Support for PEP492 async quasi-keyword in python.el

[Lele Gaifax]

Hi all,

I spent the afternoon teaching python.el to properly indent the new “async”
constructs introduced in Python 3.5, and I'm attaching the result of my
attempt. 

Of course it's far from being either correct or complete, but maybe some of
you could give me some feedback on the following points:

a) is there a better way to introduce the new "async" variants of
   "def|with|for" in the `block-start' regexp?

b) how should the "await" quasi-keyword be handled? I mean, it's not a real
   keyword (that is, the assignment “await = 1” is valid code for example),
   but in an expression such as “return await foo()” it should probably be
   highlighted as such...

c) the diff below breaks one existing test, namely `python-indent-region-5'; I
   will try to understand what's going on...

Thank you in advance for any hint,
ciao, lele.

diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index 6ff12b5..9f5c087 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -384,7 +384,10 @@ python-mode-map
   (defconst python-rx-constituents
     `((block-start          . ,(rx symbol-start
                                    (or "def" "class" "if" "elif" "else" "try"
-                                       "except" "finally" "for" "while" "with")
+                                       "except" "finally" "for" "while" "with"
+                                       ;; Python 3.5+ PEP492
+                                       (and "async" (+ space)
+                                            (or "def" "for" "with")))
                                    symbol-end))
       (dedenter            . ,(rx symbol-start
                                    (or "elif" "else" "except" "finally")
@@ -395,7 +398,11 @@ python-mode-map
                                   symbol-end))
       (decorator            . ,(rx line-start (* space) ?@ (any letter ?_)
                                    (* (any word ?_))))
-      (defun                . ,(rx symbol-start (or "def" "class") symbol-end))
+      (defun                . ,(rx symbol-start
+                                   (or "def" "class"
+                                       ;; Python 3.5+ PEP492
+                                       (and "async" (+ space) "def"))
+                                   symbol-end))
       (if-name-main         . ,(rx line-start "if" (+ space) "__name__"
                                    (+ space) "==" (+ space)
                                    (any ?' ?\") "__main__" (any ?' ?\")
@@ -527,6 +534,8 @@ python-font-lock-keywords
           ;; fontified like that in order to keep font-lock consistent between
           ;; Python versions.
           "nonlocal"
+          ;; Python 3.5+ PEP492
+          (and "async" (+ space) (or "def" "for" "with"))
           ;; Extra:
           "self")
          symbol-end)
diff --git a/test/automated/python-tests.el b/test/automated/python-tests.el
index 44b05e2..23d799a 100644
--- a/test/automated/python-tests.el
+++ b/test/automated/python-tests.el
@@ -604,6 +604,42 @@ python-tests-visible-string
    (should (eq (car (python-indent-context)) :after-line))
    (should (= (python-indent-calculate-indentation) 0))))
 
+(ert-deftest python-indent-after-async-block-1 ()
+  "Test PEP492 async def."
+  (python-tests-with-temp-buffer
+   "
+async def foo(a, b, c=True):
+"
+   (should (eq (car (python-indent-context)) :no-indent))
+   (should (= (python-indent-calculate-indentation) 0))
+   (goto-char (point-max))
+   (should (eq (car (python-indent-context)) :after-block-start))
+   (should (= (python-indent-calculate-indentation) 4))))
+
+(ert-deftest python-indent-after-async-block-2 ()
+  "Test PEP492 async with."
+  (python-tests-with-temp-buffer
+   "
+async with foo(a) as mgr:
+"
+   (should (eq (car (python-indent-context)) :no-indent))
+   (should (= (python-indent-calculate-indentation) 0))
+   (goto-char (point-max))
+   (should (eq (car (python-indent-context)) :after-block-start))
+   (should (= (python-indent-calculate-indentation) 4))))
+
+(ert-deftest python-indent-after-async-block-3 ()
+  "Test PEP492 async for."
+  (python-tests-with-temp-buffer
+   "
+async for a in sequencer():
+"
+   (should (eq (car (python-indent-context)) :no-indent))
+   (should (= (python-indent-calculate-indentation) 0))
+   (goto-char (point-max))
+   (should (eq (car (python-indent-context)) :after-block-start))
+   (should (= (python-indent-calculate-indentation) 4))))
+
 (ert-deftest python-indent-after-backslash-1 ()
   "The most common case."
   (python-tests-with-temp-buffer
@@ -1483,6 +1519,26 @@ python-tests-visible-string
                 (beginning-of-line)
                 (point))))))
 
+(ert-deftest python-nav-beginning-of-defun-3 ()
+  (python-tests-with-temp-buffer
+   "
+class C(object):
+
+    async def m(self):
+        return await self.c()
+
+    async def c(self):
+        pass
+"
+   (python-tests-look-at "self.c()")
+   (should (= (save-excursion
+                (python-nav-beginning-of-defun)
+                (point))
+              (save-excursion
+                (python-tests-look-at "async def m" -1)
+                (beginning-of-line)
+                (point))))))
+
 (ert-deftest python-nav-end-of-defun-1 ()
   (python-tests-with-temp-buffer
    "

-- 
nickname: Lele Gaifax | Quando vivrò di quello che ho pensato ieri
real: Emanuele Gaifas | comincerò ad aver paura di chi mi copia.
address@hidden  |                 -- Fortunato Depero, 1929.