Remove the trailing comma if there is only one argument to a call

This makes it consistent with removing the trailing comma when multiple
arguments to a call fit in a single line. It also makes it a tiny bit more
likely that an expression will fit a line that didn't use to.

README.md

@@ -260,6 +260,11 @@ More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
 
 ### 18.3a2 (unreleased)
 
+* ignore empty bracket pairs while splitting. This avoids very weirdly
+  looking formattings (#34, #35)
+
+* remove a trailing comma if there is a single argument to a call
+
 * fixed missing space in numpy-style array indexing (#33)
 
 * fixed spurious space after star-based unary expressions (#31)

black.py

@@ -508,6 +508,10 @@ def maybe_remove_trailing_comma(self, closing: Leaf) -> bool:
             bracket_depth = leaf.bracket_depth
             if bracket_depth == depth and leaf.type == token.COMMA:
                 commas += 1
+                if leaf.parent and leaf.parent.type == syms.arglist:
+                    commas += 1
+                    break
+
         if commas > 1:
             self.leaves.pop()
             return True
@@ -1480,7 +1484,7 @@ def _v(node: ast.AST, depth: int = 0) -> Iterator[str]:
         raise AssertionError(
             f"INTERNAL ERROR: Black produced invalid code: {exc}. "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
-            f"This invalid output might be helpful: {log}",
+            f"This invalid output might be helpful: {log}"
         ) from None
 
     src_ast_str = '\n'.join(_v(src_ast))
@@ -1491,7 +1495,7 @@ def _v(node: ast.AST, depth: int = 0) -> Iterator[str]:
             f"INTERNAL ERROR: Black produced code that is not equivalent to "
             f"the source.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
-            f"This diff might be helpful: {log}",
+            f"This diff might be helpful: {log}"
         ) from None
 
 
@@ -1510,7 +1514,7 @@ def assert_stable(src: str, dst: str, line_length: int) -> None:
             f"INTERNAL ERROR: Black produced different code on the second pass "
             f"of the formatter.  "
             f"Please report a bug on https://github.com/ambv/black/issues.  "
-            f"This diff might be helpful: {log}",
+            f"This diff might be helpful: {log}"
         ) from None
 
 

tests/expression.py

@@ -106,15 +106,15 @@
 b = 1,
 c = 1
 d = (1,) + a + (2,)
+e = (1,).count(1)
 what_is_up_with_those_new_coord_names = (coord_names + set(vars_to_create)) + set(vars_to_remove)
 what_is_up_with_those_new_coord_names = (coord_names | set(vars_to_create)) - set(vars_to_remove)
-
+result = session.query(models.Customer.id).filter(models.Customer.account_id == account_id, models.Customer.email == email_address).order_by(models.Customer.id.asc(),).all()
 
 def gen():
     yield from outside_of_generator
     a = (yield)
 
-
 async def f():
     await some.complicated[0].call(with_args=(True or (1 is not 1)))
 
@@ -239,12 +239,18 @@ async def f():
 b = 1,
 c = 1
 d = (1,) + a + (2,)
+e = (1,).count(1)
 what_is_up_with_those_new_coord_names = (coord_names + set(vars_to_create)) + set(
     vars_to_remove
 )
 what_is_up_with_those_new_coord_names = (coord_names | set(vars_to_create)) - set(
     vars_to_remove
 )
+result = session.query(models.Customer.id).filter(
+    models.Customer.account_id == account_id, models.Customer.email == email_address
+).order_by(
+    models.Customer.id.asc()
+).all()
 
 
 def gen():

tests/function.py

@@ -37,7 +37,7 @@ def example(session):
         models.Customer.account_id == account_id,
         models.Customer.email == email_address,
     ).order_by(
-        models.Customer.id.asc(),
+        models.Customer.id.asc()
     ).all()
 def long_lines():
     if True:
@@ -129,7 +129,7 @@ def example(session):
     result = session.query(models.Customer.id).filter(
         models.Customer.account_id == account_id, models.Customer.email == email_address
     ).order_by(
-        models.Customer.id.asc(),
+        models.Customer.id.asc()
     ).all()