Implicit flake8-implicit-str-concat (#1463)

LICENSE

@@ -388,6 +388,31 @@ are:
     SOFTWARE.
   """
 
+- flake8-implicit-str-concat, licensed as follows:
+  """
+    The MIT License (MIT)
+
+    Copyright (c) 2019 Dylan Turner
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+  """
+
 - flake8-import-conventions, licensed as follows:
   """
     MIT License

README.md

@@ -95,6 +95,7 @@ of [Conda](https://docs.conda.io/en/latest/):
    1. [flake8-comprehensions (C4)](#flake8-comprehensions-c4)
    1. [flake8-debugger (T10)](#flake8-debugger-t10)
    1. [flake8-errmsg (EM)](#flake8-errmsg-em)
+   1. [flake8-implicit-str-concat (ISC)](#flake8-implicit-str-concat-isc)
    1. [flake8-import-conventions (ICN)](#flake8-import-conventions-icn)
    1. [flake8-print (T20)](#flake8-print-t20)
    1. [flake8-quotes (Q)](#flake8-quotes-q)
@@ -854,6 +855,16 @@ For more, see [flake8-errmsg](https://pypi.org/project/flake8-errmsg/0.4.0/) on
 | EM102 | FStringInException | Exception must not use an f-string literal, assign to variable first |  |
 | EM103 | DotFormatInException | Exception must not use a `.format()` string directly, assign to variable first |  |
 
+### flake8-implicit-str-concat (ISC)
+
+For more, see [flake8-implicit-str-concat](https://pypi.org/project/flake8-implicit-str-concat/0.3.0/) on PyPI.
+
+| Code | Name | Message | Fix |
+| ---- | ---- | ------- | --- |
+| ISC001 | SingleLineImplicitStringConcatenation | Implicitly concatenated string literals on one line |  |
+| ISC002 | MultiLineImplicitStringConcatenation | Implicitly concatenated string literals over continuation line |  |
+| ISC003 | ExplicitStringConcatenation | Explicitly concatenated string should be implicitly concatenated |  |
+
 ### flake8-import-conventions (ICN)
 
 | Code | Name | Message | Fix |
@@ -1274,6 +1285,7 @@ natively, including:
 - [`flake8-docstrings`](https://pypi.org/project/flake8-docstrings/)
 - [`flake8-eradicate`](https://pypi.org/project/flake8-eradicate/)
 - [`flake8-errmsg`](https://pypi.org/project/flake8-errmsg/)
+- [`flake8-implicit-str-concat`](https://pypi.org/project/flake8-implicit-str-concat/)
 - [`flake8-import-conventions`](https://github.com/joaopalmeiro/flake8-import-conventions)
 - [`flake8-print`](https://pypi.org/project/flake8-print/)
 - [`flake8-quotes`](https://pypi.org/project/flake8-quotes/)
@@ -1330,6 +1342,7 @@ Today, Ruff can be used to replace Flake8 when used with any of the following pl
 - [`flake8-docstrings`](https://pypi.org/project/flake8-docstrings/)
 - [`flake8-eradicate`](https://pypi.org/project/flake8-eradicate/)
 - [`flake8-errmsg`](https://pypi.org/project/flake8-errmsg/)
+- [`flake8-implicit-str-concat`](https://pypi.org/project/flake8-implicit-str-concat/)
 - [`flake8-import-conventions`](https://github.com/joaopalmeiro/flake8-import-conventions)
 - [`flake8-print`](https://pypi.org/project/flake8-print/)
 - [`flake8-quotes`](https://pypi.org/project/flake8-quotes/)

flake8_to_ruff/src/plugin.rs

@@ -16,16 +16,17 @@ pub enum Plugin {
     Flake8Datetimez,
     Flake8Debugger,
     Flake8Docstrings,
-    Flake8ErrMsg,
     Flake8Eradicate,
+    Flake8ErrMsg,
+    Flake8ImplicitStrConcat,
     Flake8Print,
     Flake8Quotes,
     Flake8Return,
     Flake8Simplify,
     Flake8TidyImports,
     McCabe,
-    PandasVet,
     PEP8Naming,
+    PandasVet,
     Pyupgrade,
 }
 
