runtime(vim): Cleanup syntax tests

Improve formatting and naming consistency of the syntax tests.

closes: #17850

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/input/vim_lambdas.vim

@@ -0,0 +1,135 @@
+" Vim lambda expressions
+" VIM_TEST_SETUP hi link vimLambdaOperator Todo
+" VIM_TEST_SETUP hi link vimLambdaBrace Todo
+" VIM_TEST_SETUP hi link vimFuncParam Identifier
+
+
+let expr = 42
+
+let Foo = {-> expr}
+let Foo = {_ -> expr}
+let Foo = {... -> expr}
+let Foo = {x -> expr}
+let Foo = {x, _ -> expr}
+let Foo = {x, ... -> expr}
+let Foo = {x, y -> expr}
+
+
+" Line continuations
+
+let Foo = {->
+      "\ comment
+      \ expr
+      \ }
+let Foo = {_ ->
+      "\ comment
+      \ expr
+      \ }
+let Foo = {... ->
+      "\ comment
+      \ expr
+      \ }
+let Foo = {x ->
+      \ expr
+      "\ comment
+      \ }
+let Foo = {x, y ->
+      "\ comment
+      \ expr
+      \ }
+
+let Foo = {
+      \ ->
+      "\ comment
+      \ expr
+      \ }
+let Foo = {x
+      \ ->
+      "\ comment
+      \ expr
+      \ }
+let Foo = {x, y
+      \ ->
+      "\ comment
+      \ expr
+      \ }
+
+let Foo = {x,
+      \ y,
+      \ z -> expr}
+
+let Foo = {
+      "\ comment
+      \ x,
+      "\ comment
+      \ y,
+      "\ comment
+      \ z
+      "\ comment
+      \ ->
+      "\ comment
+      \ expr
+      "\ comment
+      \ }
+
+let Foo = {-> [
+      \ 42,
+      \ 83
+      \]}
+
+let Foo = {-> {
+      \ 'a': 42,
+      \ 'b': 83
+      \}}
+
+let Foo = {-> #{
+      \ a: 42,
+      \ b: 83
+      \}}
+
+let Foo = {-> {->[
+      \ 42,
+      \ 83
+      \]}}
+
+let Foo = {-> {-> {
+      \ 'a': 42,
+      \ 'b': 83
+      \}}}
+
+let Foo = {-> {-> #{
+      \ a: 42,
+      \ b: 83
+      \}}}
+
+
+" :help lambda
+
+:let F = {arg1, arg2 -> arg1 - arg2}
+:echo F(5, 2)
+
+:let F = {-> 'error function'}
+:echo F('ignored')
+
+:function Foo(arg)
+:  let i = 3
+:  return {x -> x + i - a:arg}
+:endfunction
+:let Bar = Foo(4)
+:echo Bar(6)
+
+:echo map([1, 2, 3], {idx, val -> val + 1})
+" [2, 3, 4]  
+
+:echo sort([3,7,2,1,4], {a, b -> a - b})
+" [1, 2, 3, 4, 7]
+:let timer = timer_start(500,
+		\ {-> execute("echo 'Handler called'", "")},
+		\ {'repeat': 3})
+
+
+" Issue https://github.com/vim/vim/pull/17420#issuecomment-2927798687
+" (string immediately after -> operator)
+
+let [func, _func_] = [{->"func"}(), 'func']
+