Remove usage of parser module (deprecated in Python 3.9) (#6407)

Remove usage of parser module (deprecated in Python 3.9)

changelog/6404.trivial.rst

@@ -1 +1 @@
-Removed unused ``_pytest.code.Source.isparseable`` function.
+Remove usage of ``parser`` module, deprecated in Python 3.9.

src/_pytest/_code/source.py

@@ -136,6 +136,21 @@ class Source:
         newsource.lines[:] = deindent(self.lines)
         return newsource
 
+    def isparseable(self, deindent: bool = True) -> bool:
+        """ return True if source is parseable, heuristically
+            deindenting it by default.
+        """
+        if deindent:
+            source = str(self.deindent())
+        else:
+            source = str(self)
+        try:
+            ast.parse(source)
+        except (SyntaxError, ValueError, TypeError):
+            return False
+        else:
+            return True
+
     def __str__(self) -> str:
         return "\n".join(self.lines)
 

testing/code/test_source.py

@@ -121,6 +121,15 @@ def test_syntaxerror_rerepresentation() -> None:
     assert ex.value.text == "xyz xyz\n"
 
 
+def test_isparseable() -> None:
+    assert Source("hello").isparseable()
+    assert Source("if 1:\n  pass").isparseable()
+    assert Source(" \nif 1:\n  pass").isparseable()
+    assert not Source("if 1:\n").isparseable()
+    assert not Source(" \nif 1:\npass").isparseable()
+    assert not Source(chr(0)).isparseable()
+
+
 class TestAccesses:
     def setup_class(self) -> None:
         self.source = Source(
@@ -134,6 +143,7 @@ class TestAccesses:
 
     def test_getrange(self) -> None:
         x = self.source[0:2]
+        assert x.isparseable()
         assert len(x.lines) == 2
         assert str(x) == "def f(x):\n    pass"