[obsolete] system module needs now shows a stacktrace (with debug nim)

[timotheecour]

• before this PR, all you get is a cryptic Error: system module needs: echoBinSafe with no backtrace (even with debug version of nim)
  as well as a wide choice of places where to look at:

compiler/cgen.nim:671:30:    internalError(m.config, "system module needs: " & name)
compiler/jsgen.nim:303:42:      globalError(p.config, p.prc.info, "system module needs: " & name)
compiler/jsgen.nim:305:43:      rawMessage(p.config, errGenerated, "system module needs: " & name)
compiler/lowerings.nim:290:33:    localError(g.config, info, "system module needs: " & name)
compiler/magicsys.nim:31:33:    localError(g.config, info, "system module needs: " & name)
compiler/magicsys.nim:47:31:  localError(g.config, info, "system module needs: " & name)

• after this PR, you get a backtrace (with debug version of nim)

This type of error can for example occur when refactoring system.nim; it's happening in #10559 but it also happened to me before (in my PR for {.nosystem.})

https://travis-ci.org/nim-lang/Nim/jobs/489276424

FAIL: tests/ccgbugs/twrongrefcounting.nim C
Test "tests/ccgbugs/twrongrefcounting.nim" in category "ccgbugs"
Failure: reNimcCrash
Expected:
Gotten:
system module needs: echoBinSafe

question to reviewer

besides what's fixed here, the only other place where a rawMessage is used with system module needs is:

    if p.prc != nil:
      globalError(p.config, p.prc.info, "system module needs: " & name)
    else:
      rawMessage(p.config, errGenerated, "system module needs: " & name)

seems like this should be changed to internalError as well, so as to get a backtrace?

[Araq]

Sorry but this is not a good solution. That is not an internal error, it's a misconfigured system.nim. We need to put more effort into this if we want to improve the error message like "; code generated for system.== [declared in line blah".

[Araq]

I don't understand this patch.

[timotheecour]

• it now shows a stacktrace in this case when compiling nim in debug mode, some change wrt note configuration must've fixed this
• if this ever regresses, compiling nim with -d:debug would show a stacktrace anyways (and would've worked back when this PR was made but it's easy to forget this undocumented(?) and hard to find because too generic define
• IMO we should change defined(debug) to isDefined(conf, "nimDebug") so it's settable without having to recompile nim; a trivial change ... but ya, one more define (but a better one; it's prefixed) change defined(debug) to isDefined(conf, "nimDebug") in msgs.quit for debugging nim timotheecour/Nim#253 ; and if nim wasn't built with --stacktrace, it'd show a good errmsg: To create a stacktrace, rerun compilation with... as opposed to nothing like was the case here