Revert "Remove unused _pytest.code.Source.isparseable function"

This reverts commit c627ac4e59.

src/_pytest/_code/source.py

@@ -136,6 +136,26 @@ 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.
+        """
+        from parser import suite as syntax_checker
+
+        if deindent:
+            source = str(self.deindent())
+        else:
+            source = str(self)
+        try:
+            # compile(source+'\n', "x", "exec")
+            syntax_checker(source + "\n")
+        except KeyboardInterrupt:
+            raise
+        except Exception:
+            return False
+        else:
+            return True
+
     def __str__(self) -> str:
         return "\n".join(self.lines)