GULPF

proc foo(x: int8) = discard
proc bar(x: range[0'i8..1'i8]) = discard

var x = 1.int

echo compiles(foo(x)) # false
echo compiles(bar(x)) # true

GULPF

NOTE: The imports are found by simple walking throught the AST and looking after `nkFromStmt` and `nkImportStmt` nodes.
The stdlib modules are identified by simple string comparisions.
This method is not entirely accurate, but it does give some indication of which modules are used and which are not.

File imports (tot: 14078)
0 volatile
0 db_odbc
0 asyncftpclient
0 punycode
0 ssl

GULPF

import typetraits

iterator foo(i: int): int {.closure.} =
  yield i + 1
  yield i + 2

let f = foo
echo f(1) # 2
echo f(2) # 4

GULPF

import random, times

var input = newSeq[string]()
for _ in 1..100_000:
    input.add(fromUnix(rand(0..100_000_000)).utc.format("yyyy-MM-dd'T'HH:mm:sszzz"))

block:
    var sum = 0'i64
    let before = getTime()
    for str in input:

GULPF

Number of files that imports the module (~15000 files total)
1 oswalkdir
1 rstgen
1 ftpclient
1 distros
1 strmisc
2 rlocks
2 lenientops
2 unidecode
3 httpserver