Automatically fix a variety of comprehension rules (#553)

README.md

@@ -392,17 +392,17 @@ The 🛠 emoji indicates that a rule is automatically fixable by the `--fix` com
 
 | Code | Name | Message | Fix |
 | ---- | ---- | ------- | --- |
-| C400 | UnnecessaryGeneratorList | Unnecessary generator (rewrite as a `list` comprehension) |  |
-| C401 | UnnecessaryGeneratorSet | Unnecessary generator (rewrite as a `set` comprehension) |  |
+| C400 | UnnecessaryGeneratorList | Unnecessary generator (rewrite as a `list` comprehension) | 🛠 |
+| C401 | UnnecessaryGeneratorSet | Unnecessary generator (rewrite as a `set` comprehension) | 🛠 |
 | C402 | UnnecessaryGeneratorDict | Unnecessary generator (rewrite as a `dict` comprehension) |  |
-| C403 | UnnecessaryListComprehensionSet | Unnecessary `list` comprehension (rewrite as a `set` comprehension) |  |
+| C403 | UnnecessaryListComprehensionSet | Unnecessary `list` comprehension (rewrite as a `set` comprehension) | 🛠 |
 | C404 | UnnecessaryListComprehensionDict | Unnecessary `list` comprehension (rewrite as a `dict` comprehension) |  |
-| C405 | UnnecessaryLiteralSet | Unnecessary `(list\|tuple)` literal (rewrite as a `set` literal) |  |
+| C405 | UnnecessaryLiteralSet | Unnecessary `(list\|tuple)` literal (rewrite as a `set` literal) | 🛠 |
 | C406 | UnnecessaryLiteralDict | Unnecessary `(list\|tuple)` literal (rewrite as a `dict` literal) |  |
-| C408 | UnnecessaryCollectionCall | Unnecessary `(dict\|list\|tuple)` call (rewrite as a literal) |  |
+| C408 | UnnecessaryCollectionCall | Unnecessary `(dict\|list\|tuple)` call (rewrite as a literal) | 🛠 |
 | C409 | UnnecessaryLiteralWithinTupleCall | Unnecessary `(list\|tuple)` literal passed to `tuple()` (remove the outer call to `tuple()`) |  |
 | C410 | UnnecessaryLiteralWithinListCall | Unnecessary `(list\|tuple)` literal passed to `list()` (rewrite as a `list` literal) |  |
-| C411 | UnnecessaryListCall | Unnecessary `list` call (remove the outer call to `list()`) |  |
+| C411 | UnnecessaryListCall | Unnecessary `list` call (remove the outer call to `list()`) | 🛠 |
 | C413 | UnnecessaryCallAroundSorted | Unnecessary `(list\|reversed)` call around `sorted()` |  |
 | C414 | UnnecessaryDoubleCastOrProcess | Unnecessary `(list\|reversed\|set\|sorted\|tuple)` call within `(list\|set\|sorted\|tuple)()` |  |
 | C415 | UnnecessarySubscriptReversal | Unnecessary subscript reversal of iterable within `(reversed\|set\|sorted)()` |  |
@@ -521,7 +521,7 @@ including:
 - [`flake8-quotes`](https://pypi.org/project/flake8-quotes/)
 - [`flake8-comprehensions`](https://pypi.org/project/flake8-comprehensions/)
 - [`flake8-bugbear`](https://pypi.org/project/flake8-bugbear/) (10/32)
-- [`pyupgrade`](https://pypi.org/project/pyupgrade/) (8/34)
+- [`pyupgrade`](https://pypi.org/project/pyupgrade/) (9/34)
 - [`autoflake`](https://pypi.org/project/autoflake/) (1/7)
 
 Beyond rule-set parity, Ruff suffers from the following limitations vis-à-vis Flake8:
@@ -545,7 +545,7 @@ Today, Ruff can be used to replace Flake8 when used with any of the following pl
 - [`flake8-bugbear`](https://pypi.org/project/flake8-bugbear/) (10/32)
 
 Ruff also implements the functionality that you get from [`yesqa`](https://github.com/asottile/yesqa),
-and a subset of the rules implemented in [`pyupgrade`](https://pypi.org/project/pyupgrade/) (8/34).
+and a subset of the rules implemented in [`pyupgrade`](https://pypi.org/project/pyupgrade/) (9/34).
 
