[flake8-comprehensions] Handle trailing comma in fixes for unnecessary-generator-list/set (C400,C401) (#15929)

The unsafe fixes for the rules [unnecessary-generator-list
(C400)](https://docs.astral.sh/ruff/rules/unnecessary-generator-list/#unnecessary-generator-list-c400)
and [unnecessary-generator-set
(C401)](https://docs.astral.sh/ruff/rules/unnecessary-generator-set/#unnecessary-generator-set-c401)
used to introduce syntax errors if the argument to `list` or `set` had a
trailing comma, because the fix would retain the comma after
transforming the function call to a comprehension.

This PR accounts for the trailing comma when replacing the end of the
call with a `]` or `}`.

Closes #15852

crates/ruff_linter/resources/test/fixtures/flake8_comprehensions/C400.py

@@ -16,6 +16,17 @@ list((2 * x for x in range(3)))
 list(((2 * x for x in range(3))))
 list((((2 * x for x in range(3)))))
 
+# Account for trailing comma in fix
+# See https://github.com/astral-sh/ruff/issues/15852
+list((0 for _ in []),)
+list(
+     (0 for _ in [])
+     # some comments
+     ,
+     # some more
+ )
+
+
 # Not built-in list.
 def list(*args, **kwargs):
     return None

crates/ruff_linter/resources/test/fixtures/flake8_comprehensions/C401.py

@@ -26,6 +26,16 @@ set((2 * x for x in range(3)))
 set(((2 * x for x in range(3))))
 set((((2 * x for x in range(3)))))
 
+# Account for trailing comma in fix
+# See https://github.com/astral-sh/ruff/issues/15852
+set((0 for _ in []),)
+set(
+    (0 for _ in [])
+    # some comments
+    ,
+    # some more
+)
+
 # Not built-in set.
 def set(*args, **kwargs):
     return None

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

@@ -4,7 +4,8 @@ use ruff_python_ast as ast;
 use ruff_python_ast::comparable::ComparableExpr;
 use ruff_python_ast::parenthesize::parenthesized_range;
 use ruff_python_ast::ExprGenerator;
-use ruff_text_size::{Ranged, TextSize};
+use ruff_python_trivia::{SimpleTokenKind, SimpleTokenizer};
+use ruff_text_size::{Ranged, TextRange, TextSize};
 
 use crate::checkers::ast::Checker;
 
@@ -123,11 +124,14 @@ pub(crate) fn unnecessary_generator_list(checker: &mut Checker, call: &ast::Expr
         );
 
         // Replace `)` with `]`.
-        let call_end = Edit::replacement(
+        // Place `]` at argument's end or at trailing comma if present
-            "]".to_string(),
+        let mut tokenizer =
-            call.arguments.end() - TextSize::from(1),
+            SimpleTokenizer::new(checker.source(), TextRange::new(argument.end(), call.end()));
-            call.end(),
+        let right_bracket_loc = tokenizer
-        );
+            .find(|token| token.kind == SimpleTokenKind::Comma)
+            .map_or(call.arguments.end(), |comma| comma.end())
+            - TextSize::from(1);
+        let call_end = Edit::replacement("]".to_string(), right_bracket_loc, call.end());
 
         // Remove the inner parentheses, if the expression is a generator. The easiest way to do
         // this reliably is to use the printer.

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

@@ -4,7 +4,8 @@ use ruff_python_ast as ast;
 use ruff_python_ast::comparable::ComparableExpr;
 use ruff_python_ast::parenthesize::parenthesized_range;
 use ruff_python_ast::ExprGenerator;
-use ruff_text_size::{Ranged, TextSize};
+use ruff_python_trivia::{SimpleTokenKind, SimpleTokenizer};
+use ruff_text_size::{Ranged, TextRange, TextSize};
 
 use crate::checkers::ast::Checker;
 use crate::rules::flake8_comprehensions::fixes::{pad_end, pad_start};
@@ -126,9 +127,16 @@ pub(crate) fn unnecessary_generator_set(checker: &mut Checker, call: &ast::ExprC
         );
 
         // Replace `)` with `}`.
+        // Place `}` at argument's end or at trailing comma if present
+        let mut tokenizer =
+            SimpleTokenizer::new(checker.source(), TextRange::new(argument.end(), call.end()));
+        let right_brace_loc = tokenizer
+            .find(|token| token.kind == SimpleTokenKind::Comma)
+            .map_or(call.arguments.end(), |comma| comma.end())
+            - TextSize::from(1);
         let call_end = Edit::replacement(
             pad_end("}", call.range(), checker.locator(), checker.semantic()),
-            call.arguments.end() - TextSize::from(1),
+            right_brace_loc,
             call.end(),
         );
 

crates/ruff_linter/src/rules/flake8_comprehensions/snapshots/ruff_linter__rules__flake8_comprehensions__tests__C400_C400.py.snap

@@ -127,7 +127,7 @@ C400.py:16:1: C400 [*] Unnecessary generator (rewrite as a list comprehension)
    16 |+[2 * x for x in range(3)]
 17 17 | list((((2 * x for x in range(3)))))
 18 18 | 
-19 19 | # Not built-in list.
+19 19 | # Account for trailing comma in fix
 
 C400.py:17:1: C400 [*] Unnecessary generator (rewrite as a list comprehension)
    |
@@ -136,7 +136,7 @@ C400.py:17:1: C400 [*] Unnecessary generator (rewrite as a list comprehension)
 17 | list((((2 * x for x in range(3)))))
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ C400
 18 |
-19 | # Not built-in list.
+19 | # Account for trailing comma in fix
    |
    = help: Rewrite as a list comprehension
 
