isort range formatting deletes lines

[stevearc]

          I'm having an issue with lines being removed due to `isort`, probably related.

Test file:

import numpy as np

from A import B
import C

Output if I use conform.format() (works as expected):

import C
import numpy as np
from A import B

Output if I use conform.format({range = {start={1, 0}, ["end"]={4,8}}}) (whole file as range):

import C

I tracked it down to apply_format, in particular indices_in_range here is evaluating to false, so it does the deletion but not the insertion, shown in the lack of a second text edit for the call with a range. If I bypass that line (just saying if true for this test), it works exactly as expected.

trace for no range (conform.format()):

15:06:37[DEBUG] Running formatters on ~/test.py: { "isort" }
15:06:37[INFO] Run isort on ~/test.py
15:06:37[TRACE] Input lines: { "import numpy as np", "", "from A import B", "import C" }
15:06:37[DEBUG] Run command: { "isort", "--stdout", "--filename", "~/test.py", "-" }
15:06:38[DEBUG] isort exited with code 0
15:06:38[TRACE] Output lines: { "import C", "import numpy as np", "from A import B" }
15:06:38[TRACE] Applying formatting to ~/test.py
15:06:38[TRACE] Comparing lines { "import numpy as np", "", "from A import B", "import C" } and { "import C", "import numpy as np", "from A import B" }
15:06:38[TRACE] Diff indices { { 1, 3, 0, 0 }, { 4, 0, 2, 2 } }
15:06:38[TRACE] Applying text edits: { {
    newText = "",
    range = {
      ["end"] = {
        character = 0,
        line = 3
      },
      start = {
        character = 0,
        line = 0
      }
    }
  }, {
    newText = "import numpy as np\nfrom A import B",
    range = {
      ["end"] = {
        character = 0,
        line = 4
      },
      start = {
        character = 0,
        line = 4
      }
    }
  } }
15:06:38[TRACE] Done formatting ~/test.py

trace with a range (conform.format({range = {start={1, 0}, ["end"]={4,8}}})):

15:06:33[DEBUG] Running formatters on ~/test.py: { "isort" }
15:06:33[INFO] Run isort on ~/test.py
15:06:33[TRACE] Input lines: { "import numpy as np", "", "from A import B", "import C" }
15:06:33[DEBUG] Run command: { "isort", "--stdout", "--filename", "~/test.py", "-" }
15:06:33[DEBUG] isort exited with code 0
15:06:33[TRACE] Output lines: { "import C", "import numpy as np", "from A import B" }
15:06:33[TRACE] Applying formatting to ~/test.py
15:06:33[TRACE] Comparing lines { "import numpy as np", "", "from A import B", "import C" } and { "import C", "import numpy as np", "from A import B" }
15:06:33[TRACE] Diff indices { { 1, 3, 0, 0 }, { 4, 0, 2, 2 } }
15:06:33[TRACE] Applying text edits: { {
    newText = "",
    range = {
      ["end"] = {
        character = 0,
        line = 3
      },
      start = {
        character = 0,
        line = 0
      }
    }
  } }
15:06:33[TRACE] Done formatting ~/test.py

Originally posted by @milisims in #98 (comment)

[stevearc]

This is likely not related to the other issue, so I've moved it to a new issue.

I added some docs under advanced topics that explain the range formatting a little more. As a general rule, the "aftermarket" range formatting that conform offers when a formatter doesn't support it natively is a "best effort" operation and will never be perfect. In this particular case I was able to find a small change that improves the formatting results, but just as a warning this sort of thing can still happen in the future.