set equality silently gives wrong results instead of CT error for incompatible types

[timotheecour]

Example 1

when true:
  # xxx this fails in c, js, vm and gives cgen error in cpp
  # it should either give CT error or succeed (special casing literal)
  template main =
    block:
      var s1: set[char] = {'a', 'b'}
      var s2: set['a'..'z'] = {'a', 'b'}
      echo s2 == {'a', 'b'}
  static: main()
  main()

nim r main

Current Output

vm:true
js:true
c:false
cpp:cgen error:

/Users/timothee/git_clone/nim/timn/build/nimcache/@mt12496.nim.cpp:152:59: error: cast from pointer to smaller type 'tySet_tyChar__PvbCylXV13Xvtg1HZuvI8A' (aka 'unsigned int') loses information
                T2_[0] = nimBoolToStr((s2X60gensym1__t4950525754_17 == ((tySet_tyChar__PvbCylXV13Xvtg1HZuvI8A) (TM__PT0bVxrv4y8D21sJjCuaUw_2))));

Expected Output

option 1: CT error (simpler)
option 2: special case literals and return true in this case (using implicit conversion to LHS)

Example 2

this works fine:

when defined case2:
  template main =
    block:
      var s1: set[char] = {'a', 'b'}
      var s2: set['a'..'z'] = {'a', 'c'}
      doAssert not compiles(s1 + s2)
      doAssert not compiles(s2 + s1)
      doAssert not compiles(s1 == s2)
      doAssert not compiles(s2 == s1)
      doAssert s1 + s1 == s1
      doAssert s2 + s2 == s2
      doAssert s1 + s1 == {'a', 'b'}
  static: main()
  main()

Additional Information

• 1.5.1 36d2484
• related to Wrong result on operations on sets of different types #16270 which just got fixed

[metagn]

I'm guessing the issue here is that the literal type is pretending to be inferred as set['a'..'z'] but is becoming set[char] somehow. So it's #16270 for literals.