@@ -147,5 +147,57 @@ C400.py:17:1: C400 [*] Unnecessary generator (rewrite as a list comprehension)
 17    |-list((((2 * x for x in range(3)))))
    17 |+[2 * x for x in range(3)]
 18 18 | 
-19 19 | # Not built-in list.
+19 19 | # Account for trailing comma in fix
-20 20 | def list(*args, **kwargs):
+20 20 | # See https://github.com/astral-sh/ruff/issues/15852
+
+C400.py:21:1: C400 [*] Unnecessary generator (rewrite as a list comprehension)
+   |
+19 | # Account for trailing comma in fix
+20 | # See https://github.com/astral-sh/ruff/issues/15852
+21 | list((0 for _ in []),)
+   | ^^^^^^^^^^^^^^^^^^^^^^ C400
+22 | list(
+23 |      (0 for _ in [])
+   |
+   = help: Rewrite as a list comprehension
+
+ℹ Unsafe fix
+18 18 | 
+19 19 | # Account for trailing comma in fix
+20 20 | # See https://github.com/astral-sh/ruff/issues/15852
+21    |-list((0 for _ in []),)
+   21 |+[0 for _ in []]
+22 22 | list(
+23 23 |      (0 for _ in [])
+24 24 |      # some comments
+
+C400.py:22:1: C400 [*] Unnecessary generator (rewrite as a list comprehension)
+   |
+20 |   # See https://github.com/astral-sh/ruff/issues/15852
+21 |   list((0 for _ in []),)
+22 | / list(
+23 | |      (0 for _ in [])
+24 | |      # some comments
+25 | |      ,
+26 | |      # some more
+27 | |  )
+   | |__^ C400
+   |
+   = help: Rewrite as a list comprehension
+
+ℹ Unsafe fix
+19 19 | # Account for trailing comma in fix
+20 20 | # See https://github.com/astral-sh/ruff/issues/15852
+21 21 | list((0 for _ in []),)
+22    |-list(
+23    |-     (0 for _ in [])
+   22 |+[
+   23 |+     0 for _ in []
+24 24 |      # some comments
+25    |-     ,
+26    |-     # some more
+27    |- )
+   25 |+     ]
+28 26 | 
+29 27 | 
+30 28 | # Not built-in list.

crates/ruff_linter/src/rules/flake8_comprehensions/snapshots/ruff_linter__rules__flake8_comprehensions__tests__C401_C401.py.snap

@@ -290,7 +290,7 @@ C401.py:26:1: C401 [*] Unnecessary generator (rewrite as a set comprehension)
    26 |+{2 * x for x in range(3)}
 27 27 | set((((2 * x for x in range(3)))))
 28 28 | 
-29 29 | # Not built-in set.
+29 29 | # Account for trailing comma in fix
 
 C401.py:27:1: C401 [*] Unnecessary generator (rewrite as a set comprehension)
    |
@@ -299,7 +299,7 @@ C401.py:27:1: C401 [*] Unnecessary generator (rewrite as a set comprehension)
 27 | set((((2 * x for x in range(3)))))
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ C401
 28 |
-29 | # Not built-in set.
+29 | # Account for trailing comma in fix
    |
    = help: Rewrite as a set comprehension
 
@@ -310,5 +310,59 @@ C401.py:27:1: C401 [*] Unnecessary generator (rewrite as a set comprehension)
 27    |-set((((2 * x for x in range(3)))))
    27 |+{2 * x for x in range(3)}
 28 28 | 
-29 29 | # Not built-in set.
+29 29 | # Account for trailing comma in fix
-30 30 | def set(*args, **kwargs):
+30 30 | # See https://github.com/astral-sh/ruff/issues/15852
+
+C401.py:31:1: C401 [*] Unnecessary generator (rewrite as a set comprehension)
+   |
+29 | # Account for trailing comma in fix
+30 | # See https://github.com/astral-sh/ruff/issues/15852
+31 | set((0 for _ in []),)
+   | ^^^^^^^^^^^^^^^^^^^^^ C401
+32 | set(
+33 |     (0 for _ in [])
+   |
+   = help: Rewrite as a set comprehension
+
+ℹ Unsafe fix
+28 28 | 
+29 29 | # Account for trailing comma in fix
+30 30 | # See https://github.com/astral-sh/ruff/issues/15852
+31    |-set((0 for _ in []),)
+   31 |+{0 for _ in []}
+32 32 | set(
+33 33 |     (0 for _ in [])
+34 34 |     # some comments
+
+C401.py:32:1: C401 [*] Unnecessary generator (rewrite as a set comprehension)
+   |
+30 |   # See https://github.com/astral-sh/ruff/issues/15852
+31 |   set((0 for _ in []),)
+32 | / set(
+33 | |     (0 for _ in [])
+34 | |     # some comments
+35 | |     ,
+36 | |     # some more
+37 | | )
+   | |_^ C401
+38 |
+39 |   # Not built-in set.
+   |
+   = help: Rewrite as a set comprehension
+
+ℹ Unsafe fix
+29 29 | # Account for trailing comma in fix
+30 30 | # See https://github.com/astral-sh/ruff/issues/15852
+31 31 | set((0 for _ in []),)
+32    |-set(
+33    |-    (0 for _ in [])
+   32 |+{
+   33 |+    0 for _ in []
+34 34 |     # some comments
+35    |-    ,
+36    |-    # some more
+37    |-)
+   35 |+    }
+38 36 | 
+39 37 | # Not built-in set.
+40 38 | def set(*args, **kwargs):