magic trailing comma not working in certain scenario

[nipunn1313]

Describe the bug

Trailing commas are incorrectly being ruthlessly collapsed into one line

To Reproduce

Reproes in the black playground

def method(
    self,
) -> typing_extensions.Literal[
    "l1",
    "l2",
]: pass

Result is

def method(
    self,
) -> typing_extensions.Literal["l1", "l2",]:
    pass

Expected behavior

I'd expect no change to the Literal writeout.

Environment

Black 22.6.0 in the black playground.

Additional context

I noticed that if we eliminate the self argument, then black works correctly. Seems to have something to do with the fact that there are two trailing command in the method definition. Second one is not respected.

[hauntsaninja]

I believe I've fixed this on main (you'll need to remember to use --preview because it's a change that changed formatting)

[nipunn1313]

at least according to https://black.vercel.app/?version=main&state=_Td6WFoAAATm1rRGAgAhARYAAAB0L-Wj4AC-AINdAD2IimZxl1N_WlbvK5V-fxcIRXBgNMb3PFjqcfxrMLJktSq6aRkCvRw96aIv09NBV5YAN_i6LoE0TXjAbbQNrVw7f1j0gc081LNWKW-py5In4PDB2yLCB7g7UtBGcgpzfVSuBjKXeq0n0j_UCcVdPayPJYNVCTnoYOpOVSTXbdZaNMEqAABhxmDJI41ybQABnwG_AQAAAG3WVrHEZ_sCAAAAAARZWg== - it doesn't seem fixed

I checked the box that claims to use --preview

[JelleZijlstra]

Yes, not fixed yet:

$ black --diff --preview tryit.py 
--- tryit.py    2022-09-02 02:02:08.120028 +0000
+++ tryit.py    2022-09-02 02:02:16.343920 +0000
@@ -1,6 +1,4 @@
 def method(
     self,
-) -> typing_extensions.Literal[
-    "l1",
-    "l2",
-]: pass
+) -> typing_extensions.Literal["l1", "l2",]:
+    pass
would reformat tryit.py

All done! ✨ 🍰 ✨
1 file would be reformatted.
$ black --version
black, 22.8.0 (compiled: yes)
Python (CPython) 3.9.12

(22.8.0 is the same as main right now)

[hauntsaninja]

@nipunn1313 your playground link does not check the box that says "Don't use trailing commas as a reason to split lines."
@JelleZijlstra you didn't pass --skip-magic-trailing-comma

~/dev/black main λ black --diff --preview x.py -C
--- x.py	2022-09-02 02:06:01.742586 +0000
+++ x.py	2022-09-02 02:07:53.238628 +0000
@@ -1,6 +1,2 @@
-def method(
-    self,
-) -> typing_extensions.Literal[
-    "l1",
-    "l2",
-]: pass
+def method(self) -> typing_extensions.Literal["l1", "l2"]:
+    pass
would reformat x.py

All done! ✨ 🍰 ✨
1 file would be reformatted.

[nipunn1313]

I want the default behavior of the magic trailing comma!

It appears that the magic trailing comma's behavior is not being respected in this case.

[hauntsaninja]

Okay, sure. Your issue title skip_magic_trailing_comma=true seems incorrect then?

Note that this was a trailing comma that wasn't removed with --skip-magic-trailing-comma until #3209, hence my claim in #3239 (comment)

[nipunn1313]

OOPS. I totally inverted my statement in the title of the task! Booleans are hard.
Editing title

[hauntsaninja]

I think your example is basically a duplicate of #2498 which was closed as a duplicate of #1671 although the issue title of #1671 doesn't quite apply to your case / #2498

[JelleZijlstra]

Yeah I think this is basically #1671.