RUF064: offer a safe fix for multi-digit zeros (#19847)

Fixes #19010

## Summary

See #19010. `0` was not considered a violation, but `000` was. The
latter will now be fixed to `0o000`.

crates/ruff_linter/resources/test/fixtures/ruff/RUF064.py

@@ -51,3 +51,11 @@ dbm.ndbm.open("db", "r", 0o600)  # OK
 
 os.fchmod(0, 256)  # 0o400
 os.fchmod(0, 493)  # 0o755
+
+# https://github.com/astral-sh/ruff/issues/19010
+os.chmod("foo", 000)  # Error
+os.chmod("foo", 0000)  # Error
+
+os.chmod("foo", 0b0)  # Error
+os.chmod("foo", 0x0)  # Error
+os.chmod("foo", 0)  # Ok

crates/ruff_linter/src/rules/ruff/rules/non_octal_permissions.rs

@@ -57,6 +57,17 @@ use crate::{FixAvailability, Violation};
 /// original code really intended to use `0o256` (`u=w,g=rx,o=rw`) instead of
 /// `256`, this fix should not be accepted.
 ///
+/// As a special case, zero is allowed to omit the `0o` prefix unless it has
+/// multiple digits:
+///
+/// ```python
+/// os.chmod("foo", 0)  # Ok
+/// os.chmod("foo", 0o000)  # Ok
+/// os.chmod("foo", 000)  # Lint emitted and fix suggested
+/// ```
+///
+/// Ruff will suggest a safe fix for multi-digit zeros to add the `0o` prefix.
+///
 /// ## Fix availability
 ///
 /// A fix is only available if the integer literal matches a set of common modes.
@@ -102,7 +113,14 @@ pub(crate) fn non_octal_permissions(checker: &Checker, call: &ExprCall) {
     let mut diagnostic = checker.report_diagnostic(NonOctalPermissions, mode_arg.range());
 
     // Don't suggest a fix for 0x or 0b literals.
-    if mode_literal.starts_with('0') {
+    if mode_literal.starts_with("0x") || mode_literal.starts_with("0b") {
+        return;
+    }
+
+    if mode_literal.chars().all(|c| c == '0') {
+        // Fix e.g. 000 as 0o000
+        let edit = Edit::range_replacement(format!("0o{mode_literal}"), mode_arg.range());
+        diagnostic.set_fix(Fix::safe_edit(edit));
         return;
     }
 

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__RUF064_RUF064.py.snap

@@ -348,6 +348,8 @@ help: Replace with octal literal
 52    |-os.fchmod(0, 256)  # 0o400
    52 |+os.fchmod(0, 0o400)  # 0o400
 53 53 | os.fchmod(0, 493)  # 0o755
+54 54 | 
+55 55 | # https://github.com/astral-sh/ruff/issues/19010
 
 RUF064 [*] Non-octal mode
   --> RUF064.py:53:14
@@ -355,6 +357,8 @@ RUF064 [*] Non-octal mode
 52 | os.fchmod(0, 256)  # 0o400
 53 | os.fchmod(0, 493)  # 0o755
    |              ^^^
+54 |
+55 | # https://github.com/astral-sh/ruff/issues/19010
    |
 help: Replace with octal literal
 
@@ -364,3 +368,70 @@ help: Replace with octal literal
 52 52 | os.fchmod(0, 256)  # 0o400
 53    |-os.fchmod(0, 493)  # 0o755
    53 |+os.fchmod(0, 0o755)  # 0o755
+54 54 | 
+55 55 | # https://github.com/astral-sh/ruff/issues/19010
+56 56 | os.chmod("foo", 000)  # Error
+
+RUF064 [*] Non-octal mode
+  --> RUF064.py:56:17
+   |
+55 | # https://github.com/astral-sh/ruff/issues/19010
+56 | os.chmod("foo", 000)  # Error
+   |                 ^^^
+57 | os.chmod("foo", 0000)  # Error
+   |
+help: Replace with octal literal
+
+ℹ Safe fix
+53 53 | os.fchmod(0, 493)  # 0o755
+54 54 | 
+55 55 | # https://github.com/astral-sh/ruff/issues/19010
+56    |-os.chmod("foo", 000)  # Error
+   56 |+os.chmod("foo", 0o000)  # Error
+57 57 | os.chmod("foo", 0000)  # Error
+58 58 | 
+59 59 | os.chmod("foo", 0b0)  # Error
+
+RUF064 [*] Non-octal mode
+  --> RUF064.py:57:17
+   |
+55 | # https://github.com/astral-sh/ruff/issues/19010
+56 | os.chmod("foo", 000)  # Error
+57 | os.chmod("foo", 0000)  # Error
+   |                 ^^^^
+58 |
+59 | os.chmod("foo", 0b0)  # Error
+   |
+help: Replace with octal literal
+
+ℹ Safe fix
+54 54 | 
+55 55 | # https://github.com/astral-sh/ruff/issues/19010
+56 56 | os.chmod("foo", 000)  # Error
+57    |-os.chmod("foo", 0000)  # Error
+   57 |+os.chmod("foo", 0o0000)  # Error
+58 58 | 
+59 59 | os.chmod("foo", 0b0)  # Error
+60 60 | os.chmod("foo", 0x0)  # Error
+
+RUF064 Non-octal mode
+  --> RUF064.py:59:17
+   |
+57 | os.chmod("foo", 0000)  # Error
+58 |
+59 | os.chmod("foo", 0b0)  # Error
+   |                 ^^^
+60 | os.chmod("foo", 0x0)  # Error
+61 | os.chmod("foo", 0)  # Ok
+   |
+help: Replace with octal literal
+
+RUF064 Non-octal mode
+  --> RUF064.py:60:17
+   |
+59 | os.chmod("foo", 0b0)  # Error
+60 | os.chmod("foo", 0x0)  # Error
+   |                 ^^^
+61 | os.chmod("foo", 0)  # Ok
+   |
+help: Replace with octal literal