 If you're looking to use Ruff, but rely on an unsupported Flake8 plugin, free to file an Issue.
 

src/check_ast.rs

@@ -989,7 +989,12 @@ where
                 // flake8-comprehensions
                 if self.settings.enabled.contains(&CheckCode::C400) {
                     if let Some(check) = flake8_comprehensions::checks::unnecessary_generator_list(
-                        expr, func, args, keywords,
+                        expr,
+                        func,
+                        args,
+                        keywords,
+                        self.locator,
+                        self.patch(),
                     ) {
                         self.checks.push(check);
                     };
@@ -997,7 +1002,12 @@ where
 
                 if self.settings.enabled.contains(&CheckCode::C401) {
                     if let Some(check) = flake8_comprehensions::checks::unnecessary_generator_set(
-                        expr, func, args, keywords,
+                        expr,
+                        func,
+                        args,
+                        keywords,
+                        self.locator,
+                        self.patch(),
                     ) {
                         self.checks.push(check);
                     };
@@ -1014,7 +1024,12 @@ where
                 if self.settings.enabled.contains(&CheckCode::C403) {
                     if let Some(check) =
                         flake8_comprehensions::checks::unnecessary_list_comprehension_set(
-                            expr, func, args, keywords,
+                            expr,
+                            func,
+                            args,
+                            keywords,
+                            self.locator,
+                            self.patch(),
                         )
                     {
                         self.checks.push(check);
@@ -1033,7 +1048,12 @@ where
 
                 if self.settings.enabled.contains(&CheckCode::C405) {
                     if let Some(check) = flake8_comprehensions::checks::unnecessary_literal_set(
-                        expr, func, args, keywords,
+                        expr,
+                        func,
+                        args,
+                        keywords,
+                        self.locator,
+                        self.patch(),
                     ) {
                         self.checks.push(check);
                     };
@@ -1049,7 +1069,12 @@ where
 
                 if self.settings.enabled.contains(&CheckCode::C408) {
                     if let Some(check) = flake8_comprehensions::checks::unnecessary_collection_call(
-                        expr, func, args, keywords,
+                        expr,
+                        func,
+                        args,
+                        keywords,
+                        self.locator,
+                        self.patch(),
                     ) {
                         self.checks.push(check);
                     };
@@ -1076,9 +1101,13 @@ where
                 }
 
                 if self.settings.enabled.contains(&CheckCode::C411) {
-                    if let Some(check) =
-                        flake8_comprehensions::checks::unnecessary_list_call(expr, func, args)
-                    {
+                    if let Some(check) = flake8_comprehensions::checks::unnecessary_list_call(
+                        expr,
+                        func,
+                        args,
+                        self.locator,
+                        self.patch(),
+                    ) {
                         self.checks.push(check);
                     };
                 }

src/checks.rs

@@ -1469,6 +1469,12 @@ impl CheckKind {
                 | CheckKind::SuperCallWithParameters
                 | CheckKind::TypeOfPrimitive(_)
                 | CheckKind::UnnecessaryAbspath
+                | CheckKind::UnnecessaryCollectionCall(_)
+                | CheckKind::UnnecessaryGeneratorList
+                | CheckKind::UnnecessaryGeneratorSet
+                | CheckKind::UnnecessaryListCall
+                | CheckKind::UnnecessaryListComprehensionSet
+                | CheckKind::UnnecessaryLiteralSet(_)
                 | CheckKind::UnusedImport(_, false)
                 | CheckKind::UnusedLoopControlVariable(_)
                 | CheckKind::UnusedNOQA(_)

