Some limited support for 3.8 "=" specifier

test/simple_source/bug38/02_fstring_debug.py

@@ -0,0 +1,32 @@
+# Tests new "debug" format new in 3.8.
+# Much of this is adapted from 3.8 test/test_fstring.py
+# RUNNABLE!
+
+"""This program is self-checking!"""
+
+# fmt: off
+# We want to use "=" and ":=" *without* the surrounding space to test format spec and "=" detection
+f'{f"{3.1415=:.1f}":*^20}' == '*****3.1415=3.1*****'
+
+y = 2
+def f(x, width):
+    return f'x={x*y:{width}}'
+
+assert f('foo', 10) ==  'x=foofoo    '
+
+x = 'bar'
+assert f(10, 10), 'x=        20'
+
+x = 'A string'
+f"x={x!r}" == 'x=' + repr(x)
+
+pi = 'π'
+assert f'alpha α {pi=} ω omega', "alpha α pi='π' ω omega"
+
+x = 20
+# This isn't an assignment expression, it's 'x', with a format
+# spec of '=10'.
+assert f'{x:=10}' ==  '        20'
+
+assert f'{(x:=10)}' ==  '10'
+assert x ==  10