T.boolean
    else
      error('invalid operation on booleans: ' .. opid, 0)
    end
  elseif T.istype[a] or T.istype[b] then
    return T.universal
  else
    return ops[opid](a, b)
  end
end


-- Performs unary operation.  Supports types.
local function dounop(opid, a)
  if opid == 'not' then
    if T.istype[a] then
      return T.boolean
    else
      return ops[opid](a)
    end
  elseif a == T.number then
    if opid == 'unm' then
      return T.number
    else -- 'len'
      error('invalid operation on number: ' .. opid, 0)
    end
  elseif a == T.string then
    return T.number
  elseif a == T.boolean then
    error('invalid operation on boolean: ' .. opid, 0)
  elseif T.istype[a] then
    return nil, 'unknown'
  else
    return ops[opid](a)
  end
end

-- Like info in debug.getinfo but inferred by static analysis.
-- object -> {fpos=fpos, source="@" .. source, fast=ast, tokenlist=tokenlist}
-- Careful: value may reference key (affects pre-5.2 which lacks emphemerons).
--   See also ast.nocollect.
M.debuginfo = setmetatable({}, {__mode='v'})

-- Modules loaded via require_inspect.
-- module name string -> {return value, AST node}
-- note: AST node is maintained to prevent nocollect fields in ast being collected.
-- note: not a weak table.
M.package_loaded = {}

-- Stringifies interpreted value for debugging.
-- CATEGORY: debug
local function debugvalue(ast)
  local s
  if ast then
    s = ast.value ~= T.universal and 'known:' .. tostring(ast.value) or 'unknown'
  else
    s = '?'
  end
  return s
end


-- Reads contents of text file in path, in binary mode.
-- On error, returns nil and error message.
local function readfile(path)
  local fh, err = io.open(path, 'rb')
  if fh then
    local data; data, err = fh:read'*a'
    if data then return data end
  end
  return nil, err
end

-- Similar to string.gsub but with plain replacement (similar to option in string.match)
-- http://lua-users.org/lists/lua-l/2002-04/msg00118.html
-- CATEGORY: utility/string
local function plain_gsub(s, pattern, repl)
  repl = repl:gsub('(%%)', '%%%%')
  return s:gsub(pattern, repl)
end

-- Infer name of variable or literal that AST node represents.
-- This is for debugging messages.
local function infer_name(ast)
  if ast == nil then return nil
  elseif ast.tag == 'Id' then return "'"..ast[1].."'"
  elseif ast.tag == 'Number' then return 'number'
  elseif ast.tag == 'String' then return 'string'
  elseif ast.tag == 'True' then return 'true'
  elseif ast.tag == 'False' then return 'false'
  elseif ast.tag == 'Nil' then return 'nil'
  else return nil end
end

--[[
 This is like `pcall` but any error string returned does not contain the
 "chunknamem:currentline: " prefix (based on luaL_where) if the error occurred
 in the current file.  This avoids error messages in user code (f)
 being reported as being inside this module if this module calls user code.
 Also, local variable names _1, _2, etc. in error message are replaced with names
 inferred (if any) from corresponding AST nodes in list `asts` (note: nil's in asts skip replacement).
--]]
local _prefix
local _clean
local function pzcall(f, asts, ...)
  _prefix = _prefix or select(2, pcall(function() error'' end)):gsub(':%d+: *$', '') -- note: specific to current file.
  _clean = _clean or function(asts, ok, ...)
    if ok then return true, ...
    else
      local err = ...
      if type(err) == 'string' then
        if err:sub(1,#_prefix) == _prefix then
          local more = err:match('^:%d+: *(.*)', #_prefix+1)
          if more then
            err = more
            err = err:gsub([[local '_(%d+)']], function(name) return infer_name(asts[tonumber(name)]) end)
          end
        end
      end
      return ok, err
    end
  end
  return _clean(asts, pcall(f, ...))
end

-- Loads source code of given module name.
-- Returns code followed by path.
-- note: will also search in the directory `spath` and its parents.
--   This should preferrably be an absolute path or it might not work correctly.
--   It must be slash terminated.
-- CATEGORY: utility/package
local function load_module_source(name, spath)
  -- Append parent directories to list of paths to search.
  local package_path = package.path
  local ppath = spath
  repeat
    package_path = package_path .. ';' .. ppath .. '?.lua;' .. ppath .. '?/init.lua'
    local nsub
    ppath, nsub = ppath:gsub('[^\\/]+[\\/]$', '')
  until nsub == 0

  for spec in package_path:gmatch'[^;]+' do
    local testpath = plain_gsub(spec, '%?', (name:gsub('%.', '/')))
    local src, err_ = readfile(testpath)
    if src then return src, testpath end
  end
  return nil
end


-- Clears global state.
-- This includes cached inspected modules.
function M.clear_cache()
  for k,v in pairs(M.package_loaded) do
    M.package_loaded[k] = nil
  end
end


