Avoid incorrect tuple transformation in single-element case (C409)

crates/ruff_linter/resources/test/fixtures/flake8_comprehensions/C409.py

@@ -16,3 +16,11 @@
 tuple([  # comment
     1, 2
 ])
+
+tuple((
+    1,
+))
+
+t6 = tuple([1])
+t7 = tuple((1,))
+t8 = tuple([1,])

crates/ruff_linter/src/rules/flake8_comprehensions/rules/unnecessary_literal_within_tuple_call.rs

@@ -1,7 +1,8 @@
 use ruff_diagnostics::{AlwaysFixableViolation, Diagnostic, Edit, Fix};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::{self as ast, Expr};
-use ruff_text_size::{Ranged, TextSize};
+use ruff_python_trivia::{SimpleTokenKind, SimpleTokenizer};
+use ruff_text_size::{Ranged, TextRange, TextSize};
 
 use crate::checkers::ast::Checker;
 
@@ -71,9 +72,12 @@ pub(crate) fn unnecessary_literal_within_tuple_call(checker: &mut Checker, call:
     if !call.arguments.keywords.is_empty() {
         return;
     }
-    let Some(argument) =
-        helpers::first_argument_with_matching_function("tuple", &call.func, &call.arguments.args)
-    else {
+    let Some(argument) = helpers::exactly_one_argument_with_matching_function(
+        "tuple",
+        &call.func,
+        &call.arguments.args,
+        &call.arguments.keywords,
+    ) else {
         return;
     };
     if !checker.semantic().is_builtin("tuple") {
@@ -92,23 +96,41 @@ pub(crate) fn unnecessary_literal_within_tuple_call(checker: &mut Checker, call:
         call.range(),
     );
 
-    // Convert `tuple([1, 2])` to `tuple(1, 2)`
+    // Convert `tuple([1, 2])` to `(1, 2)`
     diagnostic.set_fix({
-        // Replace from the start of the call to the start of the inner list or tuple with `(`.
-        let call_start = Edit::replacement(
-            "(".to_string(),
+        let elts = match argument {
+            Expr::List(ast::ExprList { elts, .. }) => elts.as_slice(),
+            Expr::Tuple(ast::ExprTuple { elts, .. }) => elts.as_slice(),
+            _ => return,
+        };
+
+        let needs_trailing_comma = if let [item] = elts {
+            SimpleTokenizer::new(
+                checker.locator().contents(),
+                TextRange::new(item.end(), call.end()),
+            )
+            .all(|token| token.kind != SimpleTokenKind::Comma)
+        } else {
+            false
+        };
+
+        // Replace `[` with `(`.
+        let elt_start = Edit::replacement(
+            "(".into(),
             call.start(),
             argument.start() + TextSize::from(1),
         );
-
-        // Replace from the end of the inner list or tuple to the end of the call with `)`.
-        let call_end = Edit::replacement(
-            ")".to_string(),
+        // Replace `]` with `)` or `,)`.
+        let elt_end = Edit::replacement(
+            if needs_trailing_comma {
+                ",)".into()
+            } else {
+                ")".into()
+            },
             argument.end() - TextSize::from(1),
             call.end(),
         );
-
-        Fix::unsafe_edits(call_start, [call_end])
+        Fix::unsafe_edits(elt_start, [elt_end])
     });
 
     checker.diagnostics.push(diagnostic);

crates/ruff_linter/src/rules/flake8_comprehensions/snapshots/ruff_linter__rules__flake8_comprehensions__tests__C409_C409.py.snap

@@ -143,6 +143,8 @@ C409.py:16:1: C409 [*] Unnecessary `list` literal passed to `tuple()` (rewrite a
 17 | |     1, 2
 18 | | ])
    | |__^ C409
+19 |   
+20 |   tuple((
    |
    = help: Rewrite as a `tuple` literal
 
@@ -155,5 +157,85 @@ C409.py:16:1: C409 [*] Unnecessary `list` literal passed to `tuple()` (rewrite a
 17 17 |     1, 2
 18    |-])
    18 |+)
+19 19 | 
+20 20 | tuple((
+21 21 |     1,
 
+C409.py:20:1: C409 [*] Unnecessary `tuple` literal passed to `tuple()` (remove the outer call to `tuple()`)
+   |
+18 |   ])
+19 |   
+20 | / tuple((
+21 | |     1,
+22 | | ))
+   | |__^ C409
+23 |   
+24 |   t6 = tuple([1])
+   |
+   = help: Remove outer `tuple` call
+
+ℹ Unsafe fix
+17 17 |     1, 2
+18 18 | ])
+19 19 | 
+20    |-tuple((
+   20 |+(
+21 21 |     1,
+22    |-))
+   22 |+)
+23 23 | 
+24 24 | t6 = tuple([1])
+25 25 | t7 = tuple((1,))
+
+C409.py:24:6: C409 [*] Unnecessary `list` literal passed to `tuple()` (rewrite as a `tuple` literal)
+   |
+22 | ))
+23 | 
+24 | t6 = tuple([1])
+   |      ^^^^^^^^^^ C409
+25 | t7 = tuple((1,))
+26 | t8 = tuple([1,])
+   |
+   = help: Rewrite as a `tuple` literal
+
+ℹ Unsafe fix
+21 21 |     1,
+22 22 | ))
+23 23 | 
+24    |-t6 = tuple([1])
+   24 |+t6 = (1,)
+25 25 | t7 = tuple((1,))
+26 26 | t8 = tuple([1,])
+
+C409.py:25:6: C409 [*] Unnecessary `tuple` literal passed to `tuple()` (remove the outer call to `tuple()`)
+   |
+24 | t6 = tuple([1])
+25 | t7 = tuple((1,))
+   |      ^^^^^^^^^^^ C409
+26 | t8 = tuple([1,])
+   |
+   = help: Remove outer `tuple` call
+
+ℹ Unsafe fix
+22 22 | ))
+23 23 | 
+24 24 | t6 = tuple([1])
+25    |-t7 = tuple((1,))
+   25 |+t7 = (1,)
+26 26 | t8 = tuple([1,])
+
+C409.py:26:6: C409 [*] Unnecessary `list` literal passed to `tuple()` (rewrite as a `tuple` literal)
+   |
+24 | t6 = tuple([1])
+25 | t7 = tuple((1,))
+26 | t8 = tuple([1,])
+   |      ^^^^^^^^^^^ C409
+   |
+   = help: Rewrite as a `tuple` literal
 
+ℹ Unsafe fix
+23 23 | 
+24 24 | t6 = tuple([1])
+25 25 | t7 = tuple((1,))
+26    |-t8 = tuple([1,])
+   26 |+t8 = (1,)