Fix unstable formatting on string split + % formatting (#1680)

Fixes #1595

src/black/__init__.py

@@ -2668,9 +2668,9 @@ def rhs(line: Line, features: Collection[Feature]) -> Iterator[Line]:
                 transformers = [
                     string_merge,
                     string_paren_strip,
+                    string_split,
                     delimiter_split,
                     standalone_comment_split,
-                    string_split,
                     string_paren_wrap,
                     rhs,
                 ]

src/blib2to3/pgen2/pgen.py

@@ -168,8 +168,7 @@ def calcfirst(self, name: Text) -> None:
                 if symbol in inverse:
                     raise ValueError(
                         "rule %s is ambiguous; %s is in the first sets of %s as well"
-                        " as %s"
+                        " as %s" % (name, symbol, label, inverse[symbol])
-                        % (name, symbol, label, inverse[symbol])
                     )
                 inverse[symbol] = label
         self.first[name] = totalset

tests/data/long_strings.py

@@ -380,8 +380,7 @@ def foo():
 
 old_fmt_string1 = (
     "While we are on the topic of %s, we should also note that old-style formatting"
-    " must also be preserved, since some %s still uses it."
+    " must also be preserved, since some %s still uses it." % ("formatting", "code")
-    % ("formatting", "code")
 )
 
 old_fmt_string2 = "This is a %s %s %s %s" % (
@@ -448,8 +447,7 @@ def foo():
 
 assert some_type_of_boolean_expression, (
     "Followed by a really really really long string that is used to provide context to"
-    " the AssertionError exception, which uses dynamic string %s."
+    " the AssertionError exception, which uses dynamic string %s." % "formatting"
-    % "formatting"
 )
 
 assert some_type_of_boolean_expression, (

tests/data/long_strings__regression.py

@@ -310,6 +310,13 @@ def who(self):
             passenger_association=passenger_association,
         )
 
+if __name__ == "__main__":
+    for i in range(4, 8):
+        cmd = (
+            r"for pid in $(ps aux | grep paster | grep -v grep | grep '\-%d' | awk '{print $2}'); do kill $pid; done"
+            % (i)
+        )
+
 # output
 
 
@@ -435,14 +442,12 @@ def foo():
 
 func_call_where_string_arg_has_old_fmt_and_bad_parens(
     "A long string with {}. This string is so long that it is ridiculous. It can't fit"
-    " on one line at alllll."
+    " on one line at alllll." % "formatting",
-    % "formatting",
 )
 
 func_call_where_string_arg_has_old_fmt_and_bad_parens(
     "A long string with {}. This {} is so long that it is ridiculous. It can't fit on"
-    " one line at alllll."
+    " one line at alllll." % ("formatting", "string"),
-    % ("formatting", "string"),
 )
 
 
@@ -702,3 +707,11 @@ def who(self):
                 passenger_association=passenger_association,
             )
         )
+
+
+if __name__ == "__main__":
+    for i in range(4, 8):
+        cmd = (
+            r"for pid in $(ps aux | grep paster | grep -v grep | grep '\-%d' | awk"
+            r" '{print $2}'); do kill $pid; done" % (i)
+        )