-- Gets all keywords related to AST `ast`, where `top_ast` is the root of `ast`
-- and `src` is source code of `top_ast`
-- Related keywords are defined as all keywords directly associated with block containing node
-- `ast`.  Furthermore, break statements are related to containing loop statements,
-- and return statements are related to containing function statement (if any).
-- function declaration syntactic sugar is handled specially too to ensure the 'function' keyword
-- is highlighted even though it may be outside of the `Function AST.
--
-- Returns token list or nil if not applicable.  Returned `ast` is AST containing related keywords.
-- CATEGORY: keyword comprehension
local iskeystat = {Do=true, While=true, Repeat=true, If=true, Fornum=true, Forin=true,
    Local=true, Localrec=true, Return=true, Break=true, Function=true,
    Set=true -- note: Set for `function name`
}
local isloop = {While=true, Repeat=true, Fornum=true, Forin=true}
local isblock = {Do=true, While=true, Repeat=true, If=true, Fornum=true, Forin=true, Function=true}
function M.related_keywords(ast, top_ast, tokenlist, src)
  -- Expand or contract AST for certain contained statements.
  local more
  if ast.tag == 'Return' then
    -- if `return` selected, that consider containing function selected (if any)
    if not ast.parent then LA.mark_parents(top_ast) end
    local ancestor_ast = ast.parent
    while ancestor_ast ~= nil and ancestor_ast.tag ~= 'Function' do
      ancestor_ast = ancestor_ast.parent
    end
    if ancestor_ast then ast = ancestor_ast end -- but only change if exists
  elseif ast.tag == 'Break' then
    -- if `break` selected, that consider containing loop selected
    if not ast.parent then LA.mark_parents(top_ast) end
    local ancestor_ast = ast.parent
    while ancestor_ast ~= nil and not isloop[ancestor_ast.tag] do
      ancestor_ast = ancestor_ast.parent
    end
    ast = ancestor_ast
  elseif ast.tag == 'Set' then
    local val1_ast = ast[2][1]
    if val1_ast.tag == 'Function' then
      local token = tokenlist[LA.ast_idx_range_in_tokenlist(tokenlist, ast)]
      if token.tag == 'Keyword' and token[1] == 'function' then -- function with syntactic sugar `function f`
        ast = ast[2][1] -- select `Function node
      else
        more = true
      end
    else
      more = true
    end
  elseif ast.tag == 'Localrec' and ast[2][1].tag == 'Function' then
    -- if `local function f` selected, which becomes a `Localrec, consider `Function node.
    ast = ast[2][1]
    --IMPROVE: only contract ast if `function` part of `local function` is selected.
  else
    more = true
  end
  if more then -- not yet handled
    -- Consider containing block.
    if not ast.parent then LA.mark_parents(top_ast) end
    local ancestor_ast = ast
    while ancestor_ast ~= top_ast and not isblock[ancestor_ast.tag] do
      ancestor_ast = ancestor_ast.parent
    end
    ast = ancestor_ast
  end

  --  keywords in statement/block.
  if iskeystat[ast.tag] then
    local keywords = {}
    for i=1,#tokenlist do
     local token = tokenlist[i]
     if token.ast == ast and token.tag == 'Keyword' then
       keywords[#keywords+1] = token
     end
    end

    -- Expand keywords for certaining statements.
    if ast.tag == 'Function' then
      -- if `Function, also select 'function' and 'return' keywords
      local function f(ast)
        for _,cast in ipairs(ast) do
          if type(cast) == 'table' then
            if cast.tag == 'Return' then
              local token = tokenlist[LA.ast_idx_range_in_tokenlist(tokenlist, cast)]
              keywords[#keywords+1] = token
            elseif cast.tag ~= 'Function' then f(cast) end
          end
        end
      end
      f(ast)
      if not ast.parent then LA.mark_parents(top_ast) end
      local grand_ast = ast.parent.parent
      if grand_ast.tag == 'Set' then
        local token = tokenlist[LA.ast_idx_range_in_tokenlist(tokenlist, grand_ast)]
        if token.tag == 'Keyword' and token[1] == 'function' then
          keywords[#keywords+1] = token
        end
      elseif grand_ast.tag == 'Localrec' then
        local tidx = LA.ast_idx_range_in_tokenlist(tokenlist, grand_ast)
        repeat tidx = tidx + 1 until not tokenlist[tidx] or (tokenlist[tidx].tag == 'Keyword' and tokenlist[tidx][1] == 'function')
        local token = tokenlist[tidx]
        keywords[#keywords+1] = token
      end
    elseif isloop[ast.tag] then
      -- if loop, also select 'break' keywords
      local function f(ast)
        for _,cast in ipairs(ast) do
          if type(cast) == 'table' then
            if cast.tag == 'Break' then
              local tidx = LA.ast_idx_range_in_tokenlist(tokenlist, cast)
              keywords[#keywords+1] = tokenlist[tidx]
            elseif not isloop[cast.tag]  then f(cast) end
          end
        end
      end
      f(ast)
    end

    return keywords, ast
  end
  return nil, ast
end


-- Mark tokenlist (top_ast/tokenlist/src) with keywordid AST attributes.
-- All keywords related to each other have the same keyword ID integer.
-- NOTE: This is not done/undone by inspect/uninspect.
-- CATEGORY: keyword comprehension
function M.mark_related_keywords(top_ast, tokenlist, src)
  local id = 0
  local idof = {}
  for _, token in ipairs(tokenlist) do
    if token.tag == 'Keyword' and not idof[token] then
      id = id + 1
      local match_ast =
        LA.smallest_ast_containing_range(top_ast, tokenlist, token.fpos, token.lpos)
      local ktokenlist = M.related_keywords(match_ast, top_ast, tokenlist, src)
      if ktokenlist then
         for _, ktoken in ipairs(ktokenlist) do
          ktoken.keywordid = id
          idof[ktoken] = true
        end
      end
      -- note: related_keywords may return a keyword set not containing given keyword.
    end
  end
end


-- function for t[k]
local function tindex(_1, _2) return _1[_2] end

local unescape = {['d'] = '.'}



-- Sets known value on ast to v if ast not pegged.
-- CATEGORY: utility function for infer_values.
local function set_value(ast, v)
  if not ast.isvaluepegged then
    ast.value = v
  end
end


local function known(o)
  return not T.istype[o]
end
local function unknown(o)
  return T.istype[o]
end


-- CATEGORY: utility function for infer_values.
local function tastnewindex(t_ast, k_ast, v_ast)
  if known(t_ast.value) and known(k_ast.value) and known(v_ast.value) then
    local _1, _2, _3 = t_ast.value, k_ast.value, v_ast.value
    if _1[_2] ~= nil and _3 ~= _1[_2] then -- multiple values
      return T.universal
    else
      _1[_2] = _3
      return _3
    end
  else
    return T.universal
  end
end


-- Gets expected number of parameters for function (min, max) values.
-- In case of vararg, max is unknown and set to nil.
local function function_param_range(ast)
  local names_ast = ast[1]
  if #names_ast >= 1 and names_ast[#names_ast].tag == 'Dots' then
    return #names_ast-1, nil
  else
    return #names_ast, #names_ast
  end
end