@@ -45,6 +46,7 @@ impl FromStr for Plugin {
             "flake8-docstrings" => Ok(Plugin::Flake8Docstrings),
             "flake8-eradicate" => Ok(Plugin::Flake8Eradicate),
             "flake8-errmsg" => Ok(Plugin::Flake8ErrMsg),
+            "flake8-implicit-str-concat" => Ok(Plugin::Flake8ImplicitStrConcat),
             "flake8-print" => Ok(Plugin::Flake8Print),
             "flake8-quotes" => Ok(Plugin::Flake8Quotes),
             "flake8-return" => Ok(Plugin::Flake8Return),
@@ -76,14 +78,15 @@ impl fmt::Debug for Plugin {
                 Plugin::Flake8Docstrings => "flake8-docstrings",
                 Plugin::Flake8Eradicate => "flake8-eradicate",
                 Plugin::Flake8ErrMsg => "flake8-errmsg",
+                Plugin::Flake8ImplicitStrConcat => "flake8-implicit-str-concat",
                 Plugin::Flake8Print => "flake8-print",
                 Plugin::Flake8Quotes => "flake8-quotes",
                 Plugin::Flake8Return => "flake8-return",
                 Plugin::Flake8Simplify => "flake8-simplify",
                 Plugin::Flake8TidyImports => "flake8-tidy-imports",
                 Plugin::McCabe => "mccabe",
-                Plugin::PandasVet => "pandas-vet",
                 Plugin::PEP8Naming => "pep8-naming",
+                Plugin::PandasVet => "pandas-vet",
                 Plugin::Pyupgrade => "pyupgrade",
             }
         )
@@ -106,6 +109,7 @@ impl Plugin {
             // TODO(charlie): Handle rename of `E` to `ERA`.
             Plugin::Flake8Eradicate => CheckCodePrefix::ERA,
             Plugin::Flake8ErrMsg => CheckCodePrefix::EM,
+            Plugin::Flake8ImplicitStrConcat => CheckCodePrefix::ISC,
             Plugin::Flake8Print => CheckCodePrefix::T2,
             Plugin::Flake8Quotes => CheckCodePrefix::Q,
             Plugin::Flake8Return => CheckCodePrefix::RET,
@@ -146,6 +150,7 @@ impl Plugin {
             }
             Plugin::Flake8Eradicate => vec![CheckCodePrefix::ERA],
             Plugin::Flake8ErrMsg => vec![CheckCodePrefix::EM],
+            Plugin::Flake8ImplicitStrConcat => vec![CheckCodePrefix::ISC],
             Plugin::Flake8Print => vec![CheckCodePrefix::T2],
             Plugin::Flake8Quotes => vec![CheckCodePrefix::Q],
             Plugin::Flake8Return => vec![CheckCodePrefix::RET],
@@ -449,6 +454,7 @@ pub fn infer_plugins_from_codes(codes: &BTreeSet<CheckCodePrefix>) -> Vec<Plugin
         Plugin::Flake8Docstrings,
         Plugin::Flake8Eradicate,
         Plugin::Flake8ErrMsg,
+        Plugin::Flake8ImplicitStrConcat,
         Plugin::Flake8Print,
         Plugin::Flake8Quotes,
         Plugin::Flake8Return,

resources/test/fixtures/flake8_implicit_str_concat/ISC.py

@@ -0,0 +1,36 @@
+_ = "a" "b" "c"
+
+_ = "abc" + "def"
+
+_ = "abc" \
+    "def"
+
+_ = (
+  "abc" +
+  "def"
+)
+
+_ = (
+  f"abc" +
+  "def"
+)
+
+_ = (
+  b"abc" +
+  b"def"
+)
+
+_ = (
+  "abc"
+  "def"
+)
+
+_ = (
+  f"abc"
+  "def"
+)
+
+_ = (
+  b"abc"
+  b"def"
+)

