Fix arithmetic stability issue (#2817)

It turns out "simple_stmt" isn't that simple: it can contain multiple
statements separated by semicolons. Invisible parenthesis logic for
arithmetic expressions only looked at the first child of simple_stmt.
This causes instability in the presence of semicolons, since the next
run through the statement following the semicolon will be the first
child of another simple_stmt.

I believe this along with #2572 fix the known stability issues.

diff --git a/CHANGES.md b/CHANGES.md
index 274c5640ec018adb937502cea2e184dd38337f1d..b57a360f1bce3e6cc4263b35868b6f29f0c453d9 100644 (file)
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -24,6 +24,7 @@ and the first release covered by our new stability policy.
 - Don't add whitespace for attribute access on hexadecimal, binary, octal, and complex
   literals (#2799)
 - Treat blank lines in stubs the same inside top-level `if` statements (#2820)
+- Fix unstable formatting with semicolons and arithmetic expressions (#2817)
 
 ### Parser
 

diff --git a/src/black/linegen.py b/src/black/linegen.py
index b572ed0b52fdbe6d546365ffbce2876466b568d0..495d3230f8fed640f421185fc962ec0714520e4d 100644 (file)
--- a/src/black/linegen.py
+++ b/src/black/linegen.py
@@ -7,7 +7,7 @@ from typing import Collection, Iterator, List, Optional, Set, Union
 
 from black.nodes import WHITESPACE, RARROW, STATEMENT, STANDALONE_COMMENT
 from black.nodes import ASSIGNMENTS, OPENING_BRACKETS, CLOSING_BRACKETS
-from black.nodes import Visitor, syms, first_child_is_arith, ensure_visible
+from black.nodes import Visitor, syms, is_arith_like, ensure_visible
 from black.nodes import is_docstring, is_empty_tuple, is_one_tuple, is_one_tuple_between
 from black.nodes import is_name_token, is_lpar_token, is_rpar_token
 from black.nodes import is_walrus_assignment, is_yield, is_vararg, is_multiline_string
@@ -156,8 +156,12 @@ class LineGenerator(Visitor[Line]):
 
     def visit_simple_stmt(self, node: Node) -> Iterator[Line]:
         """Visit a statement without nested statements."""
-        if first_child_is_arith(node):
-            wrap_in_parentheses(node, node.children[0], visible=False)
+        prev_type: Optional[int] = None
+        for child in node.children:
+            if (prev_type is None or prev_type == token.SEMI) and is_arith_like(child):
+                wrap_in_parentheses(node, child, visible=False)
+            prev_type = child.type
+
         is_suite_like = node.parent and node.parent.type in STATEMENT
         if is_suite_like:
             if self.mode.is_pyi and is_stub_body(node):

diff --git a/src/black/nodes.py b/src/black/nodes.py
index 51d4cb8618d0a6a2c1f8ac1d55318ed2579fb5d9..7466670be5a9864669790b0bd6948217441c435b 100644 (file)
--- a/src/black/nodes.py
+++ b/src/black/nodes.py
@@ -531,15 +531,14 @@ def first_leaf_column(node: Node) -> Optional[int]:
     return None
 
 
-def first_child_is_arith(node: Node) -> bool:
-    """Whether first child is an arithmetic or a binary arithmetic expression"""
-    expr_types = {
+def is_arith_like(node: LN) -> bool:
+    """Whether node is an arithmetic or a binary arithmetic expression"""
+    return node.type in {
         syms.arith_expr,
         syms.shift_expr,
         syms.xor_expr,
         syms.and_expr,
     }
-    return bool(node.children and node.children[0].type in expr_types)
 
 
 def is_docstring(leaf: Leaf) -> bool: