Avoid index-out-of-bands panic for positional placeholders (#4872)

crates/ruff/resources/test/fixtures/pyflakes/F523.py

@@ -26,6 +26,7 @@
 # With modified indexes
 "{1}{2}".format(1, 2, 3)  # F523, # F524
 "{1}{3}".format(1, 2, 3, 4)  # F523, # F524
+"{1} {8}".format(0, 1)  # F523, # F524
 
 # Not fixable
 (''

crates/ruff/resources/test/fixtures/pyflakes/F524.py

@@ -4,3 +4,4 @@
 "{0} {bar}".format(1)  # F524
 "{0} {bar}".format()  # F524
 "{bar} {0}".format()  # F524
+"{1} {8}".format(0, 1)

crates/ruff/src/rules/pyflakes/fixes.rs

@@ -95,7 +95,7 @@ fn update_field_types(format_string: &FormatString, index_map: &[usize]) -> Stri
                 let new_field_name = FieldName::parse(field_name).unwrap();
                 let mut new_field_name_string = match new_field_name.field_type {
                     FieldType::Auto => String::new(),
-                    FieldType::Index(i) => index_map[i].to_string(),
+                    FieldType::Index(i) => index_map.get(i).unwrap_or(&i).to_string(),
                     FieldType::Keyword(keyword) => keyword,
                 };
                 for field_name_part in &new_field_name.parts {

crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F523_F523.py.snap

@@ -251,6 +251,7 @@ F523.py:27:1: F523 [*] `.format` call has unused arguments at position(s): 0
 28 | "{1}{2}".format(1, 2, 3)  # F523, # F524
    | ^^^^^^^^^^^^^^^^^^^^^^^^ F523
 29 | "{1}{3}".format(1, 2, 3, 4)  # F523, # F524
+30 | "{1} {8}".format(0, 1)  # F523, # F524
    |
    = help: Remove extra positional arguments at position(s): 0
 
@@ -261,8 +262,8 @@ F523.py:27:1: F523 [*] `.format` call has unused arguments at position(s): 0
 27    |-"{1}{2}".format(1, 2, 3)  # F523, # F524
    27 |+"{0}{1}".format(2, 3)  # F523, # F524
 28 28 | "{1}{3}".format(1, 2, 3, 4)  # F523, # F524
-29 29 | 
+29 29 | "{1} {8}".format(0, 1)  # F523, # F524
-30 30 | # Not fixable
+30 30 | 
 
 F523.py:28:1: F523 [*] `.format` call has unused arguments at position(s): 0, 2
    |
@@ -270,8 +271,7 @@ F523.py:28:1: F523 [*] `.format` call has unused arguments at position(s): 0, 2
 29 | "{1}{2}".format(1, 2, 3)  # F523, # F524
 30 | "{1}{3}".format(1, 2, 3, 4)  # F523, # F524
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ F523
-31 | 
+31 | "{1} {8}".format(0, 1)  # F523, # F524
-32 | # Not fixable
    |
    = help: Remove extra positional arguments at position(s): 0, 2
 
@@ -281,16 +281,37 @@ F523.py:28:1: F523 [*] `.format` call has unused arguments at position(s): 0, 2
 27 27 | "{1}{2}".format(1, 2, 3)  # F523, # F524
 28    |-"{1}{3}".format(1, 2, 3, 4)  # F523, # F524
    28 |+"{0}{1}".format(2, 4)  # F523, # F524
-29 29 | 
+29 29 | "{1} {8}".format(0, 1)  # F523, # F524
-30 30 | # Not fixable
+30 30 | 
-31 31 | (''
+31 31 | # Not fixable
 
-F523.py:31:2: F523 `.format` call has unused arguments at position(s): 0
+F523.py:29:1: F523 [*] `.format` call has unused arguments at position(s): 0
    |
-31 |   # Not fixable
+29 | "{1}{2}".format(1, 2, 3)  # F523, # F524
-32 |   (''
+30 | "{1}{3}".format(1, 2, 3, 4)  # F523, # F524
+31 | "{1} {8}".format(0, 1)  # F523, # F524
+   | ^^^^^^^^^^^^^^^^^^^^^^ F523
+32 | 
+33 | # Not fixable
+   |
+   = help: Remove extra positional arguments at position(s): 0
+
+ℹ Suggested fix
+26 26 | # With modified indexes
+27 27 | "{1}{2}".format(1, 2, 3)  # F523, # F524
+28 28 | "{1}{3}".format(1, 2, 3, 4)  # F523, # F524
+29    |-"{1} {8}".format(0, 1)  # F523, # F524
+   29 |+"{0} {8}".format(1)  # F523, # F524
+30 30 | 
+31 31 | # Not fixable
+32 32 | (''
+
+F523.py:32:2: F523 `.format` call has unused arguments at position(s): 0
+   |
+32 |   # Not fixable
+33 |   (''
    |  __^
-33 | | .format(2))
+34 | | .format(2))
    | |__________^ F523
    |
    = help: Remove extra positional arguments at position(s): 0

crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F524_F524.py.snap

@@ -45,6 +45,7 @@ F524.py:5:1: F524 `.format` call is missing argument(s) for placeholder(s): 0, b
 7 | "{0} {bar}".format()  # F524
   | ^^^^^^^^^^^^^^^^^^^^ F524
 8 | "{bar} {0}".format()  # F524
+9 | "{1} {8}".format(0, 1)
   |
 
 F524.py:6:1: F524 `.format` call is missing argument(s) for placeholder(s): 0, bar
@@ -53,6 +54,15 @@ F524.py:6:1: F524 `.format` call is missing argument(s) for placeholder(s): 0, b
 7 | "{0} {bar}".format()  # F524
 8 | "{bar} {0}".format()  # F524
   | ^^^^^^^^^^^^^^^^^^^^ F524
+9 | "{1} {8}".format(0, 1)
+  |
+
+F524.py:7:1: F524 `.format` call is missing argument(s) for placeholder(s): 8
+  |
+7 | "{0} {bar}".format()  # F524
+8 | "{bar} {0}".format()  # F524
+9 | "{1} {8}".format(0, 1)
+  | ^^^^^^^^^^^^^^^^^^^^^^ F524
   |