ruff.schema.json

@@ -683,6 +683,12 @@
         "ICN0",
         "ICN00",
         "ICN001",
+        "ISC",
+        "ISC0",
+        "ISC00",
+        "ISC001",
+        "ISC002",
+        "ISC003",
         "M",
         "M0",
         "M001",

src/checkers/ast.rs

@@ -39,10 +39,10 @@ use crate::visibility::{module_visibility, transition_scope, Modifier, Visibilit
 use crate::{
     docstrings, flake8_2020, flake8_annotations, flake8_bandit, flake8_blind_except,
     flake8_boolean_trap, flake8_bugbear, flake8_builtins, flake8_comprehensions, flake8_datetimez,
-    flake8_debugger, flake8_errmsg, flake8_import_conventions, flake8_print, flake8_return,
+    flake8_debugger, flake8_errmsg, flake8_implicit_str_concat, flake8_import_conventions,
-    flake8_simplify, flake8_tidy_imports, flake8_unused_arguments, mccabe, noqa, pandas_vet,
+    flake8_print, flake8_return, flake8_simplify, flake8_tidy_imports, flake8_unused_arguments,
-    pep8_naming, pycodestyle, pydocstyle, pyflakes, pygrep_hooks, pylint, pyupgrade, ruff,
+    mccabe, noqa, pandas_vet, pep8_naming, pycodestyle, pydocstyle, pyflakes, pygrep_hooks, pylint,
-    visibility,
+    pyupgrade, ruff, visibility,
 };
 
 const GLOBAL_SCOPE_INDEX: usize = 0;
@@ -2271,6 +2271,15 @@ where
                     }
                 }
             }
+            ExprKind::BinOp {
+                op: Operator::Add, ..
+            } => {
+                if self.settings.enabled.contains(&CheckCode::ISC003) {
+                    if let Some(check) = flake8_implicit_str_concat::checks::explicit(expr) {
+                        self.add_check(check);
+                    }
+                }
+            }
             ExprKind::UnaryOp { op, operand } => {
                 let check_not_in = self.settings.enabled.contains(&CheckCode::E713);
                 let check_not_is = self.settings.enabled.contains(&CheckCode::E714);

src/checkers/tokens.rs

@@ -7,7 +7,7 @@ use crate::lex::docstring_detection::StateMachine;
 use crate::ruff::checks::Context;
 use crate::settings::flags;
 use crate::source_code_locator::SourceCodeLocator;
-use crate::{eradicate, flake8_quotes, pycodestyle, ruff, Settings};
+use crate::{eradicate, flake8_implicit_str_concat, flake8_quotes, pycodestyle, ruff, Settings};
 
 pub fn check_tokens(
     locator: &SourceCodeLocator,
@@ -26,6 +26,8 @@ pub fn check_tokens(
         || settings.enabled.contains(&CheckCode::Q003);
     let enforce_commented_out_code = settings.enabled.contains(&CheckCode::ERA001);
     let enforce_invalid_escape_sequence = settings.enabled.contains(&CheckCode::W605);
+    let enforce_implicit_string_concatenation = settings.enabled.contains(&CheckCode::ISC001)
+        || settings.enabled.contains(&CheckCode::ISC002);
 
     let mut state_machine = StateMachine::default();
     for &(start, ref tok, end) in tokens.iter().flatten() {
@@ -99,5 +101,14 @@ pub fn check_tokens(
         }
     }
 
