Fix python-shell-buffer-substring when retrieving a single statement

* lisp/progmodes/python.el (python-shell-buffer-substring): Do not add
"if True:" line when retrieving a single statement.
(python-shell-send-region): Add a reference to
`python-shell-buffer-substring' in docstring.
* test/lisp/progmodes/python-tests.el (python-shell-buffer-substring-13)
(python-shell-buffer-substring-14, python-shell-buffer-substring-15)
(python-shell-buffer-substring-16, python-shell-buffer-substring-17):
New tests. (Bug#60142)

lisp/progmodes/python.el

@@ -3736,19 +3736,35 @@ the python shell:
      appending extra empty lines so tracebacks are correct.
   3. When the region sent is a substring of the current buffer, a
      coding cookie is added.
-  4. Wraps indented regions under an \"if True:\" block so the
+  4. When the region consists of a single statement, leading
-     interpreter evaluates them correctly."
+     whitespaces will be removed.  Otherwise, wraps indented
-  (let* ((start (save-excursion
+     regions under an \"if True:\" block so the interpreter
-                  ;; If we're at the start of the expression, and
+     evaluates them correctly."
-                  ;; there's just blank space ahead of it, then expand
+  (let* ((single-p (save-restriction
-                  ;; the region to include the start of the line.
+                     (narrow-to-region start end)
-                  ;; This makes things work better with the rest of
+                     (= (progn
-                  ;; the data we're sending over.
                           (goto-char start)
+                          (python-nav-beginning-of-statement))
+                        (progn
+                          (goto-char end)
+                          (python-nav-beginning-of-statement)))))
+         (start (save-excursion
+                  ;; If we're at the start of the expression, and if
+                  ;; the region consists of a single statement, then
+                  ;; remove leading whitespaces, else if there's just
+                  ;; blank space ahead of it, then expand the region
+                  ;; to include the start of the line.  This makes
+                  ;; things work better with the rest of the data
+                  ;; we're sending over.
+                  (goto-char start)
+                  (if single-p
+                      (progn
+                        (skip-chars-forward "[:space:]" end)
+                        (point))
                     (if (string-blank-p
                          (buffer-substring (line-beginning-position) start))
                         (line-beginning-position)
-                    start)))
+                      start))))
          (substring (buffer-substring-no-properties start end))
          (starts-at-point-min-p (save-restriction
                                   (widen)
@@ -3772,7 +3788,7 @@ the python shell:
       (python-mode)
       (when fillstr
         (insert fillstr))
-      (when (not toplevel-p)
+      (when (and (not single-p) (not toplevel-p))
         (forward-line -1)
         (insert "if True:\n")
         (delete-region (point) (line-end-position)))
@@ -3816,7 +3832,8 @@ code inside blocks delimited by \"if __name__== \\='__main__\\=':\".
 When called interactively SEND-MAIN defaults to nil, unless it's
 called with prefix argument.  When optional argument MSG is
 non-nil, forces display of a user-friendly message if there's no
-process running; defaults to t when called interactively."
+process running; defaults to t when called interactively.  The
+substring to be sent is retrieved using `python-shell-buffer-substring'."
   (interactive
    (list (region-beginning) (region-end) current-prefix-arg t))
   (let* ((string (python-shell-buffer-substring start end (not send-main)

test/lisp/progmodes/python-tests.el

@@ -4456,6 +4456,70 @@ def foo():
                      (point-max))
                     "# -*- coding: utf-8 -*-\n\nif True:\n        # Whitespace\n\n    print ('a')\n\n"))))
 
+(ert-deftest python-shell-buffer-substring-13 ()
+  "Check substring from indented single statement."
+  (python-tests-with-temp-buffer
+   "
+def foo():
+    a = 1
+"
+   (should (string= (python-shell-buffer-substring
+                     (python-tests-look-at "a = 1")
+                     (pos-eol))
+                    "# -*- coding: utf-8 -*-\n\na = 1"))))
+
+(ert-deftest python-shell-buffer-substring-14 ()
+  "Check substring from indented single statement spanning multiple lines."
+  (python-tests-with-temp-buffer
+   "
+def foo():
+    a = \"\"\"Some
+    string\"\"\"
+"
+   (should (string= (python-shell-buffer-substring
+                     (python-tests-look-at "a = \"\"\"Some")
+                     (pos-eol 2))
+                    "# -*- coding: utf-8 -*-\n\na = \"\"\"Some\n    string\"\"\""))))
+
+(ert-deftest python-shell-buffer-substring-15 ()
+  "Check substring from partial statement."
+  (python-tests-with-temp-buffer
+   "
+def foo():
+    a = 1
+"
+   (should (string= (python-shell-buffer-substring
+                     (python-tests-look-at "    a = 1")
+                     (python-tests-look-at " = 1"))
+                    "# -*- coding: utf-8 -*-\n\na"))))
+
+(ert-deftest python-shell-buffer-substring-16 ()
+  "Check substring from partial statement."
+  (python-tests-with-temp-buffer
+   "
+def foo():
+    a = 1
+"
+   (should (string= (python-shell-buffer-substring
+                     (python-tests-look-at "1")
+                     (1+ (point)))
+                    "# -*- coding: utf-8 -*-\n\n1"))))
+
+(ert-deftest python-shell-buffer-substring-17 ()
+  "Check substring from multiline string."
+  (python-tests-with-temp-buffer
+   "
+def foo():
+    s = \"\"\"
+    a = 1
+    b = 2
+\"\"\"
+"
+   (should (string= (python-shell-buffer-substring
+                     (python-tests-look-at "a = 1")
+                     (python-tests-look-at "\"\"\""))
+                    "# -*- coding: utf-8 -*-\n\nif True:\n    a = 1\n    b = 2\n\n"))))
+
 
 
 ;;; Shell completion