[Python-checkins] [3.11] GH-94694: Fix column offsets for multi-line method lookups (GH-94721)

[brandtbucher]

https://github.com/python/cpython/commit/e5c8ad3e1518f81f7651d82bbadf5af5e3f402a7
commit: e5c8ad3e1518f81f7651d82bbadf5af5e3f402a7
branch: 3.11
author: Brandt Bucher <brandtbucher at microsoft.com>
committer: brandtbucher <brandtbucher at gmail.com>
date: 2022-07-09T22:12:45-07:00
summary:

[3.11] GH-94694: Fix column offsets for multi-line method lookups (GH-94721)

(cherry picked from commit 264b3ddfd561d97204ffb30be6a7d1fb0555e560)

files:
A Misc/NEWS.d/next/Core and Builtins/2022-07-08-16-44-11.gh-issue-94694.VkL2CM.rst
M Lib/test/test_compile.py
M Lib/test/test_traceback.py
M Python/compile.c

diff --git a/Lib/test/test_compile.py b/Lib/test/test_compile.py
index d113a00088f2c..80b32dee0665f 100644
--- a/Lib/test/test_compile.py
+++ b/Lib/test/test_compile.py
@@ -1145,6 +1145,27 @@ def test_complex_single_line_expression(self):
         self.assertOpcodeSourcePositionIs(compiled_code, 'BINARY_OP',
             line=1, end_line=1, column=0, end_column=27, occurrence=4)
 
+    def test_multiline_assert_rewritten_as_method_call(self):
+        # GH-94694: Don't crash if pytest rewrites a multiline assert as a
+        # method call with the same location information:
+        tree = ast.parse("assert (\n42\n)")
+        old_node = tree.body[0]
+        new_node = ast.Expr(
+            ast.Call(
+                ast.Attribute(
+                    ast.Name("spam", ast.Load()),
+                    "eggs",
+                    ast.Load(),
+                ),
+                [],
+                [],
+            )
+        )
+        ast.copy_location(new_node, old_node)
+        ast.fix_missing_locations(new_node)
+        tree.body[0] = new_node
+        compile(tree, "<test>", "exec")
+
 
 class TestExpressionStackSize(unittest.TestCase):
     # These tests check that the computed stack size for a code object
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index e8ff4b5a28f55..40d5a84f92d99 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -703,6 +703,57 @@ class A: pass
         )
         self.assertEqual(result_lines, expected_error.splitlines())
 
+    def test_multiline_method_call_a(self):
+        def f():
+            (None
+                .method
+            )()
+        actual = self.get_exception(f)
+        expected = [
+            f"Traceback (most recent call last):",
+            f"  File \"{__file__}\", line {self.callable_line}, in get_exception",
+            f"    callable()",
+            f"    ^^^^^^^^^^",
+            f"  File \"{__file__}\", line {f.__code__.co_firstlineno + 2}, in f",
+            f"    .method",
+            f"     ^^^^^^",
+        ]
+        self.assertEqual(actual, expected)
+
+    def test_multiline_method_call_b(self):
+        def f():
+            (None.
+                method
+            )()
+        actual = self.get_exception(f)
+        expected = [
+            f"Traceback (most recent call last):",
+            f"  File \"{__file__}\", line {self.callable_line}, in get_exception",
+            f"    callable()",
+            f"    ^^^^^^^^^^",
+            f"  File \"{__file__}\", line {f.__code__.co_firstlineno + 2}, in f",
+            f"    method",
+            f"    ^^^^^^",
+        ]
+        self.assertEqual(actual, expected)
+
+    def test_multiline_method_call_c(self):
+        def f():
+            (None
+                . method
+            )()
+        actual = self.get_exception(f)
+        expected = [
+            f"Traceback (most recent call last):",
+            f"  File \"{__file__}\", line {self.callable_line}, in get_exception",
+            f"    callable()",
+            f"    ^^^^^^^^^^",
+            f"  File \"{__file__}\", line {f.__code__.co_firstlineno + 2}, in f",
+            f"    . method",
+            f"      ^^^^^^",
+        ]
+        self.assertEqual(actual, expected)
+
 @cpython_only
 @requires_debug_ranges()
 class CPythonTracebackErrorCaretTests(TracebackErrorLocationCaretTests):
diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-07-08-16-44-11.gh-issue-94694.VkL2CM.rst b/Misc/NEWS.d/next/Core and Builtins/2022-07-08-16-44-11.gh-issue-94694.VkL2CM.rst
new file mode 100644
index 0000000000000..6434788140f42
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-07-08-16-44-11.gh-issue-94694.VkL2CM.rst	
@@ -0,0 +1,4 @@
+Fix an issue that could cause code with multi-line method lookups to have
+misleading or incorrect column offset information. In some cases (when
+compiling a hand-built AST) this could have resulted in a hard crash of the
+interpreter.
diff --git a/Python/compile.c b/Python/compile.c
index a71e7d31eecd2..42f3730e220f5 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -4788,8 +4788,15 @@ update_location_to_match_attr(struct compiler *c, expr_ty meth)
 {
     if (meth->lineno != meth->end_lineno) {
         // Make start location match attribute
-        c->u->u_lineno = meth->end_lineno;
-        c->u->u_col_offset = meth->end_col_offset - (int)PyUnicode_GetLength(meth->v.Attribute.attr)-1;
+        c->u->u_lineno = c->u->u_end_lineno = meth->end_lineno;
+        int len = (int)PyUnicode_GET_LENGTH(meth->v.Attribute.attr);
+        if (len <= meth->end_col_offset) {
+            c->u->u_col_offset = meth->end_col_offset - len;
+        }
+        else {
+            // GH-94694: Somebody's compiling weird ASTs. Just drop the columns:
+            c->u->u_col_offset = c->u->u_end_col_offset = -1;
+        }
     }
 }