[Python] Add support for some new syntax in Python 3.8 (sublimehq#2006)

* [Python] Support `=` debug indicator in f-strings

New in Python 3.8.
Upstream change: python/cpython@9a4135e

* [Python] Support "positional args only" operator

Added in Python 3.8 via https://www.python.org/dev/peps/pep-0570/.

Python/Python.sublime-syntax

@@ -626,6 +626,13 @@ contexts:
     - match: ','
       scope: punctuation.separator.parameters.python
       push: allow-unpack-operators
+    - match: /
+      scope: storage.modifier.positional-args-only.python
+      push:
+        - match: (?=[,)])
+          pop: true
+        - match: \S
+          scope: invalid.illegal.expected-comma.python
     - match: '(?==)'
       set:
         - match: '='
@@ -1426,6 +1433,8 @@ contexts:
           pop: true
         - match: '![ars]'
           scope: storage.modifier.conversion.python
+        - match: =
+          scope: storage.modifier.debug.python
         - match: ':'
           push:
             - meta_scope: meta.format-spec.python constant.other.format-spec.python
@@ -1438,7 +1447,7 @@ contexts:
         - match: ''
           push:
             - meta_content_scope: source.python.embedded
-            - match: (?=![^=]|:|\})
+            - match: (?==?(![^=]|:|\}))
               pop: true
             - match: \\
               scope: invalid.illegal.backslash-in-fstring.python

Python/syntax_test_python.py

@@ -729,6 +729,15 @@ def foo(arg: int = 0, (x: float, y=20) = (0.0, "default")):
 #                                                       ^ punctuation.section.sequence.end.python
     pass
 
+def name(p1, p2=None, /, p_or_kw=None, *, kw): pass
+#                     ^ storage.modifier.positional-args-only.python
+#                      ^ punctuation.separator.parameters.python
+#                                      ^ keyword.operator.unpacking.sequence.python
+def name(p1, p2, /): pass
+#                ^ storage.modifier.positional-args-only.python
+#                 ^ punctuation.section.parameters.end.python
+
+
 ##################
 # Class definitions
 ##################

Python/syntax_test_python_strings.py

@@ -646,6 +646,33 @@
 #           ^ invalid.illegal.stray-brace
 """
 
+# Most of these were inspired by
+# https://github.com/python/cpython/commit/9a4135e939bc223f592045a38e0f927ba170da32
+f'{x=:}'
+#   ^ storage.modifier.debug.python
+f'{x=:.2f}'
+#   ^ storage.modifier.debug.python
+f'{x=!r}'
+#   ^ storage.modifier.debug.python
+f'{x=!a}'
+#   ^ storage.modifier.debug.python
+f'{x=!s:*^20}'
+#   ^ storage.modifier.debug.python
+#    ^^ storage.modifier.conversion.python
+#      ^^^^^ meta.format-spec.python
+f'{"Σ"=}'
+#     ^ storage.modifier.debug.python
+f'{0==1}'
+#   ^^ -storage.modifier.debug.python
+f'{0!=1}'
+#    ^ -storage.modifier.debug.python
+f'{0<=1}'
+#    ^ -storage.modifier.debug.python
+f'{0>=1}'
+#    ^ -storage.modifier.debug.python
+f'{f(a="3=")}'
+#     ^^^^ -storage.modifier.debug.python
+
 f" {
 %   ^ invalid.illegal.unclosed-string
    # TODO make this test pass