-- Gets number of arguments to function call: (min, max) range.
-- In case of trailing vararg or function call, max is unknown and set to nil.
local function call_arg_range(ast)
  if ast.tag == 'Invoke' then
    if #ast >= 3 and
      (ast[#ast].tag == 'Dots' or ast[#ast].tag == 'Call' or ast[#ast].tag == 'Invoke')
    then
      return #ast-2, nil
    else
      return #ast-1, #ast-1
    end
  else
    if #ast >= 2 and
      (ast[#ast].tag == 'Dots' or ast[#ast].tag == 'Call' or ast[#ast].tag == 'Invoke')
    then
      return #ast-2, nil
    else
      return #ast-1, #ast-1
    end
  end
end


-- Reports warning. List of strings.
local function warn(report, ...)
  report('warning: ' .. table.concat({...}, ' '))
end

-- Reports status messages. List of strings.
local function status(report, ...)
  report('status: ' .. table.concat({...}, ' '))
end

-- unique value used to detect require loops (A require B require A)
local REQUIRE_SENTINEL = function() end

-- Gets single return value of chunk ast.  Assumes ast is inspected.
local function chunk_return_value(ast)
  local vinfo
      if ENABLE_RETURN_ANALYSIS then
        local info = M.debuginfo[ast.value]
        local retvals = info and info.retvals
        if retvals then
          vinfo = retvals[1]
        else
          vinfo = T.universal
        end
      else
        if ast[#ast] and ast[#ast].tag == 'Return' and ast[#ast][1] then
          vinfo = ast[#ast][1]
        else
          vinfo = T.universal
        end
      end
  return vinfo
end

-- Version of require that does source analysis (inspect) on module.
function M.require_inspect(name, report, spath)
  local plinfo = M.package_loaded[name]
  if plinfo == REQUIRE_SENTINEL then
     warn(report, "loop in require when loading " .. name)
     return nil
  end
  if plinfo then return plinfo[1] end
  status(report, 'loading:' .. name)
  M.package_loaded[name] = REQUIRE_SENTINEL -- avoid recursion on require loops
  local msrc, mpath = load_module_source(name, spath)
  local vinfo, mast
  if msrc then
    local err; mast, err = LA.ast_from_string(msrc, mpath)
    if mast then
      local mtokenlist = LA.ast_to_tokenlist(mast, msrc)
      M.inspect(mast, mtokenlist, msrc, report)
      vinfo = chunk_return_value(mast)
    else
      vinfo = T.error(err)
      warn(report, err, " ", mpath) --Q:error printing good?
    end
  else
    warn(report, 'module not found: ' .. name)
    vinfo = T.error'module not found' --IMPROVE: include search paths?
  end
  M.package_loaded[name] = {vinfo, mast}
  return vinfo, mast
end


-- Marks AST node and all children as dead (ast.isdead).
local function mark_dead(ast)
  LA.walk(ast, function(bast) bast.isdead = true end)
end

-- Gets list of `Return statement ASTs in `Function (or chunk) f_ast, not including
-- return's in nested functions.  Also returns boolean `has_implicit` indicating
-- whether function may return by exiting the function without a return statement.
-- Returns that are never exected are omitted (e.g. last return is omitted in
-- `function f() if x then return 1 else return 2 end return 3 end`).
-- Also marks AST nodes with ast.isdead (dead-code).
local function get_func_returns(f_ast)
  local isalwaysreturn = {}
  local returns = {}
  local function f(ast, isdead)
    for _,cast in ipairs(ast) do if type(cast) == 'table' then
      if isdead then mark_dead(cast) end -- even if DETECT_DEADCODE disabled
      if cast.tag ~= 'Function' and not isdead then -- skip nested functions
        f(cast, isdead) -- depth-first traverse
      end
      if ast.tag ~= 'If' and isalwaysreturn[cast] then isdead = true end
        -- subsequent statements in block never executed
    end end

    -- Code on walking up AST: propagate children to parents
    if ast.tag == 'Return' then
      returns[#returns+1] = ast
      isalwaysreturn[ast] = true
    elseif ast.tag == 'If' then
      if #ast%2 ~= 0 then -- has 'else' block
        local isreturn = true
        for i=2,#ast do
          if (i%2==0 or i==#ast) and not isalwaysreturn[ast[i]] then isreturn = nil; break end
        end
        isalwaysreturn[ast] = isreturn
      end
    else -- note: iterates not just blocks, but should be ok
      for i=1,#ast do
        if isalwaysreturn[ast[i]] then
          isalwaysreturn[ast] = true; break
        end
      end
    end
  end
  f(f_ast, false)
  local block_ast = f_ast.tag == 'Function' and f_ast[2] or f_ast
  local has_implicit = not isalwaysreturn[block_ast]
  return returns, has_implicit
end

-- temporary hack?
local function valnode_normalize(valnode)
  if valnode then
    return valnode.value
  else
    return T.none
  end
end


-- Gets return value at given return argument index, given list of `Return statements.
-- Return value is a superset of corresponding types in list of statements.
-- Example: {`Return{1,2,3}, `Return{1,3,'z'}} would return
-- 1, T.number, and T.universal for retidx 1, 2 and 3 respectively.
local function get_return_value(returns, retidx)
  if #returns == 0 then return T.none
  elseif #returns == 1 then
    return valnode_normalize(returns[1][retidx])
  else
    local combined_value = valnode_normalize(returns[1][retidx])
    for i=2,#returns do
      local cur_value = valnode_normalize(returns[i][retidx])
      combined_value = T.superset_types(combined_value, cur_value)
      if combined_value == T.universal then -- can't expand set further
          return combined_value
      end
    end
    return combined_value
    --TODO: handle values with possibly any number of return values, like f()
  end
end


-- Gets return values (or types) on `Function (or chunk) represented by given AST.
local function get_func_return_values(f_ast)
  local returns, has_implicit = get_func_returns(f_ast)
  if has_implicit then returns[#returns+1] = {tag='Return'} end
  local returnvals = {n=0}
  for retidx=1,math.huge do
    local value = get_return_value(returns, retidx)
    if value == T.none then break end
    returnvals[#returnvals+1] = value
    returnvals.n = returnvals.n + 1
  end
  return returnvals
end
-- Example: AST of `function(x) if x then return 1,2,3 else return 1,3,"z" end end`
-- returns {1, T.number, T.universal}.