src/flake8_comprehensions/checks.rs

@@ -1,3 +1,4 @@
+use log::error;
 use num_bigint::BigInt;
 use rustpython_ast::{
     Comprehension, Constant, Expr, ExprKind, Keyword, KeywordData, Located, Unaryop,
@@ -5,6 +6,8 @@ use rustpython_ast::{
 
 use crate::ast::types::Range;
 use crate::checks::{Check, CheckKind};
+use crate::flake8_comprehensions::fixes;
+use crate::source_code_locator::SourceCodeLocator;
 
 fn function_name(func: &Expr) -> Option<&str> {
     if let ExprKind::Name { id, .. } = &func.node {
@@ -49,13 +52,22 @@ pub fn unnecessary_generator_list(
     func: &Expr,
     args: &[Expr],
     keywords: &[Keyword],
+    locator: &SourceCodeLocator,
+    fix: bool,
 ) -> Option<Check> {
     let argument = exactly_one_argument_with_matching_function("list", func, args, keywords)?;
     if let ExprKind::GeneratorExp { .. } = argument {
-        return Some(Check::new(
+        let mut check = Check::new(
             CheckKind::UnnecessaryGeneratorList,
             Range::from_located(expr),
-        ));
+        );
+        if fix {
+            match fixes::fix_unnecessary_generator_list(locator, expr) {
+                Ok(fix) => check.amend(fix),
+                Err(e) => error!("Failed to generate fix: {}", e),
+            }
+        }
+        return Some(check);
     }
     None
 }
@@ -66,13 +78,22 @@ pub fn unnecessary_generator_set(
     func: &Expr,
     args: &[Expr],
     keywords: &[Keyword],
+    locator: &SourceCodeLocator,
+    fix: bool,
 ) -> Option<Check> {
     let argument = exactly_one_argument_with_matching_function("set", func, args, keywords)?;
     if let ExprKind::GeneratorExp { .. } = argument {
-        return Some(Check::new(
+        let mut check = Check::new(
             CheckKind::UnnecessaryGeneratorSet,
             Range::from_located(expr),
-        ));
+        );
+        if fix {
+            match fixes::fix_unnecessary_generator_set(locator, expr) {
+                Ok(fix) => check.amend(fix),
+                Err(e) => error!("Failed to generate fix: {}", e),
+            }
+        }
+        return Some(check);
     }
     None
 }
@@ -105,13 +126,22 @@ pub fn unnecessary_list_comprehension_set(
     func: &Expr,
     args: &[Expr],
     keywords: &[Keyword],
+    locator: &SourceCodeLocator,
+    fix: bool,
 ) -> Option<Check> {
     let argument = exactly_one_argument_with_matching_function("set", func, args, keywords)?;
     if let ExprKind::ListComp { .. } = &argument {
-        return Some(Check::new(
+        let mut check = Check::new(
             CheckKind::UnnecessaryListComprehensionSet,
             Range::from_located(expr),
-        ));
+        );
+        if fix {
+            match fixes::fix_unnecessary_list_comprehension_set(locator, expr) {
+                Ok(fix) => check.amend(fix),
+                Err(e) => error!("Failed to generate fix: {}", e),
+            }
+        }
+        return Some(check);
     }
     None
 }
@@ -144,6 +174,8 @@ pub fn unnecessary_literal_set(
     func: &Expr,
     args: &[Expr],
     keywords: &[Keyword],
+    locator: &SourceCodeLocator,
+    fix: bool,
 ) -> Option<Check> {
     let argument = exactly_one_argument_with_matching_function("set", func, args, keywords)?;
     let kind = match argument {
@@ -151,10 +183,17 @@ pub fn unnecessary_literal_set(
         ExprKind::Tuple { .. } => "tuple",
         _ => return None,
     };
-    Some(Check::new(
+    let mut check = Check::new(
         CheckKind::UnnecessaryLiteralSet(kind.to_string()),
         Range::from_located(expr),
-    ))
+    );
+    if fix {
+        match fixes::fix_unnecessary_literal_set(locator, expr) {
+            Ok(fix) => check.amend(fix),
+            Err(e) => error!("Failed to generate fix: {}", e),
+        }
+    }
+    Some(check)
 }
 
