more informative error msg for undeclared field (A(badfield: 1) and a.badfield = expr)

[timotheecour]

followup #17745, #9766

type A = object
  x: int

when defined case1:
  type A2 = A
  var b: A
  let c = b.x2

when defined case2:
  let a = A(x: 1, y: 2)

when defined case3:
  var a: A
  a.x2 = 3

before PR:

case1: t12184.nim(28, 12) Error: undeclared field: 'x2' for type t12184.A [type declared in t12184.nim(22, 6)]
case2: t12184.nim(31, 20) Error: undeclared field: 'y'
case3: t12184.nim(35, 8) Error: attempting to call undeclared routine: 'x2='

after PR:

case1: t12184.nim(28, 12) Error: undeclared field: 'x2' for type t12184.A [type declared in t12184.nim(22, 6)]
case2: t12184.nim(31, 20) Error: undeclared field: 'y' for type t12184.A [type declared in t12184.nim(22, 6)]
case3: t12184.nim(35, 8) Error: undeclared field: 'x2' for type t12184.A [type declared in t12184.nim(22, 6)]

(in more complex cases it may not be obvious where the underlying object is declared)

future work

• similarly support generics eg: => followup #17777: declaredloc field error msgs now work with generics #18259

block:
  type Foo[T] = object
  var a: Foo[int]
  discard a.bad2 # should improve error
  a.bad2 = 0 # should improve error
  let a2 = Foo[int](bad: 0) # should improve error

[juancarlospaco]

The work on improving the error messages is appreciated.

[ringabout]

where is the test?

[timotheecour]

where is the test?

done, PTAL

[timotheecour]

ping @xflywind or @Araq