-- Given list of values, return the first nvalues values plus the rest of the values
-- as a tuple.   Useful for things like
--  local ok, values = valuesandtuple(1, pcall(f))
-- CATEGORY: utility function (list)
local function valuesandtuple(nvalues, ...)
  if nvalues >= 1 then
    return (...), valuesandtuple(nvalues-1, select(2, ...))
  else
    return {n=select('#', ...), ...}
  end
end


-- Infers values of variables. Also marks dead code (ast.isdead).
--FIX/WARNING - this probably needs more work
-- Sets top_ast.valueglobals, ast.value, ast.valueself
-- CATEGORY: code interpretation
function M.infer_values(top_ast, tokenlist, src, report)
  if not top_ast.valueglobals then top_ast.valueglobals = {} end


  -- infer values
  LA.walk(top_ast, function(ast) -- walk down
    if ast.tag == 'Function' then
      local paramlist_ast = ast[1]
      for i=1,#paramlist_ast do local param_ast = paramlist_ast[i]
        if param_ast.value == nil then param_ast.value = T.universal end
      end
    end
  end, function(ast) -- walk up
    -- process `require` statements.
    if ast.tag == 'Local' or ast.tag == 'Localrec' then
      local vars_ast, values_ast = ast[1], ast[2]
      local valuelist = #values_ast > 0 and values_ast[#values_ast].valuelist
      for i=1,#vars_ast do
        local var_ast, value_ast = vars_ast[i], values_ast[i]
        local value
        if value_ast then
          value = value_ast.value
        elseif valuelist then
          local vlidx = i - #values_ast + 1
          value = valuelist.sizeunknown and vlidx > valuelist.n and T.universal or valuelist[vlidx]
        end
        set_value(var_ast, value)
      end
    elseif ast.tag == 'Set' then -- note: implementation similar to 'Local'
      local vars_ast, values_ast = ast[1], ast[2]
      local valuelist = #values_ast > 0 and values_ast[#values_ast].valuelist
      for i=1,#vars_ast do
        local var_ast, value_ast = vars_ast[i], values_ast[i]
        local value
        if value_ast then
          value = value_ast.value
        elseif valuelist then
          local vlidx = i - #values_ast + 1
          value = valuelist.sizeunknown and vlidx > valuelist.n and T.universal or valuelist[vlidx]
        end
        if var_ast.tag == 'Index' then
          local t_ast, k_ast = var_ast[1], var_ast[2]
          if not T.istype[t_ast.value] then -- note: don't mutate types
            local v_ast = {value=value}
            local ok;  ok, var_ast.value = pzcall(tastnewindex, {t_ast, k_ast, v_ast}, t_ast, k_ast, v_ast)
            if not ok then var_ast.value = T.error(var_ast.value) end
              --FIX: propagate to localdefinition?
          end
        else
          assert(var_ast.tag == 'Id', var_ast.tag)
          if var_ast.localdefinition then
            set_value(var_ast, value)
          else -- global
            local name = var_ast[1]
            top_ast.valueglobals[name] = value
          end
        end
        --FIX: propagate to definition or localdefinition?
      end
    elseif ast.tag == 'Fornum' then
      local var_ast = ast[1]
      set_value(var_ast, T.number)
    elseif ast.tag == 'Forin' then
      local varlist_ast, iter_ast = ast[1], ast[2]
      if #iter_ast == 1 and iter_ast[1].tag == 'Call' and iter_ast[1][1].value == ipairs then
        for i, var_ast in ipairs(varlist_ast) do
          if i == 1 then set_value(var_ast, T.number)
          -- handle the type of the value as the type of the first element
          -- in the table that is a parameter for ipairs
          elseif i == 2 then
            local t_ast = iter_ast[1][2]
            local value = T.universal
            if (known(t_ast.value) or T.istabletype[t_ast.value]) then
              local ok; ok, value = pzcall(tindex, {t_ast, {tag='Number', 1}}, t_ast.value, 1)
              if not ok then value = T.error(t_ast.value) end
            end
            set_value(var_ast, value)
          else set_value(var_ast, nil) end
        end
      elseif #iter_ast == 1 and iter_ast[1].tag == 'Call' and iter_ast[1][1].value == pairs then
        local t_ast = iter_ast[1][2]
        local value = T.universal
        local key
        if t_ast.value and (known(t_ast.value) or T.istabletype[t_ast.value]) then
          key = next(t_ast.value)
          local ok; ok, value = pzcall(tindex, {t_ast, {tag='String', key}}, t_ast.value, key)
          if not ok then value = T.error(t_ast.value) end
        end

        for i, var_ast in ipairs(varlist_ast) do
          if i == 1 then set_value(var_ast, type(key))
          elseif i == 2 then set_value(var_ast, value)
          else set_value(var_ast, nil) end
        end
      else -- general case, unknown iterator
        for _, var_ast in ipairs(varlist_ast) do
          set_value(var_ast, T.universal)
        end
      end
    elseif ast.tag == 'Id' then
      if ast.localdefinition then
        local localdefinition = ast.localdefinition
        if not localdefinition.isset then -- IMPROVE: support non-const (isset false) too
          set_value(ast, localdefinition.value)
        end
      else -- global
        local name = ast[1]
        local v = top_ast.valueglobals[name]
        if v ~= nil then
          ast.value = v
        else
          local ok; ok, ast.value = pzcall(tindex, {{tag='Id', '_G'}, {tag='String', name}}, _G, name)
          if not ok then ast.value = T.error(ast.value) end
        end
      end
    elseif ast.tag == 'Index' then
      local t_ast, k_ast = ast[1], ast[2]
      if (known(t_ast.value) or T.istabletype[t_ast.value]) and known(k_ast.value) then
        local ok; ok, ast.value = pzcall(tindex, {t_ast, k_ast}, t_ast.value, k_ast.value)
        if not ok then ast.value = T.error(ast.value) end
      end
    elseif ast.tag == 'Call' or ast.tag == 'Invoke' then
      -- Determine function to call (infer via index if method call).
      local isinvoke = ast.tag == 'Invoke'
      if isinvoke then
        local t, k = ast[1].value, ast[2].value
        if known(t) and known(k) then
          local ok; ok, ast.valueself = pzcall(tindex, {ast[1], ast[2]}, t, k)
          if not ok then ast.valueself = T.error(ast.valueself) end
        end
      end
      local func; if isinvoke then func = ast.valueself else func = ast[1].value end

