Block-local types with the same name lead to bad codegen (sighashes regression)

[nigredo-tori]

Example:

block:
  type Foo = object
    bar: bool
  var f1: Foo

block:
  type Foo = object
    baz: int
  var f2: Foo
  echo f2.baz

Leads to incorrect code generation:

Error: execution of an external compiler program 'gcc -c  -w  -I/home/nigredo/dev/nim/lib -o /home/nigredo/dev/tmp/nimcache/test_block_types.o /home/nigredo/dev/tmp/nimcache/test_block_types.c' failed with exit code: 1

/home/nigredo/dev/tmp/nimcache/test_block_types.c: In function ‘NimMainModule’:
/home/nigredo/dev/tmp/nimcache/test_block_types.c:113:47: error: ‘Foo_ERzUuJDwNMfy52HTAAjijQ {aka struct Foo_ERzUuJDwNMfy52HTAAjijQ}’ has no member named ‘baz’; did you mean ‘bar’?
   LOC3 = nimIntToStr(f2_lLsGauUAFcJDvAdQ34YRQA.baz);
                                               ^

Tested on: bf8f00f
Bisect points to: 860cbd3

[Araq]

Yeah but that is a known problem.

[andreaferretti]

Well, it used to work fine before the sighashes change

[timotheecour]

was gonna file a bug until I searched and found this... in my case it was a bit different, where the 1st type is not at block level but top-level:

  type Foo = object
    bar: bool
  var f1: Foo

  block:
    type Foo = object
      baz: int
    var f2: Foo
    echo f2.baz

=> same error

• it can also give obscure errors which only make sense once you know that bug:

  block:
    type Foo = object
      x1: int
    discard Foo()

  block:
    type Foo = object
      x1: array[5, int]
    var s = Foo()
    discard s.x1[0]

@mt1004.nim.c:140:39: error: subscripted value is not an array, pointer, or vector
(void)(s__VSi9cpJ72OTEoBvA6t4HEOQ.x1[(((NI) 0))- 0]);

• maybe same root cause as tuple codegen error #12704 but seems different

[narimiran]

Maybe obvious to y'all, but for me it wasn't: if you don't use the upper/outside object, or you use it after the block, it is ok:

type Foo = object
  bar: int8
var f1 = Foo(bar: 27)
echo f1.bar

block:
  type Foo = object
    bar: int
  var f2 = Foo(bar: 300)
  echo f2.bar

# 27
# 44

versus:

type Foo = object
  bar: int8

block:
  type Foo = object
    bar: int
  var f2 = Foo(bar: 300)
  echo f2.bar

var f1 = Foo(bar: 27)
echo f1.bar

# 300
# 27