 /// C406 (`dict([(1, 2)])`)
@@ -190,22 +229,36 @@ pub fn unnecessary_collection_call(
     func: &Expr,
     args: &[Expr],
     keywords: &[Located<KeywordData>],
+    locator: &SourceCodeLocator,
+    fix: bool,
 ) -> Option<Check> {
     if !args.is_empty() {
         return None;
     }
     let id = function_name(func)?;
     match id {
-        "dict" if keywords.is_empty() || keywords.iter().all(|kw| kw.node.arg.is_some()) => (),
+        "dict" if keywords.is_empty() || keywords.iter().all(|kw| kw.node.arg.is_some()) => {
+            // `dict()` or `dict(a=1)` (as opposed to `dict(**a)`)
+        }
         "list" | "tuple" => {
-            // list() or tuple()
+            // `list()` or `tuple()`
         }
         _ => return None,
     };
-    Some(Check::new(
+    let mut check = Check::new(
         CheckKind::UnnecessaryCollectionCall(id.to_string()),
         Range::from_located(expr),
-    ))
+    );
+    if fix {
+        // TODO(charlie): Support fixing `dict(a=1)`.
+        if keywords.is_empty() {
+            match fixes::fix_unnecessary_collection_call(locator, expr) {
+                Ok(fix) => check.amend(fix),
+                Err(e) => error!("Failed to generate fix: {}", e),
+            }
+        }
+    }
+    Some(check)
 }
 
 /// C409
@@ -245,13 +298,23 @@ pub fn unnecessary_literal_within_list_call(
 }
 
 /// C411
-pub fn unnecessary_list_call(expr: &Expr, func: &Expr, args: &[Expr]) -> Option<Check> {
+pub fn unnecessary_list_call(
+    expr: &Expr,
+    func: &Expr,
+    args: &[Expr],
+    locator: &SourceCodeLocator,
+    fix: bool,
+) -> Option<Check> {
     let argument = first_argument_with_matching_function("list", func, args)?;
     if let ExprKind::ListComp { .. } = argument {
-        return Some(Check::new(
-            CheckKind::UnnecessaryListCall,
-            Range::from_located(expr),
-        ));
+        let mut check = Check::new(CheckKind::UnnecessaryListCall, Range::from_located(expr));
+        if fix {
+            match fixes::fix_unnecessary_list_call(locator, expr) {
+                Ok(fix) => check.amend(fix),
+                Err(e) => error!("Failed to generate fix: {}", e),
+            }
+        }
+        return Some(check);
     }
     None
 }

