symbol declared in template is considered undeclared if symbol with same name is injected into proc in same template

[jibal]

nim 1.2 on Windows 10

Error message:

x.nim(9, 1) template/generic instantiation of t from here
x.nim(7, 9) Error: undeclared identifier: 'x' [line is bod(x)]

from this code:

template t(body: untyped) =
  proc bod(a: int) =
    let x {.inject.} = a
    body
  
  let x = 1
  bod(x)

t:
  echo x

x is of course declared, contrary to the error message. The injected x is local to proc bod, and even if one of these x "overrides" the other (which makes no sense), the error message makes no sense -- there appears to be some sort of mishandling of the symbol table within the template. There's no error if the argument to bod doesn't reference x, or if the let is moved outside of the template, e.g.,

template t(body: untyped) =
  proc bod(a: int) =
    let x {.inject.} = a
    body
  
  bod(x)

let x = 1
t:
  echo x

This also works fine, as the two xs are not in the same template:

template z(body: untyped) =
  proc bod(a: int) =
    let x {.inject.} = a
    body

template t(body: untyped) =
  z(body)

  let x = 1
  bod(x)

t:
  echo x

[jibal]

Here's a further minimized failing example:

x.nim(8, 1) Error: undeclared identifier: 'x'
(This is the line invoking the template, unlike the other example where the error occurred at the point of use of x. Presumably this is because x isn't actually used inside the template; change line 6 from "x" to "x+1" and the error occurs there, as before.)

template t =
  proc p =
    let x {.inject.} = 1

  let x = 1
  x

t

Apparently, any use of a variable declared within the template with the same name as a symbol injected into the proc fails because the compiler erroneously thinks the symbol isn't declared.

[ghost]

Seems like a duplicate or really similar to #10609

[jibal]

Yes, it's the same. The dump in Bluenote10's comment on #10609 makes it evident that the inject in the proc causes subsequent uses (but not declarations) of gensymed symbols with the same name to be treated as if they are injected ... thus the x in my examples is undeclared because it is plain x, not the gensymed name that was declared with for or let. People in the forum noted that there's no error if the second x, outside the proc, is also injected ... which makes sense because then the bug isn't triggered ... the declared symbol and the used symbol match.

…

On Wed, Jun 10, 2020, 1:49 AM Danil Yarantsev ***@***.***> wrote: Duplicate or really similar to #10609 <#10609> maybe? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#14620 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAEDT2BBQJVWDDVJXCYJHE3RV5CJ3ANCNFSM4NZX573A> .

[jibal]

Here's an example that illustrates what's happening:

template t(body: untyped) =
  proc p =
    let x {.inject.} = 0

  let x = 1
  body
  echo x

t:
  let x = 2

This prints 2 rather than 1 because x in echo x uses the raw name rather than the gensymed name. This is a lot nastier than the examples that get errors ... you think your template is hygienic but it's not.