feat(lua): for / function snippets overhaul

[WieeRd]

Rewrite and add more snippets for the for statements and functions to cover more use cases.

For statements

Before

-- `for`
for i=1,10 do ... end

-- `foreach`
for i, x in pairs(table) do ... end

After

-- `for`
for ... do ... end

-- `forn` (for-numeric)
for i = 1, 10 do ... end

-- `fori` (for-ipairs)
for i, x in ipairs(t) ... end

-- `forp` (for-pairs)
for k, v in pairs(t) ... end

• for is now a generic for loop with zero assumption
• Added variants for 3 typical for loops: numeric range, array table, dictionary table
• Added spacing in numeric for: from i=1,10 to i = 1, 10
  • The latter seems predominant on most conventions and formatters.

Functions

Before

-- `fu` (function)
function name(args) ... end

-- `f=` (inline-function)
local name = function(args) ... end

After

-- `fu` (function)
function(args) ... end
--      ^ note: jump target with empty placeholder between `function` and `(`

-- `f=` (assign-function)
name = function(args) ... end

-- `lfu` (local-function)
local function name(args) ... end

-- `lf=` (local-assign-function)
local name = function(args) ... end

-- `f,` (member-function)
-- local tbl = {
       name = function(args) ... end,
--     existing_key_below = 42,
-- }

• *fu / *f= to support both function name() and name = function() style.
• fu: Removed space and name placeholder between function and (
  • This is in case the function is being used as an anonymous function (typically callbacks)

    vim.wait(300, function()
      print("300ms later")
    end)

  • The jump target itself still exists between function and (
• Obvious l* local variants
• member-function: Same as f= but with comma at the end,.
  If you assign a function to a key using f=, syntax highlights will be broken and the LSP complains until you finally insert the , after finishing writing the function.

Misc

Capitalized the descriptions of the snippets.

Not entirely sure about the styling / punctuation convention for the descriptions and names, though.
The CONTRIBUTING.md is missing, and I see no consistency in other language snippets I looked up for reference.
Some snippets are named foo-bar like here in lua.json, some are Foo bar, I don't know.

[WieeRd]

Maybe I should create a separate snippet for anonymous functions rather than emptying the name placeholder of fu, for consistency and convenience.

-- `fu` (function)
function name(args) ... end

-- `??` (anonymous-function)
function(args) ... end

What do you think? What should its prefix be?
I'm considering f) since f( would trigger auto pairs and turn into f().

[WieeRd]

Played around it, and it was a lot more convenient than having to tap twice using fu.