src/flake8_comprehensions/fixes.rs

@@ -0,0 +1,397 @@
+use anyhow::Result;
+use libcst_native::{
+    Arg, Codegen, Dict, Expression, LeftCurlyBrace, LeftSquareBracket, List, ListComp,
+    RightCurlyBrace, RightSquareBracket, Set, SetComp, SmallStatement, Statement, Tuple,
+};
+use rustpython_ast::Expr;
+
+use crate::ast::types::Range;
+use crate::autofix::Fix;
+use crate::source_code_locator::SourceCodeLocator;
+
+/// (C400) Convert `list(x for x in y)` to `[x for x in y]`.
+pub fn fix_unnecessary_generator_list(locator: &SourceCodeLocator, expr: &Expr) -> Result<Fix> {
+    // Module(SimpleStatementLine(Expr(Call(GeneratorExp)))) ->
+    // Module(SimpleStatementLine(Expr(ListComp)))
+    let mut tree = match libcst_native::parse_module(
+        locator.slice_source_code_range(&Range::from_located(expr)),
+        None,
+    ) {
+        Ok(m) => m,
+        Err(_) => return Err(anyhow::anyhow!("Failed to extract CST from source.")),
+    };
+    let body = if let Some(Statement::Simple(body)) = tree.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Statement::Simple."));
+    };
+    let body = if let Some(SmallStatement::Expr(body)) = body.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!(
+            "Expected node to be: SmallStatement::Expr."
+        ));
+    };
+    let call = if let Expression::Call(call) = &mut body.value {
+        call
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Expression::Call."));
+    };
+    let arg = if let Some(Arg { value, .. }) = call.args.first_mut() {
+        value
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Arg."));
+    };
+    let generator_exp = if let Expression::GeneratorExp(generator_exp) = &arg {
+        generator_exp
+    } else {
+        return Err(anyhow::anyhow!(
+            "Expected node to be: Expression::GeneratorExp."
+        ));
+    };
+
+    body.value = Expression::ListComp(Box::new(ListComp {
+        elt: generator_exp.elt.clone(),
+        for_in: generator_exp.for_in.clone(),
+        lbracket: LeftSquareBracket {
+            whitespace_after: call.whitespace_before_args.clone(),
+        },
+        rbracket: RightSquareBracket {
+            whitespace_before: call.whitespace_after_func.clone(),
+        },
+        lpar: generator_exp.lpar.clone(),
+        rpar: generator_exp.rpar.clone(),
+    }));
+
+    let mut state = Default::default();
+    tree.codegen(&mut state);
+
+    Ok(Fix::replacement(
+        state.to_string(),
+        expr.location,
+        expr.end_location.unwrap(),
+    ))
+}
+
+/// (C401) Convert `set(x for x in y)` to `{x for x in y}`.
+pub fn fix_unnecessary_generator_set(locator: &SourceCodeLocator, expr: &Expr) -> Result<Fix> {
+    // Module(SimpleStatementLine(Expr(Call(GeneratorExp)))) ->
+    // Module(SimpleStatementLine(Expr(SetComp)))
+    let mut tree = match libcst_native::parse_module(
+        locator.slice_source_code_range(&Range::from_located(expr)),
+        None,
+    ) {
+        Ok(m) => m,
+        Err(_) => return Err(anyhow::anyhow!("Failed to extract CST from source.")),
+    };
+    let body = if let Some(Statement::Simple(body)) = tree.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Statement::Simple."));
+    };
+    let body = if let Some(SmallStatement::Expr(body)) = body.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!(
+            "Expected node to be: SmallStatement::Expr."
+        ));
+    };
+    let call = if let Expression::Call(call) = &mut body.value {
+        call
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Expression::Call."));
+    };
+    let arg = if let Some(Arg { value, .. }) = call.args.first_mut() {
+        value
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Arg."));
+    };
+    let generator_exp = if let Expression::GeneratorExp(generator_exp) = &arg {
+        generator_exp
+    } else {
+        return Err(anyhow::anyhow!(
+            "Expected node to be: Expression::GeneratorExp."
+        ));
+    };
+
+    body.value = Expression::SetComp(Box::new(SetComp {
+        elt: generator_exp.elt.clone(),
+        for_in: generator_exp.for_in.clone(),
+        lbrace: LeftCurlyBrace {
+            whitespace_after: call.whitespace_before_args.clone(),
+        },
+        rbrace: RightCurlyBrace {
