fix(extract): raise RefactoringError for empty or whitespace-only region

CHANGELOG.md

@@ -3,6 +3,7 @@
 - #895 patchedast Starred and keyword now consumes their syntactically expected and ** (@lieryan)
 - #896 patchedast cleanup and refactoring (@lieryan)
 - #905 Ignore `node_modules` directories by default when scanning project files and source folders. (@marcoeangeli)
+- #926, #929 Raise RefactoringError instead of IndexError/ModuleSyntaxError when extracting an empty or whitespace-only region (@aliassar)
 - #933 Add type annotations to project.py (@lieryan)
 - #119, #928 Fix IndexError in rename and find occurrences when a `from` import is the last thing in a module without a trailing newline (@mcepl)
 - #921 Patch the else suite of try statements that also have a finally (@marlon-costa-dc)

rope/refactor/extract.py

@@ -442,6 +442,10 @@ def __call__(self, info):
             self.multi_line_conditions(info)
 
     def base_conditions(self, info):
+        if not info.extracted.strip():
+            raise RefactoringError(
+                "Extracted piece should contain at least one expression or statement."
+            )
         if info.region[1] > info.scope_region[1]:
             raise RefactoringError("Bad region selected for extract method")
 

ropetest/refactor/extracttest.py

@@ -472,6 +472,36 @@ class AClass(object):
         with self.assertRaises(rope.base.exceptions.RefactoringError):
             self.do_extract_method(code, start, end, "new_func")
 
+    def test_extract_method_empty_region(self):
+        code = dedent("""\
+            def a_func(arg):
+                var = arg + 1
+                return var
+        """)
+        start = code.index("arg + 1")
+        with self.assertRaises(rope.base.exceptions.RefactoringError):
+            self.do_extract_method(code, start, start, "new_func")
+
+    def test_extract_method_whitespace_only_region(self):
+        code = dedent("""\
+            def a_func(arg):
+                var = arg + 1
+                return var
+        """)
+        start = code.index("    var")
+        with self.assertRaises(rope.base.exceptions.RefactoringError):
+            self.do_extract_method(code, start, start + 4, "new_func")
+
+    def test_extract_variable_empty_region(self):
+        code = dedent("""\
+            def a_func(arg):
+                var = arg + 1
+                return var
+        """)
+        start = code.index("arg + 1")
+        with self.assertRaises(rope.base.exceptions.RefactoringError):
+            self.do_extract_variable(code, start, start, "new_var")
+
     def test_extract_method_containing_return(self):
         code = dedent("""\
             def a_func(arg):