superdiff

Are you working to eliminate similar/duplicate code from your files? Do you have a suspicion that chunks of code are copy-pasted, but are slightly different s.t. normal diff methods don't work? Are you tired of visually going through and inspecting your code for repeating chunks?

If so, this might be the tool for you!

Features

• Finds duplicate code slices
• Finds similar-enough code slices
• JSON reporting for jq integeration
• Fast enough (00:03:39 for a 17k LOC with block size 10 and Levenshtein threshold 10)
• Can check for duplicate code across multiple files
• Vim integration!

Limitations

• Not instantaneous for large files
• Single-threaded

Usage

Say you have some file examples/really-bad-code.py that you want to inspect.

#!/usr/bin/env python

class SomeClass:
    def __init__(self):
        self.alpha = 12
        self.beta = 14
        self.gamma = 16
        self.is_bad = True

    def reset(self):
        self.alpha = 12
        self.beta = 14
        self.gamma = 16
        self.is_bad = True

    def do_something(self):
        d = {}

        import random
        for i in range(20):
            if i % 3 == 0: continue
            d[i] = random.randrange(1, 1001)
            d[i ** 2] = d[i] ** 2
            d[d[i]] = i

    def do_something_else(self):
        d = {}

        import random
        for i in range(21):
            if i % 3 == 1: continue
            d[i] = random.randrange(1, 1001)
            d[i ** 2] = d[i]
            d[d[i]] = i

inst = SomeClass()
inst.reset()

You have a feeling that it might be bad, so you use the tool.

$ superdiff -b 4 examples/really-bad-code.py
1 file(s) ["examples/really-bad-code.py"]
Verbosity (-v): true
Comparison threshold (-t): 0 (Strict equality)
Minimum length of first line before block consideration (-l): 1
Minimum length of block before consideration (-b): 4
Now comparing "examples/really-bad-code.py" (   37/   38)...done 1 out of 1
=== MATCH ===
File: "examples/really-bad-code.py"
Lines: [4, 10]
Size: 5

A total of 1 unique match(es) were found in the 1 file(s).

Wow! That's pretty nice that you found that! But maybe there are places in the file that aren't exact copies, but are similar enough.

$ superdiff -b 4 -t 5 examples/really-bad-code.py
1 file(s) ["examples/really-bad-code.py"]
Verbosity (-v): true
Comparison threshold (-t): 5 (Levenshtein distance)
Minimum length of first line before block consideration (-l): 1
Minimum length of block before consideration (-b): 4
Now comparing "examples/really-bad-code.py" (   37/   38)...done 1 out of 1
=== MATCH ===
File: "examples/really-bad-code.py"
Lines: [15, 25]
Size: 10

=== MATCH ===
File: "examples/really-bad-code.py"
Lines: [4, 10]
Size: 5

A total of 2 unique match(es) were found in the 1 file(s).

Huh, apparently there is a duplicate function that are pretty similar! And now (assuming that the output of the function is pretty long and not laughably short), you want to know if line 30 is involved in duplicate code, so you do the following:

$ superdiff --reporting-mode json -b 5 -t 5 examples/really-bad-code.py > output.json
$ cat output.json | jq
[
  [
    {
      "file": "examples/really-bad-code.py",
      "line": 5,
      "size": 5
    },
    {
      "file": "examples/really-bad-code.py",
      "line": 11,
      "size": 5
    }
  ],
  [
    {
      "file": "examples/really-bad-code.py",
      "line": 16,
      "size": 10
    },
    {
      "file": "examples/really-bad-code.py",
      "line": 26,
      "size": 10
    }
  ]
]
$ cat output.json | jq 'map(select((. | any(.line <= 30)) and (.[0].size as $length | . | any(.line + $length > 30))))'
[
  [
    {
      "file": "examples/really-bad-code.py",
      "line": 16,
      "size": 10
    },
    {
      "file": "examples/really-bad-code.py",
      "line": 26,
      "size": 10
    }
  ]
]

Note: If anyone finds a better way of making the jq query, please make a pull request and/or let me know.

In the works

• Interactive HTML reports from generated JSON