gh-98931: Add custom error messages to invalid import/from with multiple targets (#105985)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Grammar/python.gram

@@ -1293,7 +1293,7 @@ invalid_group:
     | '(' a='**' expression ')' {
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "cannot use double starred expression here") }
 invalid_import:
-    | a='import' dotted_name 'from' dotted_name {
+    | a='import' ','.dotted_name+ 'from' dotted_name {
         RAISE_SYNTAX_ERROR_STARTING_FROM(a, "Did you mean to use 'from ... import ...' instead?") }
 
 invalid_import_from_targets:

Lib/test/test_syntax.py

@@ -1621,6 +1621,22 @@
 Traceback (most recent call last):
 SyntaxError: Did you mean to use 'from ... import ...' instead?
 
+>>> import a, b,c from b
+Traceback (most recent call last):
+SyntaxError: Did you mean to use 'from ... import ...' instead?
+
+>>> import a.y.z, b.y.z, c.y.z from b.y.z
+Traceback (most recent call last):
+SyntaxError: Did you mean to use 'from ... import ...' instead?
+
+>>> import a,b,c from b as bar
+Traceback (most recent call last):
+SyntaxError: Did you mean to use 'from ... import ...' instead?
+
+>>> import a.y.z, b.y.z, c.y.z from b.y.z as bar
+Traceback (most recent call last):
+SyntaxError: Did you mean to use 'from ... import ...' instead?
+
 # Check that we dont raise the "trailing comma" error if there is more
 # input to the left of the valid part that we parsed.
 

Misc/NEWS.d/next/Core and Builtins/2023-06-22-14-19-17.gh-issue-98931.PPgvSF.rst

@@ -0,0 +1,2 @@
+Ensure custom :exc:`SyntaxError` error messages are raised for invalid
+imports with multiple targets. Patch by Pablo Galindo