+            whitespace_before: call.whitespace_after_func.clone(),
+        },
+        lpar: generator_exp.lpar.clone(),
+        rpar: generator_exp.rpar.clone(),
+    }));
+
+    let mut state = Default::default();
+    tree.codegen(&mut state);
+
+    Ok(Fix::replacement(
+        state.to_string(),
+        expr.location,
+        expr.end_location.unwrap(),
+    ))
+}
+
+/// (C403) Convert `set([x for x in y])` to `{x for x in y}`.
+pub fn fix_unnecessary_list_comprehension_set(
+    locator: &SourceCodeLocator,
+    expr: &Expr,
+) -> Result<Fix> {
+    // Module(SimpleStatementLine(Expr(Call(ListComp)))) ->
+    // Module(SimpleStatementLine(Expr(SetComp)))
+    let mut tree = match libcst_native::parse_module(
+        locator.slice_source_code_range(&Range::from_located(expr)),
+        None,
+    ) {
+        Ok(m) => m,
+        Err(_) => return Err(anyhow::anyhow!("Failed to extract CST from source.")),
+    };
+    let body = if let Some(Statement::Simple(body)) = tree.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Statement::Simple."));
+    };
+    let body = if let Some(SmallStatement::Expr(body)) = body.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!(
+            "Expected node to be: SmallStatement::Expr."
+        ));
+    };
+    let call = if let Expression::Call(call) = &mut body.value {
+        call
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Expression::Call."));
+    };
+    let arg = if let Some(Arg { value, .. }) = call.args.first_mut() {
+        value
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Arg."));
+    };
+    let list_comp = if let Expression::ListComp(list_comp) = arg {
+        list_comp
+    } else {
+        return Err(anyhow::anyhow!(
+            "Expected node to be: Expression::ListComp."
+        ));
+    };
+
+    body.value = Expression::SetComp(Box::new(SetComp {
+        elt: list_comp.elt.clone(),
+        for_in: list_comp.for_in.clone(),
+        lbrace: LeftCurlyBrace {
+            whitespace_after: call.whitespace_before_args.clone(),
+        },
+        rbrace: RightCurlyBrace {
+            whitespace_before: call.whitespace_after_func.clone(),
+        },
+        lpar: list_comp.lpar.clone(),
+        rpar: list_comp.rpar.clone(),
+    }));
+
+    let mut state = Default::default();
+    tree.codegen(&mut state);
+
+    Ok(Fix::replacement(
+        state.to_string(),
+        expr.location,
+        expr.end_location.unwrap(),
+    ))
+}
+
+/// (C405) Convert `set((1, 2))` to `{1, 2}`.
+pub fn fix_unnecessary_literal_set(locator: &SourceCodeLocator, expr: &Expr) -> Result<Fix> {
+    // Module(SimpleStatementLine(Expr(Call(List|Tuple)))) ->
+    // Module(SimpleStatementLine(Expr(Set)))
+    let mut tree = match libcst_native::parse_module(
+        locator.slice_source_code_range(&Range::from_located(expr)),
+        None,
+    ) {
+        Ok(m) => m,
+        Err(_) => return Err(anyhow::anyhow!("Failed to extract CST from source.")),
+    };
+    let body = if let Some(Statement::Simple(body)) = tree.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Statement::Simple."));
+    };
+    let body = if let Some(SmallStatement::Expr(body)) = body.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!(
+            "Expected node to be: SmallStatement::Expr."
+        ));
+    };
+    let call = if let Expression::Call(call) = &mut body.value {
+        call
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Expression::Call."));
+    };
+    let arg = if let Some(Arg { value, .. }) = call.args.first_mut() {
+        value
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Arg."));
+    };
+    let elements = match arg {
+        Expression::Tuple(inner) => inner.elements.clone(),
+        Expression::List(inner) => inner.elements.clone(),
+        _ => {
+            return Err(anyhow::anyhow!(
+                "Expected node to be: Expression::Tuple | Expression::List."
+            ))
+        }
+    };
+
+    if elements.is_empty() {
+        call.args = vec![];
+    } else {
+        body.value = Expression::Set(Box::new(Set {
+            elements,
+            lbrace: LeftCurlyBrace {
+                whitespace_after: call.whitespace_before_args.clone(),
+            },
+            rbrace: RightCurlyBrace {
