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9151 :: Weird behaviour from fmt in strformat library

• Cnerd (orginal) [2022-05-10T20:51:08+02:00] view original

  This template gives an error at the line where fmt is to be used to format a string with the keyword attempts

  template requestWrapper(client : HttpClient, url, body, status: string, headers: TableRef[string, seq[string]],
      reqtype : ReqType = Get, action: untyped) =
    
    var attempts : int
    
    ## If request TIMEOUT try again 5 times
    while true:
      
      try:
        
        ## do something
      
      except TimeoutError:
        
        if attempts < 5:
          
          error("Request TIMEOUT, trying again...")
          attempts.inc()
          continue
        
        fatal(fmt"Request TIMEOUT after {attempts} attempts, quitting..") ## This line gives an error
        quit(-1)
  Run

  The error :

  
  /home/cnerd/Documents/Pentesting/twitterapi/src/twitterapipkg/api.nim(126, 18) template/generic instantiation of `requestWrapper` from here
  /home/cnerd/Documents/Pentesting/twitterapi/src/twitterapipkg/api.nim(89, 16) template/generic instantiation of `fmt` from here
  /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/core/macros.nim(533, 1) Error: undeclared identifier: 'attempts'
  candidates (edit distance, scope distance); see '--spellSuggest':
   (4, 9): 'accept' [proc declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/pure/net.nim(1084, 6)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/pure/collections/sequtils.nim(1123, 10)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/pure/json.nim(822, 10)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(116, 10)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(126, 10)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(13, 10)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(233, 10)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(251, 10)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(30, 10)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(48, 10)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(57, 10)]
   (4, 9): 'items' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(6, 10)]
   (4, 9): 'mitems' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/pure/json.nim(828, 10)]
   (4, 9): 'mitems' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(23, 10)]
   (4, 9): 'mitems' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(242, 10)]
   (4, 9): 'mitems' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(260, 10)]
   (4, 9): 'mitems' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(39, 10)]
   (4, 9): 'mitems' [iterator declared in /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/iterators.nim(86, 10)]
         Tip: 3 messages have been suppressed, use --verbose to show them.
       Error: Build failed for package: twitterapi
          ... Execution failed with exit code 1
          ... Command: /home/cnerd/.nimble/bin/nim cpp --colors:on --noNimblePath --gc:arc --d:ssl --d:danger --d:release -d:NimblePkgVersion=0.1.0 --path:/home/cnerd/.nimble/pkgs/zippy-0.7.4 --hints:off -o:/home/cnerd/Documents/Pentesting/twitterapi/bin/twitterapi /home/cnerd/Documents/Pentesting/twitterapi/src/twitterapi.nim
  stack trace: (most recent call last)
  /tmp/nimblecache-1860451227/nimscriptapi_2618866954.nim(187, 16)
  /home/cnerd/Documents/Pentesting/twitterapi/twitterapi.nimble(19, 10) makeTask
  /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/nimscript.nim(273, 7) exec
  /home/cnerd/.choosenim/toolchains/nim-1.6.4/lib/system/nimscript.nim(273, 7) Error: unhandled exception: FAILED: nimble --gc:arc --d:ssl --d:danger --d:release build [OSError]
  Run

---

• Cnerd (orginal) [2022-05-10T20:53:34+02:00] view original

  When is substitute fmt for format from the strutils library it works well. I think the problem is from the way the fmt macro builds code. maybe it's ignoring the attempts variable while building the code

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• DavideGalilei (orginal) [2022-05-10T20:55:43+02:00] view original

  This is intended behavior, see https://nim-lang.org/docs/strformat.html#limitations

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• Cnerd (orginal) [2022-05-10T21:40:17+02:00] view original

  The variable attempts which the compiler claims is undefined is not part of the template arguments. it's a local variable declared inside of the template. So that limitation does not apply to this block of code

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• Yardanico (orginal) [2022-05-10T21:45:21+02:00] view original

  It does apply, just in a different way. fmt is expanded _after the template itself is expanded, and templates are hygienic by default, so attempts will be gensym'd so fmt can't find it. You can solve this by using inject, but then attempts will be visible from the code passed to the template.

  import std/strformat
  template requestWrapper() =
    var attempts {.inject.}: int
    
    echo fmt"test {attempts}"
  
  
  requestWrapper()
  Run

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• Cnerd (orginal) [2022-05-10T21:49:22+02:00] view original

  The inject pragma works, thanks @DavideGalilei and @Yardanico. By the way is this specific to variables or does it also affects let and consts

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• Yardanico (orginal) [2022-05-10T21:51:10+02:00] view original

  There's no difference in how var/let/const are treated in templates, in fact let and const are also called "variables" as well as var :)

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• shirleyquirk (orginal) [2022-05-11T10:18:34+02:00] view original

  to workaround injecting attempts into the containing scope you can wrap the template in a block:

  import std/strformat
  template requestWrapper() =
    block:
      var attempts {.inject.}: int
      
      echo fmt"test {attempts}"
  
  
  requestWrapper()
  requestWrapper()
  Run

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