Add error handling for extract of incomplete block

CHANGELOG.md

@@ -12,6 +12,7 @@
 - #719 Allows the in-memory db to be shared across threads (@tkrabel)
 - #720 create one sqlite3.Connection per thread using a thread local (@tkrabel)
 - #715 change AutoImport's `get_modules` to be case sensitive (@bagel897)
+- #734 raise exception when extracting the start of a block without the end
 
 # Release 1.10.0
 

rope/refactor/extract.py

@@ -444,8 +444,10 @@ def __call__(self, info):
     def base_conditions(self, info):
         if info.region[1] > info.scope_region[1]:
             raise RefactoringError("Bad region selected for extract method")
+
         end_line = info.region_lines[1]
         end_scope = info.global_scope.get_inner_scope_for_line(end_line)
+
         if end_scope != info.scope and end_scope.get_end() != end_line:
             raise RefactoringError("Bad region selected for extract method")
         try:
@@ -497,6 +499,14 @@ def multi_line_conditions(self, info):
             raise RefactoringError(
                 "Extracted piece should contain complete statements."
             )
+        unbalanced_region_finder = _UnbalancedRegionFinder(
+            info.region_lines[0], info.region_lines[1]
+        )
+        unbalanced_region_finder.visit(info.pymodule.ast_node)
+        if unbalanced_region_finder.error:
+            raise RefactoringError(
+                "Extracted piece cannot contain the start of a block without the end."
+            )
 
     def _is_region_on_a_word(self, info):
         if (
@@ -1093,6 +1103,34 @@ def _ClassDef(self, node):
         pass
 
 
+class _UnbalancedRegionFinder(_BaseErrorFinder):
+    """
+    Flag an error if we are including the start of a block without the end.
+    We detect this by ensuring there is no AST node that starts inside the
+    selected range but ends outside of it.
+    """
+
+    def __init__(self, line_start: int, line_end: int):
+        self.error = False
+        self.line_start = line_start
+        self.line_end = line_end
+
+    def generic_visit(self, node: ast.AST):
+        if not hasattr(node, "end_lineno"):
+            super().generic_visit(node)  # Visit children
+            return
+        ends_before_range_starts = node.end_lineno < self.line_start
+        starts_after_range_ends = node.lineno > self.line_end
+        if ends_before_range_starts or starts_after_range_ends:
+            return  # Don't visit children
+        starts_on_or_after_range_start = node.lineno >= self.line_start
+        ends_after_range_ends = node.end_lineno > self.line_end
+        if starts_on_or_after_range_start and ends_after_range_ends:
+            self.error = True
+            return  # Don't visit children
+        super().generic_visit(node)  # Visit children
+
+
 class _GlobalFinder(ast.RopeNodeVisitor):
     def __init__(self):
         self.globals_ = OrderedSet()

ropetest/refactor/extracttest.py

@@ -1149,6 +1149,64 @@ def xxx_test_raising_exception_on_function_parens(self):
         end = code.rindex(")") + 1
         with self.assertRaises(rope.base.exceptions.RefactoringError):
             self.do_extract_method(code, start, end, "new_func")
+
+    def test_raising_exception_on_incomplete_block(self):
+        code = dedent("""\
+            if True:
+                a = 1
+                b = 2
+        """)
+        start = code.index("if")
+        end = code.index("1") + 1
+        with self.assertRaises(rope.base.exceptions.RefactoringError):
+            self.do_extract_method(code, start, end, "new_func")
+
+    def test_raising_exception_on_incomplete_block_2(self):
+        code = dedent("""\
+            if True:
+                a = 1
+            #
+                b = 2
+        """)
+        start = code.index("if")
+        end = code.index("1") + 1
+        with self.assertRaises(rope.base.exceptions.RefactoringError):
+            self.do_extract_method(code, start, end, "new_func")
+
+    def test_raising_exception_on_incomplete_block_3(self):
+        code = dedent("""\
+            if True:
+                a = 1
+
+                b = 2
+        """)
+        start = code.index("if")
+        end = code.index("1") + 1
+        with self.assertRaises(rope.base.exceptions.RefactoringError):
+            self.do_extract_method(code, start, end, "new_func")
+
+    def test_raising_exception_on_incomplete_block_4(self):
+        code = dedent("""\
+                #
+            if True:
+                a = 1
+                b = 2
+        """)
+        start = code.index("#")
+        end = code.index("1") + 1
+        with self.assertRaises(rope.base.exceptions.RefactoringError):
+            self.do_extract_method(code, start, end, "new_func")
+
+    def test_raising_exception_on_incomplete_block_5(self):
+        code = dedent("""\
+            if True:
+                if 0:
+                    a = 1
+        """)
+        start = code.index("if")
+        end = code.index("0:") + 2
+        with self.assertRaises(rope.base.exceptions.RefactoringError):
+            self.do_extract_method(code, start, end, "new_func")
 
     def test_extract_method_and_extra_blank_lines(self):
         code = dedent("""\