Memory Leak with --gc:orc and Nimble Decimal Library

[rbohl64]

Hello,

I have a testcase cut down from a larger application that leaks memory with 
--gc:orc but does not leak memory with --gc:refc. The testcase uses the Decimal 
library from Nimble.

Are there steps that library providers need to take to support --gc:orc ? What 
should I investigate to determine if the issue is in the Decimal libarary or in 
the nim compiler ?

The testcase below leaks memory from the collect() macro when using nim v1.6.6 
(git hash 0565a70eab02122ce278b98181c7d1170870865c) on Ubuntu 18.0.4:
    
    
    
    import strutils, strformat
    import decimal/decimal
    import sugar
    
    type
      Timeval {.importc: "timeval", header:"<sys/time.h>", bycopy.} = object
      
      Rusage* {.importc: "struct rusage", header:"<sys/resource.h>", bycopy.} = 
object
        ru_utime {.importc.}: Timeval
        ru_stime {.importc.}: Timeval
        ru_maxrss* {.importc.}: int32  # Maximum resident set size
        # ...
        ru_minflt* {.importc.}: int32  # page reclaims (soft page faults)
      
      RusageWho* {.size: sizeof(cint).} = enum
        RusageChildren = -1
        RusageSelf = 0
        RusageThread = 1
    
    proc getrusage*(who: RusageWho, usage: var Rusage) {.importc, header: 
"sys/resource.h".}
    
    
    proc main() =
        
        let constDcm = newDecimal("0.15")
        var newRange = collect(for x in 0..<10000: constDcm + 1)
        
        var ru: Rusage
        getrusage(RusageSelf, ru)
        let initRss = ru.ru_maxrss
        var lastRss = initRss
        
        let prInterval = 100
        for i in 0..<1000:
            
            # Operation which leaks memory with --gc:orc,
            # but does not leak memoryy with --gc:refc
            # Note - need the add operation with
            # a Decimal in collect() below
            newRange = collect(for x in 0..<10000: constDcm + 1)
            
            # Attempt to reclaim memory
            GC_fullCollect()
            
            # Check memory consumption
            getrusage(RusageSelf, ru)
            if ru.ru_maxrss > 100 * initRss:
                raise newException(ValueError,"\n\n!!!!! Leaking Memory 
!!!!!\n\n")
            
            # Periodically print stats on memory consumption
            if  i mod prInterval == 0:
                echo &"\nGC_getStatistics():\n{GC_getStatistics()}"
                var incRss = ru.ru_maxrss - lastRss
                lastRss = ru.ru_maxrss
                echo &"Max RSS {ru.ru_maxrss}, Incremental max RSS: {incRss} 
for {prInterval} iterations"
                echo()
                
                when defined(nimTypeNames):
                    dumpNumberOfInstances()
                    echo()
        
        echo "\n\n###### No Memory Leak ######\n\n"
    
    when isMainModule:
        main()
    
    
    Run