      -- Handle function call.
      local argvalues_concrete = true; do  -- true iff all arguments known precisely.
        if #ast >= 2 then
          local firstargvalue; if isinvoke then firstargvalue = ast.valueself else firstargvalue = ast[2].value end
          if unknown(firstargvalue) then
            argvalues_concrete = false
          else  -- test remaining args
            for i=3,#ast do if unknown(ast[i].value) then argvalues_concrete = false; break end end
          end
        end
      end
      local found
      if known(func) and argvalues_concrete then -- attempt call with concrete args
        -- Get list of values of arguments.
        local argvalues; do
          argvalues = {n=#ast-1}; for i=1,argvalues.n do argvalues[i] = ast[i+1].value end
          if isinvoke then argvalues[1] = ast.valueself end -- `self`
        end
        -- Any call to require is handled specially (source analysis).
        if func == require and type(argvalues[1]) == 'string' then
          local spath = tostring(ast.lineinfo.first):gsub('<C|','<'):match('<([^|]+)') -- a HACK? relies on AST lineinfo
          local val, mast = M.require_inspect(argvalues[1], report, spath:gsub('[^\\/]+$', ''))
          if known(val) and val ~= nil then
            ast.value = val
            found = true
          end -- note: on nil value, assumes analysis failed (not found). This is a heuristic only.
          if mast and mast.valueglobals then ast.valueglobals = mast.valueglobals end
        end
        -- Attempt call if safe.
        if not found and (LS.safe_function[func] or func == pcall and LS.safe_function[argvalues[1]]) then
          local ok; ok, ast.valuelist = valuesandtuple(1, pcall(func, unpack(argvalues,1,argvalues.n)))
          ast.value = ast.valuelist[1]; if not ok then ast.value = T.error(ast.value) end
          found = true
        end
      end
      if not found then
        -- Attempt mock function.  Note: supports nonconcrete args too.
        local mf = LS.mock_functions[func]
        if mf then
          ast.valuelist = mf.outputs; ast.value = ast.valuelist[1]
        else
          -- Attempt infer from return statements in function source.
          local info = M.debuginfo[func]
          if not info then -- try match from dynamic debug info
            local dinfo = type(func) == 'function' and debug.getinfo(func)
            if dinfo then
              local source, linedefined = dinfo.source, dinfo.linedefined
              if source and linedefined then
                local sourceline = source .. ':' .. linedefined
                info = M.debuginfo[sourceline]
              end
            end
          end
          local retvals = info and info.retvals
          if retvals then
            ast.valuelist = retvals; ast.value = ast.valuelist[1]
          else
            -- Could not infer.
            ast.valuelist = {n=0, sizeunknown=true}; ast.value = T.universal
          end
        end
      end
    elseif ast.tag == 'String' or ast.tag == 'Number' then
      ast.value = ast[1]
    elseif ast.tag == 'True' or ast.tag == 'False' then
      ast.value = (ast.tag == 'True')
    elseif ast.tag == 'Function' or ast == top_ast then -- includes chunk
      if ast.value == nil then -- avoid redefinition
        local x
        local val = function() x=nil end
        local fpos = LA.ast_pos_range(ast, tokenlist)
        local source, linenum = tostring(ast.lineinfo.first):gsub('<C|','<'):match('<([^|]+)|L(%d+)') -- a HACK? relies on AST lineinfo
        local retvals
        if ENABLE_RETURN_ANALYSIS then
          retvals = get_func_return_values(ast) --Q:move outside of containing conditional?
        end
        local info = {fpos=fpos, source="@" .. source, fast=ast, tokenlist=tokenlist, retvals=retvals, top_ast = top_ast}
        M.debuginfo[val] = info
        local sourceline = '@' .. source .. ':' .. linenum
        local oldinfo = M.debuginfo[sourceline]
        if oldinfo then
          if oldinfo.fast ~= ast then
            -- Two functions on the same source line cannot necessarily be disambiguated.
            -- Unfortuntely, Lua debuginfo lacks exact character position.
            --   http://lua-users.org/lists/lua-l/2010-08/msg00273.html
            -- So, just disable info if ambiguous.  Note: a slight improvement is to use the lastlinedefined.
            M.debuginfo[sourceline] = false
          end
        else
          if oldinfo == nil then
            M.debuginfo[sourceline] = info  -- store by sourceline too for quick lookup from dynamic debug info
          end  -- else false (do nothing)
        end
        ast.value = val
        ast.nocollect = info -- prevents garbage collection while ast exists
      end
    elseif ast.tag == 'Table' then
      if ast.value == nil then -- avoid redefinition
        local value = {}
        local n = 1
        for _,east in ipairs(ast) do
          if east.tag == 'Pair' then
            local kast, vast = east[1], east[2]
            if known(kast.value) and known(vast.value) then
              if kast.value == nil then
                -- IMPROVE? warn in some way?
              else
                value[kast.value] = vast.value
              end
            end
          else
            if known(east.value) then
              value[n] = east.value
            end
            n = n + 1
          end
        end
        --table.foreach(value, print)
        ast.value = value
      end
    elseif ast.tag == 'Paren' then
      ast.value = ast[1].value
    elseif ast.tag == 'Op' then
      local opid, aast, bast = ast[1], ast[2], ast[3]
      local ok
      if bast then
        ok, ast.value = pzcall(dobinop, {aast, bast}, opid, aast.value, bast.value)
      else
        ok, ast.value = pzcall(dounop, {aast}, opid, aast.value)
      end
      if not ok then ast.value = T.error(ast.value) end
    elseif ast.tag == 'If' then
      -- detect dead-code
      if DETECT_DEADCODE then
        for i=2,#ast,2 do local valnode = ast[i-1]
          local bval = T.boolean_cast(valnode.value)
          if bval == false then -- certainly false
            mark_dead(ast[i])
          elseif bval == true then -- certainly true
            for ii=i+1,#ast do if ii%2 == 0 or ii==#ast then -- following blocks are dead
              mark_dead(ast[ii])
            end end
            break
          end
        end
      end
      -- IMPROVE? `if true return end; f()` - f could be marked as deadcode
    elseif ast.tag == 'While' then
      -- detect dead-code
      if DETECT_DEADCODE then
        local expr_ast, body_ast = ast[1], ast[2]
        if T.boolean_cast(expr_ast.value) == false then
          mark_dead(body_ast)
        end
      end
    end
  end)
end


