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Fix syntax error false positive on alternative `match` patterns (#21362) 

Summary
--

Fixes #21360 by using the union of names instead of overwriting them, as
Micha suggested originally on #21104.

This avoids overwriting the `n` name in the `Subscript` by the empty set
of names visited in the nested OR pattern before visiting the other arm
of the outer OR pattern.

Test Plan
--

A new inline test case taken from the issue
This commit is contained in:
Brent Westbrook 2025-11-10 10:51:51 -05:00 committed by GitHub
parent 8d1efe964a
commit 835e31b3ff
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GPG Key ID: B5690EEEBB952194
3 changed files with 216 additions and 2 deletions
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2
crates/ruff_python_parser/resources/inline/ok/nested_alternative_patterns.py
View File

@ -5,3 +5,5 @@ match 42:
case [[x] | [x]] | x: ...
match 42:
case [[x | x] | [x]] | x: ...
match 42:
case ast.Subscript(n, ast.Constant() | ast.Slice()) | ast.Attribute(n): ...

4
crates/ruff_python_parser/src/semantic_errors.rs
View File

@ -1868,6 +1868,8 @@ impl<'a, Ctx: SemanticSyntaxContext> MatchPatternVisitor<'a, Ctx> {
// case [[x] | [x]] | x: ...
// match 42:
// case [[x | x] | [x]] | x: ...
// match 42:
// case ast.Subscript(n, ast.Constant() | ast.Slice()) | ast.Attribute(n): ...
SemanticSyntaxChecker::add_error(
self.ctx,
SemanticSyntaxErrorKind::DifferentMatchPatternBindings,
@ -1875,7 +1877,7 @@ impl<'a, Ctx: SemanticSyntaxContext> MatchPatternVisitor<'a, Ctx> {
);
break;
}
self.names = visitor.names;
self.names.extend(visitor.names);
}
}
}

212
crates/ruff_python_parser/tests/snapshots/valid_syntax@nested_alternative_patterns.py.snap
View File

@ -8,7 +8,7 @@ input_file: crates/ruff_python_parser/resources/inline/ok/nested_alternative_pat
Module(
ModModule {
node_index: NodeIndex(None),
range: 0..181,
range: 0..271,
body: [
Match(
StmtMatch {
@ -489,6 +489,216 @@ Module(
],
},
),
Match(
StmtMatch {
node_index: NodeIndex(None),
range: 181..270,
subject: NumberLiteral(
ExprNumberLiteral {
node_index: NodeIndex(None),
range: 187..189,
value: Int(
42,
),
},
),
cases: [
MatchCase {
range: 195..270,
node_index: NodeIndex(None),
pattern: MatchOr(
PatternMatchOr {
node_index: NodeIndex(None),
range: 200..265,
patterns: [
MatchClass(
PatternMatchClass {
node_index: NodeIndex(None),
range: 200..246,
cls: Attribute(
ExprAttribute {
node_index: NodeIndex(None),
range: 200..213,
value: Name(
ExprName {
node_index: NodeIndex(None),
range: 200..203,
id: Name("ast"),
ctx: Load,
},
),
attr: Identifier {
id: Name("Subscript"),
range: 204..213,
node_index: NodeIndex(None),
},
ctx: Load,
},
),
arguments: PatternArguments {
range: 213..246,
node_index: NodeIndex(None),
patterns: [
MatchAs(
PatternMatchAs {
node_index: NodeIndex(None),
range: 214..215,
pattern: None,
name: Some(
Identifier {
id: Name("n"),
range: 214..215,
node_index: NodeIndex(None),
},
),
},
),
MatchOr(
PatternMatchOr {
node_index: NodeIndex(None),
range: 217..245,
patterns: [
MatchClass(
PatternMatchClass {
node_index: NodeIndex(None),
range: 217..231,
cls: Attribute(
ExprAttribute {
node_index: NodeIndex(None),
range: 217..229,
value: Name(
ExprName {
node_index: NodeIndex(None),
range: 217..220,
id: Name("ast"),
ctx: Load,
},
),
attr: Identifier {
id: Name("Constant"),
range: 221..229,
node_index: NodeIndex(None),
},
ctx: Load,
},
),
arguments: PatternArguments {
range: 229..231,
node_index: NodeIndex(None),
patterns: [],
keywords: [],
},
},
),
MatchClass(
PatternMatchClass {
node_index: NodeIndex(None),
range: 234..245,
cls: Attribute(
ExprAttribute {
node_index: NodeIndex(None),
range: 234..243,
value: Name(
ExprName {
node_index: NodeIndex(None),
range: 234..237,
id: Name("ast"),
ctx: Load,
},
),
attr: Identifier {
id: Name("Slice"),
range: 238..243,
node_index: NodeIndex(None),
},
ctx: Load,
},
),
arguments: PatternArguments {
range: 243..245,
node_index: NodeIndex(None),
patterns: [],
keywords: [],
},
},
),
],
},
),
],
keywords: [],
},
},
),
MatchClass(
PatternMatchClass {
node_index: NodeIndex(None),
range: 249..265,
cls: Attribute(
ExprAttribute {
node_index: NodeIndex(None),
range: 249..262,
value: Name(
ExprName {
node_index: NodeIndex(None),
range: 249..252,
id: Name("ast"),
ctx: Load,
},
),
attr: Identifier {
id: Name("Attribute"),
range: 253..262,
node_index: NodeIndex(None),
},
ctx: Load,
},
),
arguments: PatternArguments {
range: 262..265,
node_index: NodeIndex(None),
patterns: [
MatchAs(
PatternMatchAs {
node_index: NodeIndex(None),
range: 263..264,
pattern: None,
name: Some(
Identifier {
id: Name("n"),
range: 263..264,
node_index: NodeIndex(None),
},
),
},
),
],
keywords: [],
},
},
),
],
},
),
guard: None,
body: [
Expr(
StmtExpr {
node_index: NodeIndex(None),
range: 267..270,
value: EllipsisLiteral(
ExprEllipsisLiteral {
node_index: NodeIndex(None),
range: 267..270,
},
),
},
),
],
},
],
},
),
],
},
)