+    // ISC001, ISC002
+    if enforce_implicit_string_concatenation {
+        checks.extend(
+            flake8_implicit_str_concat::checks::implicit(tokens, locator)
+                .into_iter()
+                .filter(|check| settings.enabled.contains(check.kind.code())),
+        );
+    }
+
     checks
 }

src/checks.rs

@@ -176,6 +176,10 @@ pub enum CheckCode {
     RET506,
     RET507,
     RET508,
+    // flake8-implicit-str-concat
+    ISC001,
+    ISC002,
+    ISC003,
     // flake8-print
     T201,
     T203,
@@ -377,6 +381,7 @@ pub enum CheckCategory {
     Flake8Comprehensions,
     Flake8Debugger,
     Flake8ErrMsg,
+    Flake8ImplicitStrConcat,
     Flake8ImportConventions,
     Flake8Print,
     Flake8Quotes,
@@ -420,6 +425,7 @@ impl CheckCategory {
             CheckCategory::Flake8Comprehensions => "flake8-comprehensions",
             CheckCategory::Flake8Debugger => "flake8-debugger",
             CheckCategory::Flake8ErrMsg => "flake8-errmsg",
+            CheckCategory::Flake8ImplicitStrConcat => "flake8-implicit-str-concat",
             CheckCategory::Flake8ImportConventions => "flake8-import-conventions",
             CheckCategory::Flake8Print => "flake8-print",
             CheckCategory::Flake8Quotes => "flake8-quotes",
@@ -453,19 +459,21 @@ impl CheckCategory {
             CheckCategory::Flake8Bugbear => vec![CheckCodePrefix::B],
             CheckCategory::Flake8Builtins => vec![CheckCodePrefix::A],
             CheckCategory::Flake8Comprehensions => vec![CheckCodePrefix::C4],
+            CheckCategory::Flake8Datetimez => vec![CheckCodePrefix::DTZ],
             CheckCategory::Flake8Debugger => vec![CheckCodePrefix::T10],
             CheckCategory::Flake8ErrMsg => vec![CheckCodePrefix::EM],
+            CheckCategory::Flake8ImplicitStrConcat => vec![CheckCodePrefix::ISC],
+            CheckCategory::Flake8ImportConventions => vec![CheckCodePrefix::ICN],
             CheckCategory::Flake8Print => vec![CheckCodePrefix::T20],
             CheckCategory::Flake8Quotes => vec![CheckCodePrefix::Q],
             CheckCategory::Flake8Return => vec![CheckCodePrefix::RET],
             CheckCategory::Flake8Simplify => vec![CheckCodePrefix::SIM],
             CheckCategory::Flake8TidyImports => vec![CheckCodePrefix::TID],
             CheckCategory::Flake8UnusedArguments => vec![CheckCodePrefix::ARG],
-            CheckCategory::Flake8Datetimez => vec![CheckCodePrefix::DTZ],
             CheckCategory::Isort => vec![CheckCodePrefix::I],
             CheckCategory::McCabe => vec![CheckCodePrefix::C90],
-            CheckCategory::PandasVet => vec![CheckCodePrefix::PD],
             CheckCategory::PEP8Naming => vec![CheckCodePrefix::N],
+            CheckCategory::PandasVet => vec![CheckCodePrefix::PD],
             CheckCategory::Pycodestyle => vec![CheckCodePrefix::E, CheckCodePrefix::W],
             CheckCategory::Pydocstyle => vec![CheckCodePrefix::D],
             CheckCategory::Pyflakes => vec![CheckCodePrefix::F],
@@ -477,7 +485,6 @@ impl CheckCategory {
                 CheckCodePrefix::PLW,
             ],
             CheckCategory::Pyupgrade => vec![CheckCodePrefix::UP],
-            CheckCategory::Flake8ImportConventions => vec![CheckCodePrefix::ICN],
             CheckCategory::Ruff => vec![CheckCodePrefix::RUF],
         }
     }
@@ -527,6 +534,10 @@ impl CheckCategory {
                 "https://pypi.org/project/flake8-errmsg/0.4.0/",
                 &Platform::PyPI,
             )),
+            CheckCategory::Flake8ImplicitStrConcat => Some((
+                "https://pypi.org/project/flake8-implicit-str-concat/0.3.0/",
+                &Platform::PyPI,
+            )),
             CheckCategory::Flake8ImportConventions => None,
             CheckCategory::Flake8Print => Some((
                 "https://pypi.org/project/flake8-print/5.0.0/",
@@ -796,6 +807,10 @@ pub enum CheckKind {
     SuperfluousElseRaise(Branch),
     SuperfluousElseContinue(Branch),
     SuperfluousElseBreak(Branch),
+    // flake8-implicit-str-concat
+    SingleLineImplicitStringConcatenation,