+                whitespace_before: call.whitespace_after_func.clone(),
+            },
+            lpar: Default::default(),
+            rpar: Default::default(),
+        }));
+    }
+
+    let mut state = Default::default();
+    tree.codegen(&mut state);
+
+    Ok(Fix::replacement(
+        state.to_string(),
+        expr.location,
+        expr.end_location.unwrap(),
+    ))
+}
+
+/// (C408)
+pub fn fix_unnecessary_collection_call(locator: &SourceCodeLocator, expr: &Expr) -> Result<Fix> {
+    // Module(SimpleStatementLine(Expr(Call("list" | "tuple" | "dict")))) ->
+    // Module(SimpleStatementLine(Expr(List|Tuple|Dict)))
+    let mut tree = match libcst_native::parse_module(
+        locator.slice_source_code_range(&Range::from_located(expr)),
+        None,
+    ) {
+        Ok(m) => m,
+        Err(_) => return Err(anyhow::anyhow!("Failed to extract CST from source.")),
+    };
+    let body = if let Some(Statement::Simple(body)) = tree.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Statement::Simple."));
+    };
+    let body = if let Some(SmallStatement::Expr(body)) = body.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!(
+            "Expected node to be: SmallStatement::Expr."
+        ));
+    };
+    let call = if let Expression::Call(call) = &body.value {
+        call
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Expression::Call."));
+    };
+    let name = if let Expression::Name(name) = &call.func.as_ref() {
+        name
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Expression::Name."));
+    };
+
+    match name.value {
+        "tuple" => {
+            body.value = Expression::Tuple(Box::new(Tuple {
+                elements: vec![],
+                lpar: vec![Default::default()],
+                rpar: vec![Default::default()],
+            }));
+        }
+        "list" => {
+            body.value = Expression::List(Box::new(List {
+                elements: vec![],
+                lbracket: Default::default(),
+                rbracket: Default::default(),
+                lpar: vec![],
+                rpar: vec![],
+            }));
+        }
+        "dict" => {
+            body.value = Expression::Dict(Box::new(Dict {
+                elements: vec![],
+                lbrace: Default::default(),
+                rbrace: Default::default(),
+                lpar: vec![],
+                rpar: vec![],
+            }));
+        }
+        _ => {
+            return Err(anyhow::anyhow!("Expected function name to be one of: \
+                                        'tuple', 'list', 'dict'."
+                .to_string()));
+        }
+    };
+
+    let mut state = Default::default();
+    tree.codegen(&mut state);
+
+    Ok(Fix::replacement(
+        state.to_string(),
+        expr.location,
+        expr.end_location.unwrap(),
+    ))
+}
+
+/// (C411) Convert `list([i for i in x])` to `[i for i in x]`.
+pub fn fix_unnecessary_list_call(locator: &SourceCodeLocator, expr: &Expr) -> Result<Fix> {
+    // Module(SimpleStatementLine(Expr(Call(List|Tuple)))) ->
+    // Module(SimpleStatementLine(Expr(List|Tuple)))
+    let mut tree = match libcst_native::parse_module(
+        locator.slice_source_code_range(&Range::from_located(expr)),
+        None,
+    ) {
+        Ok(m) => m,
+        Err(_) => return Err(anyhow::anyhow!("Failed to extract CST from source.")),
+    };
+    let body = if let Some(Statement::Simple(body)) = tree.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Statement::Simple."));
+    };
+    let body = if let Some(SmallStatement::Expr(body)) = body.body.first_mut() {
+        body
+    } else {
+        return Err(anyhow::anyhow!(
+            "Expected node to be: SmallStatement::Expr."
+        ));
+    };
+    let call = if let Expression::Call(call) = &mut body.value {
+        call
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Expression::Call."));
+    };
+    let arg = if let Some(Arg { value, .. }) = call.args.first_mut() {
+        value
+    } else {
+        return Err(anyhow::anyhow!("Expected node to be: Arg."));
+    };
+
+    body.value = arg.clone();
+
+    let mut state = Default::default();
+    tree.codegen(&mut state);
+
+    Ok(Fix::replacement(
+        state.to_string(),
+        expr.location,
+        expr.end_location.unwrap(),
+    ))
+}