-- Labels variables with unique identifiers.
-- Sets ast.id, ast.resolvedname
-- CATEGORY: code interpretation
function M.mark_identifiers(ast)
  local id = 0
  local seen_globals = {}
  LA.walk(ast, function(ast)
    if ast.tag == 'Id' or ast.isfield then
      if ast.localdefinition then
        if ast.localdefinition == ast then -- lexical definition
          id = id + 1
          ast.id = id
        else
          ast.id = ast.localdefinition.id
        end
      elseif ast.isfield then
        local previousid = ast.previous.id
        if not previousid then -- note: ("abc"):upper() has no previous ID
          id = id + 1
          previousid = id
        end
        local name = previousid .. '.' .. ast[1]:gsub('%%', '%%'):gsub('%.', '%d')
        if not seen_globals[name] then
          id = id + 1
          seen_globals[name] = id
        end
        ast.id = seen_globals[name]

        -- also resolve name
        local previousresolvedname = ast.previous.resolvedname
        if previousresolvedname then
          ast.resolvedname = previousresolvedname .. '.' .. ast[1]:gsub('%%', '%%'):gsub('%.', '%d')
        end
      else -- global
        local name = ast[1]
        if not seen_globals[name] then
          id = id + 1
          seen_globals[name] = id
        end
        ast.id = seen_globals[name]

        -- also resolve name
        ast.resolvedname = ast[1]
      end
    end
  end)
end


-- Environment in which to execute special comments (see below).
local env = setmetatable({}, {__index=_G})
env.context = env

env.number = T.number
env.string = T.string
env.boolean = T.boolean
env.error = T.error


-- Applies value to all identifiers with name matching pattern.
-- This command is callable inside special comments.
-- CATEGORY: code interpretation / special comment command
function env.apply_value(pattern, val)
  local function f(ast)
    if ast.tag == 'Id' and ast[1]:match(pattern) then
      ast.value = val; ast.isvaluepegged = true
    end
    for _,bast in ipairs(ast) do
      if type(bast) == 'table' then
        f(bast)
      end
    end
  end
  f(env.ast) -- ast from environment
  --UNUSED:
  -- for i=env.asti, #env.ast do
  --  local bast = env.ast[i]
  --  if type(bast) == 'table' then f(bast) end
  --end
end


-- Evaluates all special comments (i.e. comments prefixed by '!') in code.
-- This is similar to luaanalyze.
-- CATEGORY: code interpretation / special comments
function M.eval_comments(ast, tokenlist, report)
  local function eval(command, ast)
    --DEBUG('!', command:gsub('%s+$', ''), ast.tag)
    local f, err = COMPAT.load(command, nil, 't', env)
    if f then
      env.ast = ast
      local ok, err = pcall(f, ast)
      if not ok then warn(report, err, ': ', command) end
      env.ast = nil
   else
     warn(report, err, ': ', command)
    end
  end

  for idx=1,#tokenlist do
    local token = tokenlist[idx]
    if token.tag == 'Comment' then
      local command = token[1]:match'^!(.*)'
      if command then
        local mast = LA.smallest_ast_containing_range(ast, tokenlist, token.fpos, token.lpos)
        eval(command, mast)
      end
    end
  end
end
--IMPROVE: in `do f() --[[!g()]] h()` only apply g to h.




-- Partially undoes effects of inspect().
-- Note: does not undo mark_tag2 and mark_parents (see replace_statements).
-- CATEGORY: code interpretation
function M.uninspect(top_ast)
  -- remove ast from M.debuginfo
  for k, info in pairs(M.debuginfo) do
    if info and info.top_ast == top_ast then
      M.debuginfo[k] = nil
    end
  end

  -- Clean ast.
  LA.walk(top_ast, function(ast)
    -- undo inspect_globals.globals
    ast.localdefinition = nil
    ast.functionlevel = nil
    ast.isparam = nil
    ast.isset = nil
    ast.isused = nil
    ast.isignore = nil
    ast.isfield = nil
    ast.previous = nil
    ast.localmasked = nil
    ast.localmasking = nil

    -- undo mark_identifiers
    ast.id = nil
    ast.resolvedname = nil

    -- undo infer_values
    ast.value = nil
    ast.valueself = nil
    ast.valuelist = nil
    ast.isdead = nil   -- via get_func_returns
    ast.isvaluepegged = nil

    -- undo walk setting ast.seevalue
    ast.seevalue = nil

    -- undo walk setting ast.definedglobal
    ast.definedglobal = nil

    -- undo notes
    ast.note = nil

    ast.nocollect = nil

    -- undo infer_values
    ast.valueglobals = nil
  end)
end


-- Main inspection routine.  Inspects top_ast/tokenlist.
-- Error/status messages are sent to function `report`.
-- CATEGORY: code interpretation
function M.inspect(top_ast, tokenlist, src, report)
  --DEBUG: local t0 = os.clock()
  if not report then -- compat for older version of lua-inspect
    assert('inspect signature changed; please upgrade your code')
  end

  report = report or function() end

  local globals = LG.globals(top_ast)

  M.mark_identifiers(top_ast)

  M.eval_comments(top_ast, tokenlist, report)

  M.infer_values(top_ast, tokenlist, src, report)
  M.infer_values(top_ast, tokenlist, src, report) -- two passes to handle forward declarations of globals (IMPROVE: more passes?)