+    MultiLineImplicitStringConcatenation,
+    ExplicitStringConcatenation,
     // flake8-print
     PrintFound,
     PPrintFound,
@@ -992,6 +1007,8 @@ impl CheckCode {
             | CheckCode::PGH003
             | CheckCode::PGH004 => &LintSource::Lines,
             CheckCode::ERA001
+            | CheckCode::ISC001
+            | CheckCode::ISC002
             | CheckCode::Q000
             | CheckCode::Q001
             | CheckCode::Q002
@@ -1180,6 +1197,10 @@ impl CheckCode {
             CheckCode::RET506 => CheckKind::SuperfluousElseRaise(Branch::Else),
             CheckCode::RET507 => CheckKind::SuperfluousElseContinue(Branch::Else),
             CheckCode::RET508 => CheckKind::SuperfluousElseBreak(Branch::Else),
+            // flake8-implicit-str-concat
+            CheckCode::ISC001 => CheckKind::SingleLineImplicitStringConcatenation,
+            CheckCode::ISC002 => CheckKind::MultiLineImplicitStringConcatenation,
+            CheckCode::ISC003 => CheckKind::ExplicitStringConcatenation,
             // flake8-print
             CheckCode::T201 => CheckKind::PrintFound,
             CheckCode::T203 => CheckKind::PPrintFound,
@@ -1576,9 +1597,10 @@ impl CheckCode {
             CheckCode::FBT002 => CheckCategory::Flake8BooleanTrap,
             CheckCode::FBT003 => CheckCategory::Flake8BooleanTrap,
             CheckCode::I001 => CheckCategory::Isort,
-            CheckCode::TID251 => CheckCategory::Flake8TidyImports,
-            CheckCode::TID252 => CheckCategory::Flake8TidyImports,
             CheckCode::ICN001 => CheckCategory::Flake8ImportConventions,
+            CheckCode::ISC001 => CheckCategory::Flake8ImplicitStrConcat,
+            CheckCode::ISC002 => CheckCategory::Flake8ImplicitStrConcat,
+            CheckCode::ISC003 => CheckCategory::Flake8ImplicitStrConcat,
             CheckCode::N801 => CheckCategory::PEP8Naming,
             CheckCode::N802 => CheckCategory::PEP8Naming,
             CheckCode::N803 => CheckCategory::PEP8Naming,
@@ -1649,6 +1671,8 @@ impl CheckCode {
             CheckCode::T100 => CheckCategory::Flake8Debugger,
             CheckCode::T201 => CheckCategory::Flake8Print,
             CheckCode::T203 => CheckCategory::Flake8Print,
+            CheckCode::TID251 => CheckCategory::Flake8TidyImports,
+            CheckCode::TID252 => CheckCategory::Flake8TidyImports,
             CheckCode::UP001 => CheckCategory::Pyupgrade,
             CheckCode::UP003 => CheckCategory::Pyupgrade,
             CheckCode::UP004 => CheckCategory::Pyupgrade,
@@ -1834,6 +1858,10 @@ impl CheckKind {
             CheckKind::SuperfluousElseRaise(..) => &CheckCode::RET506,
             CheckKind::SuperfluousElseContinue(..) => &CheckCode::RET507,
             CheckKind::SuperfluousElseBreak(..) => &CheckCode::RET508,
+            // flake8-implicit-str-concat
+            CheckKind::SingleLineImplicitStringConcatenation => &CheckCode::ISC001,
+            CheckKind::MultiLineImplicitStringConcatenation => &CheckCode::ISC002,
+            CheckKind::ExplicitStringConcatenation => &CheckCode::ISC003,
             // flake8-print
             CheckKind::PrintFound => &CheckCode::T201,
             CheckKind::PPrintFound => &CheckCode::T203,
@@ -2484,6 +2512,16 @@ impl CheckKind {
             CheckKind::SuperfluousElseBreak(branch) => {
                 format!("Unnecessary `{branch}` after `break` statement")
             }
+            // flake8-implicit-str-concat
+            CheckKind::SingleLineImplicitStringConcatenation => {
+                "Implicitly concatenated string literals on one line".to_string()
+            }
+            CheckKind::MultiLineImplicitStringConcatenation => {
+                "Implicitly concatenated string literals over continuation line".to_string()
+            }
+            CheckKind::ExplicitStringConcatenation => {
+                "Explicitly concatenated string should be implicitly concatenated".to_string()
+            }
             // flake8-print
             CheckKind::PrintFound => "`print` found".to_string(),
             CheckKind::PPrintFound => "`pprint` found".to_string(),

