Ensure N811 flags single-character constants imported as lowercase

crates/ruff_linter/resources/test/fixtures/pep8_naming/N811.py

@@ -2,6 +2,8 @@
 from mod import CONSTANT as constant
 from mod import ANOTHER_CONSTANT as another_constant
 import mod.CON as c
+from mod import C as c
 
+# These are all OK:
 import django.db.models.Q as Query1
 from django.db.models import Q as Query2

crates/ruff_linter/resources/test/fixtures/pep8_naming/N814.py

@@ -2,5 +2,6 @@
 from mod import CamelCase as CAMELCASE
 from mod import AnotherCamelCase as ANOTHER_CAMELCASE
 
+# These are all OK:
 import mod.AppleFruit as A
 from mod import BananaFruit as B

crates/ruff_linter/src/rules/pep8_naming/rules/constant_imported_as_non_constant.rs

@@ -4,7 +4,7 @@ use ruff_python_ast::{Alias, Stmt};
 use ruff_python_stdlib::str;
 use ruff_text_size::Ranged;
 
-use crate::rules::pep8_naming::settings::IgnoreNames;
+use crate::rules::pep8_naming::{helpers, settings::IgnoreNames};
 
 /// ## What it does
 /// Checks for constant imports that are aliased to non-constant-style
@@ -65,10 +65,13 @@ pub(crate) fn constant_imported_as_non_constant(
     stmt: &Stmt,
     ignore_names: &IgnoreNames,
 ) -> Option<Diagnostic> {
-    // Single-character names are ambiguous. It could be a class or a constant.
-    name.chars().nth(1)?;
-
-    if str::is_cased_uppercase(name) && !str::is_cased_uppercase(asname) {
+    if str::is_cased_uppercase(name)
+        && !(str::is_cased_uppercase(asname)
+            // Single-character names are ambiguous.
+            // It could be a class or a constant, so allow it to be imported
+            // as `SCREAMING_SNAKE_CASE` *or* `CamelCase`.
+            || (name.chars().nth(1).is_none()) && helpers::is_camelcase(asname))
+    {
         // Ignore any explicitly-allowed names.
         if ignore_names.matches(name) || ignore_names.matches(asname) {
             return None;

crates/ruff_linter/src/rules/pep8_naming/snapshots/ruff_linter__rules__pep8_naming__tests__N811_N811.py.snap

@@ -1,6 +1,5 @@
 ---
 source: crates/ruff_linter/src/rules/pep8_naming/mod.rs
-snapshot_kind: text
 ---
 N811.py:1:8: N811 Constant `CONST` imported as non-constant `const`
   |
@@ -26,6 +25,7 @@ N811.py:3:17: N811 Constant `ANOTHER_CONSTANT` imported as non-constant `another
 3 | from mod import ANOTHER_CONSTANT as another_constant
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ N811
 4 | import mod.CON as c
+5 | from mod import C as c
   |
 
 N811.py:4:8: N811 Constant `CON` imported as non-constant `c`
@@ -34,6 +34,15 @@ N811.py:4:8: N811 Constant `CON` imported as non-constant `c`
 3 | from mod import ANOTHER_CONSTANT as another_constant
 4 | import mod.CON as c
   |        ^^^^^^^^^^^^ N811
-5 | 
-6 | import django.db.models.Q as Query1
+5 | from mod import C as c
+  |
+
+N811.py:5:17: N811 Constant `C` imported as non-constant `c`
+  |
+3 | from mod import ANOTHER_CONSTANT as another_constant
+4 | import mod.CON as c
+5 | from mod import C as c
+  |                 ^^^^^^ N811
+6 | 
+7 | # These are all OK:
   |

crates/ruff_linter/src/rules/pep8_naming/snapshots/ruff_linter__rules__pep8_naming__tests__N814_N814.py.snap

@@ -1,6 +1,5 @@
 ---
 source: crates/ruff_linter/src/rules/pep8_naming/mod.rs
-snapshot_kind: text
 ---
 N814.py:1:8: N814 Camelcase `Camel` imported as constant `CAMEL`
   |
@@ -25,5 +24,5 @@ N814.py:3:17: N814 Camelcase `AnotherCamelCase` imported as constant `ANOTHER_CA
 3 | from mod import AnotherCamelCase as ANOTHER_CAMELCASE
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ N814
 4 | 
-5 | import mod.AppleFruit as A
+5 | # These are all OK:
   |