PEP 626: constant tests are kept as no-ops

The conditionals are now getting unwieldy, perhaps we can simplify them
in the future?

2 files changed, 24 insertions, 3 deletions

diff --git a/coverage/env.py b/coverage/env.py
index b91af463..e9c65bb1 100644
--- a/coverage/env.py
+++ b/coverage/env.py
@@ -33,14 +33,27 @@ PYPY3 = PYPY and PY3
 class PYBEHAVIOR(object):
     """Flags indicating this Python's behavior."""
 
+    pep626 = CPYTHON and (PYVERSION > (3, 10, 0, 'alpha', 4))
+
     # Is "if __debug__" optimized away?
-    optimize_if_debug = (not PYPY)
+    if PYPY3:
+        optimize_if_debug = True
+    elif PYPY2:
+        optimize_if_debug = False
+    else:
+        optimize_if_debug = not pep626
 
     # Is "if not __debug__" optimized away?
     optimize_if_not_debug = (not PYPY) and (PYVERSION >= (3, 7, 0, 'alpha', 4))
+    if pep626:
+        optimize_if_not_debug = False
+    if PYPY3:
+        optimize_if_not_debug = True
 
     # Is "if not __debug__" optimized away even better?
     optimize_if_not_debug2 = (not PYPY) and (PYVERSION >= (3, 8, 0, 'beta', 1))
+    if pep626:
+        optimize_if_not_debug2 = False
 
     # Do we have yield-from?
     yield_from = (PYVERSION >= (3, 3))
@@ -67,7 +80,7 @@ class PYBEHAVIOR(object):
     # used to be an empty string (meaning the current directory). It changed
     # to be the actual path to the current directory, so that os.chdir wouldn't
     # affect the outcome.
-    actual_syspath0_dash_m = (not PYPY) and (PYVERSION >= (3, 7, 0, 'beta', 3))
+    actual_syspath0_dash_m = CPYTHON and (PYVERSION >= (3, 7, 0, 'beta', 3))
 
     # When a break/continue/return statement in a try block jumps to a finally
     # block, does the finally block do the break/continue/return (pre-3.8), or
@@ -97,6 +110,9 @@ class PYBEHAVIOR(object):
     # real line of code.  Now they always start at 1.
     module_firstline_1 = pep626
 
+    # Are "if 0:" lines (and similar) kept in the compiled code?
+    keep_constant_test = pep626
+
 # Coverage.py specifics.
 
 # Are we using the C-implemented trace function?
diff --git a/coverage/parser.py b/coverage/parser.py
index 6a3ca2fc..1e307c41 100644
--- a/coverage/parser.py
+++ b/coverage/parser.py
@@ -1118,9 +1118,14 @@ class AstArcAnalyzer(object):
 
     @contract(returns='ArcStarts')
     def _handle__While(self, node):
-        constant_test = self.is_constant_expr(node.test)
         start = to_top = self.line_for_node(node.test)
+        constant_test = self.is_constant_expr(node.test)
+        top_is_body0 = False
         if constant_test and (env.PY3 or constant_test == "Num"):
+            top_is_body0 = True
+        if env.PYBEHAVIOR.keep_constant_test:
+            top_is_body0 = False
+        if top_is_body0:
             to_top = self.line_for_node(node.body[0])
         self.block_stack.append(LoopBlock(start=to_top))
         from_start = ArcStart(start, cause="the condition on line {lineno} was never true")