  -- Make some nodes as having values related to its parent.
  -- This allows clicking on `bar` in `foo.bar` to display
  -- the value of `foo.bar` rather than just "bar".
  LA.walk(top_ast, function(ast)
    if ast.tag == 'Index' then
      ast[2].seevalue = ast
    elseif ast.tag == 'Invoke' then
      ast[2].seevalue = {value=ast.valueself, parent=ast}
    end
  end)

  local function eval_name_helper(name)
    local var = _G
    for part in (name .. '.'):gmatch("([^.]*)%.") do
      part = part:gsub('%%(.)', unescape)
      if type(var) ~= 'table' and type(var) ~= 'userdata' then return nil end  --TODO:improve?
      var = var[part]
      if var == nil then return nil end
    end
    return var
  end
  local function eval_name(name)
    local ok, o = pzcall(eval_name_helper, {}, name)
    if ok then return o else return nil end
  end

  LA.walk(top_ast, function(ast)
    if top_ast ~= ast and ast.valueglobals then
      for k in pairs(ast.valueglobals) do globals[k] = {set = ast} end
      ast.valueglobals = nil
    end
    if ast.tag == 'Id' or ast.isfield then
      local vname = ast[1]
      --TODO: rename definedglobal to definedfield for clarity
      local atype = ast.localdefinition and 'local' or ast.isfield and 'field' or 'global'
      local definedglobal = ast.resolvedname and eval_name(ast.resolvedname) ~= nil or
                 atype == 'global' and (globals[vname] and globals[vname].set) or nil
      ast.definedglobal = definedglobal
      -- FIX: _G includes modules imported by inspect.lua, which is not desired
    elseif ast.tag == 'Call' or ast.tag == 'Invoke' then
      -- Argument count check.
      local value = ast.valueself or ast[1].value
      local info = M.debuginfo[value]
      local fast = info and info.fast
      if fast or LS.argument_counts[value] then
        local nparammin, nparammax
        if fast then
          nparammin, nparammax = function_param_range(info.fast)
        else
          nparammin, nparammax = unpack(LS.argument_counts[value])
        end
        local nargmin, nargmax = call_arg_range(ast)
        --print('DEBUG:', nparammin, nparammax, nargmin, nargmax)
        local iswarn
        local target_ast = ast.tag == 'Call' and ast[1] or ast[2]
        if (nargmax or math.huge) < nparammin then
          ast.note = "Too few arguments; "
          iswarn = true
        elseif nargmin > (nparammax or math.huge) then
          ast.note = "Too many arguments; "
          iswarn = true
        end
        if iswarn then
          ast.note = ast.note ..  "expected "
            .. nparammin .. (nparammax == nparammin and "" or " to " .. (nparammax or "infinity"))
            .. " but got "
            .. nargmin .. (nargmax == nargmin and "" or " to " .. (nargmax or "infinity")) .. "."
        end
      end
    end
  end)
end


-- Resolves identifier to value [*]
function M.resolve_id(id, scope, valueglobals, _G)
  local val
  if scope[id] then
    val = scope[id].value
  elseif valueglobals[id] ~= nil then
    val = valueglobals[id]
  else
    val = _G[id] -- assumes not raise
  end
  return val
end

-- Resolves prefix chain expression to value. [*]
-- On error returns nil and error object
function M.resolve_prefixexp(ids, scope, valueglobals, _G)
  local _1 = M.resolve_id(ids[1], scope, valueglobals, _G)
  local ok, err = pzcall(function()
    for i=2,#ids do
      _1 = _1[ids[i]]
    end
  end, {})
  if err then return nil, err or '?' end
  return _1
end

-- Gets local scope at given 1-indexed char position
function M.get_scope(pos1, ast, tokenlist)
  local mast, isafter = LA.current_statementblock(ast, tokenlist, pos1)
  local scope = LG.variables_in_scope(mast, isafter)
  return scope
end

-- Gets names in prefix expression ids (as returned by resolve_prefixexp). [*]
function M.names_in_prefixexp(ids, pos, ast, tokenlist)
  local scope = M.get_scope(pos, ast, tokenlist)
  --FIX: above does not handle `for x=1,2 do| print(x) end` where '|' is cursor position.
  local names = {}
  if #ids == 0 then -- global
    for name in pairs(scope) do names[#names+1] = name end
    for name in pairs(ast.valueglobals) do names[#names+1] = name end
    for name in pairs(_G) do names[#names+1] = name end
  else  -- field
    local t, err_ = M.resolve_prefixexp(ids, scope, ast.valueglobals, _G)
    if type(t) == 'table' then  -- note: err_ implies false here
      for name in pairs(t) do names[#names+1] = name end
    end
  end
  return names
end

-- Gets signature (function argument string or helpinfo string) on value.
-- Returns nil on not found.
function M.get_signature_of_value(value)
  local info = M.debuginfo[value] -- first try this
  if info and info.fast then
    local fidx, lidx = LA.ast_idx_range_in_tokenlist(info.tokenlist, info.fast[1])
    local ts = {}
    if fidx then
      for i=fidx,lidx do
        local token = info.tokenlist[i]
        ts[#ts+1] = token.tag == 'Dots' and '...' or token[1]
      end
    end
    local sig = 'function(' .. table.concat(ts, ' ') .. ')'
    if info.retvals then
      local vals = info.retvals
      local ts = {}
      if vals.n == 0 then
        sig = sig .. " no returns"
      else
        for i=1,vals.n do local val = vals[i]
          ts[#ts+1] = T.istype[val] and tostring(val) or LD.dumpstring(val) --Q:dumpstring too verbose?
        end
        sig = sig .. " returns " .. table.concat(ts, ", ")
      end
    end
    return sig
  end
  local sig = LS.value_signatures[value] -- else try this
  return sig
end


-- Gets signature (function argument string or helpinfo string) on variable ast.
-- Returns nil on not found.
function M.get_signature(ast)
  if known(ast.value) then
    return M.get_signature_of_value(ast.value)
  end
end


