[PLW1507] Mark fix unsafe (#16343)

crates/ruff_linter/resources/test/fixtures/pylint/shallow_copy_environ.py

@@ -2,3 +2,11 @@ import copy
 import os
 
 copied_env = copy.copy(os.environ)  # [shallow-copy-environ]
+
+
+# Test case where the proposed fix is wrong, i.e., unsafe fix
+# Ref: https://github.com/astral-sh/ruff/issues/16274#event-16423475135
+
+os.environ["X"] = "0"
+env = copy.copy(os.environ)
+os.environ["X"] = "1"

crates/ruff_linter/src/rules/pylint/rules/shallow_copy_environ.rs

@@ -30,6 +30,13 @@ use crate::checkers::ast::Checker;
 /// env = os.environ.copy()
 /// ```
 ///
+/// ## Fix safety
+///
+/// This rule's fix is marked as unsafe because replacing a shallow copy with a deep copy can lead
+/// to unintended side effects. If the program modifies the shallow copy at some point, changing it
+/// to a deep copy may prevent those modifications from affecting the original data, potentially
+/// altering the program's behavior.
+///
 /// ## References
 /// - [Python documentation: `copy` — Shallow and deep copy operations](https://docs.python.org/3/library/copy.html)
 /// - [Python documentation: `os.environ`](https://docs.python.org/3/library/os.html#os.environ)
@@ -82,7 +89,7 @@ pub(crate) fn shallow_copy_environ(checker: &Checker, call: &ast::ExprCall) {
     }
 
     let mut diagnostic = Diagnostic::new(ShallowCopyEnviron, call.range());
-    diagnostic.set_fix(Fix::safe_edit(Edit::range_replacement(
+    diagnostic.set_fix(Fix::unsafe_edit(Edit::range_replacement(
         format!("{}.copy()", checker.locator().slice(arg)),
         call.range(),
     )));

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLW1507_shallow_copy_environ.py.snap

@@ -10,9 +10,29 @@ shallow_copy_environ.py:4:14: PLW1507 [*] Shallow copy of `os.environ` via `copy
   |
   = help: Replace with `os.environ.copy()`
 
-ℹ Safe fix
+ℹ Unsafe fix
 1 1 | import copy
 2 2 | import os
 3 3 | 
 4   |-copied_env = copy.copy(os.environ)  # [shallow-copy-environ]
   4 |+copied_env = os.environ.copy()  # [shallow-copy-environ]
+5 5 | 
+6 6 | 
+7 7 | # Test case where the proposed fix is wrong, i.e., unsafe fix
+
+shallow_copy_environ.py:11:7: PLW1507 [*] Shallow copy of `os.environ` via `copy.copy(os.environ)`
+   |
+10 | os.environ["X"] = "0"
+11 | env = copy.copy(os.environ)
+   |       ^^^^^^^^^^^^^^^^^^^^^ PLW1507
+12 | os.environ["X"] = "1"
+   |
+   = help: Replace with `os.environ.copy()`
+
+ℹ Unsafe fix
+8  8  | # Ref: https://github.com/astral-sh/ruff/issues/16274#event-16423475135
+9  9  | 
+10 10 | os.environ["X"] = "0"
+11    |-env = copy.copy(os.environ)
+   11 |+env = os.environ.copy()
+12 12 | os.environ["X"] = "1"