src/flake8_comprehensions/mod.rs

@@ -1 +1,2 @@
 pub mod checks;
+mod fixes;

src/snapshots/ruff__linter__tests__C400_C400.py.snap

@@ -9,5 +9,14 @@ expression: checks
   end_location:
     row: 1
     column: 29
-  fix: ~
+  fix:
+    patch:
+      content: "[x for x in range(3)]"
+      location:
+        row: 1
+        column: 4
+      end_location:
+        row: 1
+        column: 29
+    applied: false
 

src/snapshots/ruff__linter__tests__C401_C401.py.snap

@@ -9,5 +9,14 @@ expression: checks
   end_location:
     row: 1
     column: 28
-  fix: ~
+  fix:
+    patch:
+      content: "{x for x in range(3)}"
+      location:
+        row: 1
+        column: 4
+      end_location:
+        row: 1
+        column: 28
+    applied: false
 

src/snapshots/ruff__linter__tests__C403_C403.py.snap

@@ -9,5 +9,14 @@ expression: checks
   end_location:
     row: 1
     column: 30
-  fix: ~
+  fix:
+    patch:
+      content: "{x for x in range(3)}"
+      location:
+        row: 1
+        column: 4
+      end_location:
+        row: 1
+        column: 30
+    applied: false
 

src/snapshots/ruff__linter__tests__C405_C405.py.snap

@@ -10,7 +10,16 @@ expression: checks
   end_location:
     row: 1
     column: 16
-  fix: ~
+  fix:
+    patch:
+      content: "{1, 2}"
+      location:
+        row: 1
+        column: 5
+      end_location:
+        row: 1
+        column: 16
+    applied: false
 - kind:
     UnnecessaryLiteralSet: tuple
   location:
@@ -19,7 +28,16 @@ expression: checks
   end_location:
     row: 2
     column: 16
-  fix: ~
+  fix:
+    patch:
+      content: "{1, 2}"
+      location:
+        row: 2
+        column: 5
+      end_location:
+        row: 2
+        column: 16
+    applied: false
 - kind:
     UnnecessaryLiteralSet: list
   location:
@@ -28,7 +46,16 @@ expression: checks
   end_location:
     row: 3
     column: 12
-  fix: ~
+  fix:
+    patch:
+      content: set()
+      location:
+        row: 3
+        column: 5
+      end_location:
+        row: 3
+        column: 12
+    applied: false
 - kind:
     UnnecessaryLiteralSet: tuple
   location:
@@ -37,5 +64,14 @@ expression: checks
   end_location:
     row: 4
     column: 12
-  fix: ~
+  fix:
+    patch:
+      content: set()
+      location:
+        row: 4
+        column: 5
+      end_location:
+        row: 4
+        column: 12
+    applied: false
 

src/snapshots/ruff__linter__tests__C408_C408.py.snap

@@ -10,7 +10,16 @@ expression: checks
   end_location:
     row: 1
     column: 11
-  fix: ~
+  fix:
+    patch:
+      content: ()
+      location:
+        row: 1
+        column: 4
+      end_location:
+        row: 1
+        column: 11
+    applied: false
 - kind:
     UnnecessaryCollectionCall: list
   location:
@@ -19,7 +28,16 @@ expression: checks
   end_location:
     row: 2
     column: 10
-  fix: ~
+  fix:
+    patch:
+      content: "[]"
+      location:
+        row: 2
+        column: 4
+      end_location:
+        row: 2
+        column: 10
+    applied: false
 - kind:
     UnnecessaryCollectionCall: dict
   location:
@@ -28,7 +46,16 @@ expression: checks
   end_location:
     row: 3
     column: 11
-  fix: ~
+  fix:
+    patch:
+      content: "{}"
+      location:
+        row: 3
+        column: 5
+      end_location:
+        row: 3
+        column: 11
+    applied: false
 - kind:
     UnnecessaryCollectionCall: dict
   location:

src/snapshots/ruff__linter__tests__C411_C411.py.snap

@@ -9,5 +9,14 @@ expression: checks
   end_location:
     row: 2
     column: 20
-  fix: ~
+  fix:
+    patch:
+      content: "[i for i in x]"
+      location:
+        row: 2
+        column: 0
+      end_location:
+        row: 2
+        column: 20
+    applied: false