-- Gets 1-indexed character (or line) position and filename of
-- definition associated with AST node (if any).
function M.ast_to_definition_position(ast, tokenlist)
  local local_ast = ast.localdefinition
  local fpos, fline, path
  if local_ast then
    local tidx = LA.ast_idx_range_in_tokenlist(tokenlist, local_ast)
    if tidx then
      local spath = tostring(ast.lineinfo.first):gsub('<C|','<'):match('<([^|]+)') -- a HACK? using lineinfo
      fpos = tokenlist[tidx].fpos; path = spath
    end
  end
  if not fpos then
    local valueast = ast.seevalue or ast
    local val = valueast and valueast.value
    local info = M.debuginfo[val] or type(val) == 'function' and debug.getinfo(val)
    if info then
      if info.source:match'^@' then
        path = info.source:match'@(.*)'
        if info.linedefined then
          fline = info.linedefined
        else
          fpos = info.fpos
        end
      end
    end
  end
  return fpos, fline, path
end


-- Returns true iff value in ast node is known in some way.
function M.is_known_value(ast)
  local vast = ast.seevalue or ast
  return vast.definedglobal or known(vast.value) and vast.value ~= nil
end


-- Gets list of variable attributes for AST node.
function M.get_var_attributes(ast)
  local vast = ast.seevalue or ast
  local attributes = {}
  if ast.localdefinition then
    attributes[#attributes+1] = "local"
    if ast.localdefinition.functionlevel < ast.functionlevel then
      attributes[#attributes+1] = 'upvalue'
    end
    if ast.localdefinition.isparam then
      attributes[#attributes+1] = "param"
    end
    if not ast.localdefinition.isused then attributes[#attributes+1] = 'unused' end
    if ast.isignore then attributes[#attributes+1] = 'ignore' end
    if ast.localdefinition.isset then attributes[#attributes+1] = 'mutatebind'
    else attributes[#attributes+1] = 'constbind' end
    if ast.localmasking then
      attributes[#attributes+1] = "masking"
    end
    if ast.localmasked then
      attributes[#attributes+1] = "masked"
    end
  elseif ast.tag == 'Id' then -- global
    attributes[#attributes+1] = (M.is_known_value(vast) and "known" or "unknown")
    attributes[#attributes+1] = "global"
  elseif ast.isfield then
    attributes[#attributes+1] = (M.is_known_value(vast) and "known" or "unknown")
    attributes[#attributes+1] = "field"
  else
    attributes[#attributes+1] = "FIX" -- shouldn't happen?
  end
  if vast.parent and (vast.parent.tag == 'Call' or vast.parent.tag == 'Invoke')
         and vast.parent.note
  then
    attributes[#attributes+1] = 'warn'
  end
  return attributes
end


-- Gets detailed information about value in AST node, as string.
function M.get_value_details(ast, tokenlist, src)
  local lines = {}

  if not ast then return '?' end

  local vast = ast.seevalue or ast

  lines[#lines+1] = "attributes: " .. table.concat(M.get_var_attributes(ast), " ")

  lines[#lines+1] = "value: " .. tostring(vast.value)

  local sig = M.get_signature(vast)
  if sig then
    local kind = sig:find '%w%s*%b()$'  and 'signature' or 'description'
    lines[#lines+1] = kind .. ": " .. sig
  end

  local fpos, fline, path = M.ast_to_definition_position(ast, tokenlist)
  if fpos or fline then
    local fcol
    if fpos then
      fline, fcol = LA.pos_to_linecol(fpos, src)
    end
    local location = path .. ":" .. (fline) .. (fcol and ":" .. fcol or "")
    lines[#lines+1] = "location defined: " .. location
  end
  
  if ast.localdefinition and ast.localmasking then
      local fpos = LA.ast_pos_range(ast.localmasking, tokenlist)
      if fpos then
        local linenum = LA.pos_to_linecol(fpos, src)
        lines[#lines+1] = "masking definition at line: " .. linenum
      end
  end

  -- Render warning notes attached to calls/invokes.
  local note = vast.parent and (vast.parent.tag == 'Call' or vast.parent.tag == 'Invoke')
                    and vast.parent.note
  if note then
    lines[#lines+1] = "WARNING: " .. note
  end

  return table.concat(lines, "\n")
end


-- Gets list of all warnings, as strings.
-- In HTML Tidy format (which supports column numbers in SciTE, although is
-- slightly verbose and lacks filename).
function M.list_warnings(tokenlist, src)
  local warnings = {}
  local ttoken
  local function warn(msg)
    local linenum, colnum = LA.pos_to_linecol(ttoken.fpos, src)
    warnings[#warnings+1] = "line " .. linenum .. " column " .. colnum .. " - " .. msg
  end
  local isseen = {}
  for i,token in ipairs(tokenlist) do ttoken = token
    if token.ast then
      local ast = token.ast
      if ast.localmasking then
        local pos = LA.ast_pos_range(ast.localmasking, tokenlist)
        local linenum = pos and LA.pos_to_linecol(pos, src)
        warn("local " .. ast[1] .. " masks another local" .. (pos and " on line " .. linenum or ""))
      end
      if ast.localdefinition == ast and not ast.isused and not ast.isignore then
        warn("unused local " .. ast[1])
      end
      if ast.isfield and not(known(ast.seevalue.value) and ast.seevalue.value ~= nil) then
        warn("unknown field " .. ast[1])
      elseif ast.tag == 'Id' and not ast.localdefinition and not ast.definedglobal then
        warn("unknown global " .. ast[1])
      end
      local vast = ast.seevalue or ast
      local note = vast.parent and (vast.parent.tag == 'Call' or vast.parent.tag == 'Invoke')
                    and vast.parent.note
      if note and not isseen[vast.parent] then
        isseen[vast.parent] = true
        local esrc = LA.ast_to_text(vast.parent, tokenlist, src)
           -- IMPROVE: large items like `f(function() ... end)` may be shortened.
        warn(note .. (esrc and "for " .. esrc or ""))
      end
    end
  end
  return warnings
end


return M