mort

A dead code branch locator for Nim. This library will find places in your code that contain dead branches that are not executed at runtime. Nim already has dead code elimination at compile time but this won't, for example, eliminate a dead branch on your if else statement, because that can only be determined at run time.

Say you have a Nim module like so:

proc notUsedProc() =
  echo "being optimized"
  
proc main() =
  let input = stdin.readLine()
  if input == "hello":
    echo "Hi!"
  else:
    echo "You're supposed to greet me"

main()

You can see by the above code that the notUsedProc() can be optimized away at compile time, but the if/else statement depends on user input and cannot be optimized away.

But maybe you have a bug in the if input == "hello" branch but that never gets called very often or at all. This library can tell you (based on runtime usage) whether or not your branches get called and let you know. This could be useful for test coverage for example.

Usage

Simply use the findDeadCode macro on your code, shown below, then call either or both of printCodeUsage or printDeadCode. Or you can get the usage table itself to do with what you like via getUsageTable, which returns a TableRef[string, TableRef[int, int]] where the string is the filename and the inner table has key = lineNumber and value = timesCalled.

import mort

findDeadCode:
  # ... insert Nim code here
  discard

# OR

proc myNimProc() {.findDeadCode.} =
  # .. insert Nim code here
  discard
  
  
proc main() =
  # Call your proc/code that you want to be logged
  myNimProc()
  
  # then call ``printCodeUsage`` and/or ``printDeadCode``
  printCodeUsage()
  printDeadCode()
  
  # or get the information yourself:
  let usageTable: TableRef[string, TableRef[int, int]] = getUsageTable()
  # Do cool stuff, like get test coverage

main()

Then compile your code with the -d:findDeadCode compiler flag to enable finding dead code.

Example usage

nim c -r -d:findDeadCode tests/testmort.nim

Output:

6: 2
8: 1
10: 20
11: 0
13: 4
18: 16
22: 2
25: 0

Dead code found in /Users/joey/Projects/mort/tests/testmort.nim
at line 11

Dead code found in /Users/joey/Projects/mort/tests/testmort.nim
at line 25