Avoid attempting infinite open fix with re-bound builtin (#3650)

crates/ruff/resources/test/fixtures/pyupgrade/UP020.py

@@ -1,9 +1,9 @@
-from io import open
+import io
 
-with open("f.txt") as f:
+with io.open("f.txt", mode="r", buffering=-1, **kwargs) as f:
     print(f.read())
 
-import io
+from io import open
 
-with io.open("f.txt", mode="r", buffering=-1, **kwargs) as f:
+with open("f.txt") as f:
     print(f.read())

crates/ruff/src/rules/pyupgrade/mod.rs

@@ -38,6 +38,7 @@ mod tests {
     #[test_case(Rule::RedundantOpenModes, Path::new("UP015.py"); "UP015")]
     #[test_case(Rule::NativeLiterals, Path::new("UP018.py"); "UP018")]
     #[test_case(Rule::TypingTextStrAlias, Path::new("UP019.py"); "UP019")]
+    #[test_case(Rule::OpenAlias, Path::new("UP020.py"); "UP020")]
     #[test_case(Rule::ReplaceUniversalNewlines, Path::new("UP021.py"); "UP021")]
     #[test_case(Rule::ReplaceStdoutStderr, Path::new("UP022.py"); "UP022")]
     #[test_case(Rule::DeprecatedCElementTree, Path::new("UP023.py"); "UP023")]

crates/ruff/src/rules/pyupgrade/rules/open_alias.rs

@@ -1,23 +1,28 @@
 use rustpython_parser::ast::Expr;
 
-use ruff_diagnostics::{AlwaysAutofixableViolation, Diagnostic, Fix};
+use ruff_diagnostics::{AutofixKind, Diagnostic, Fix, Violation};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::types::Range;
 
 use crate::checkers::ast::Checker;
 use crate::registry::AsRule;
 
 #[violation]
-pub struct OpenAlias;
+pub struct OpenAlias {
+    pub fixable: bool,
+}
+
+impl Violation for OpenAlias {
+    const AUTOFIX: AutofixKind = AutofixKind::Sometimes;
 
-impl AlwaysAutofixableViolation for OpenAlias {
     #[derive_message_formats]
     fn message(&self) -> String {
         format!("Use builtin `open`")
     }
 
-    fn autofix_title(&self) -> String {
-        "Replace with builtin `open`".to_string()
+    fn autofix_title_formatter(&self) -> Option<fn(&Self) -> String> {
+        self.fixable
+            .then_some(|_| format!("Replace with builtin `open`"))
     }
 }
 
@@ -28,8 +33,12 @@ pub fn open_alias(checker: &mut Checker, expr: &Expr, func: &Expr) {
         .resolve_call_path(func)
         .map_or(false, |call_path| call_path.as_slice() == ["io", "open"])
     {
-        let mut diagnostic = Diagnostic::new(OpenAlias, Range::from(expr));
-        if checker.patch(diagnostic.kind.rule()) {
+        let fixable = checker
+            .ctx
+            .find_binding("open")
+            .map_or(true, |binding| binding.kind.is_builtin());
+        let mut diagnostic = Diagnostic::new(OpenAlias { fixable }, Range::from(expr));
+        if fixable && checker.patch(diagnostic.kind.rule()) {
             diagnostic.amend(Fix::replacement(
                 "open".to_string(),
                 func.location,

crates/ruff/src/rules/pyupgrade/snapshots/ruff__rules__pyupgrade__tests__UP020.py.snap

@@ -0,0 +1,38 @@
+---
+source: crates/ruff/src/rules/pyupgrade/mod.rs
+expression: diagnostics
+---
+- kind:
+    name: OpenAlias
+    body: "Use builtin `open`"
+    suggestion: "Replace with builtin `open`"
+    fixable: true
+  location:
+    row: 3
+    column: 5
+  end_location:
+    row: 3
+    column: 55
+  fix:
+    content: open
+    location:
+      row: 3
+      column: 5
+    end_location:
+      row: 3
+      column: 12
+  parent: ~
+- kind:
+    name: OpenAlias
+    body: "Use builtin `open`"
+    suggestion: ~
+    fixable: false
+  location:
+    row: 8
+    column: 5
+  end_location:
+    row: 8
+    column: 18
+  fix: ~
+  parent: ~
+