src/checks_gen.rs

@@ -314,6 +314,12 @@ pub enum CheckCodePrefix {
     ICN0,
     ICN00,
     ICN001,
+    ISC,
+    ISC0,
+    ISC00,
+    ISC001,
+    ISC002,
+    ISC003,
     M,
     M0,
     M001,
@@ -717,6 +723,9 @@ impl CheckCodePrefix {
                 CheckCode::RET506,
                 CheckCode::RET507,
                 CheckCode::RET508,
+                CheckCode::ISC001,
+                CheckCode::ISC002,
+                CheckCode::ISC003,
                 CheckCode::T201,
                 CheckCode::T203,
                 CheckCode::Q000,
@@ -1744,6 +1753,12 @@ impl CheckCodePrefix {
             CheckCodePrefix::ICN0 => vec![CheckCode::ICN001],
             CheckCodePrefix::ICN00 => vec![CheckCode::ICN001],
             CheckCodePrefix::ICN001 => vec![CheckCode::ICN001],
+            CheckCodePrefix::ISC => vec![CheckCode::ISC001, CheckCode::ISC002, CheckCode::ISC003],
+            CheckCodePrefix::ISC0 => vec![CheckCode::ISC001, CheckCode::ISC002, CheckCode::ISC003],
+            CheckCodePrefix::ISC00 => vec![CheckCode::ISC001, CheckCode::ISC002, CheckCode::ISC003],
+            CheckCodePrefix::ISC001 => vec![CheckCode::ISC001],
+            CheckCodePrefix::ISC002 => vec![CheckCode::ISC002],
+            CheckCodePrefix::ISC003 => vec![CheckCode::ISC003],
             CheckCodePrefix::M => {
                 one_time_warning!(
                     "{}{} {}",
@@ -3118,6 +3133,12 @@ impl CheckCodePrefix {
             CheckCodePrefix::ICN0 => SuffixLength::One,
             CheckCodePrefix::ICN00 => SuffixLength::Two,
             CheckCodePrefix::ICN001 => SuffixLength::Three,
+            CheckCodePrefix::ISC => SuffixLength::Zero,
+            CheckCodePrefix::ISC0 => SuffixLength::One,
+            CheckCodePrefix::ISC00 => SuffixLength::Two,
+            CheckCodePrefix::ISC001 => SuffixLength::Three,
+            CheckCodePrefix::ISC002 => SuffixLength::Three,
+            CheckCodePrefix::ISC003 => SuffixLength::Three,
             CheckCodePrefix::M => SuffixLength::Zero,
             CheckCodePrefix::M0 => SuffixLength::One,
             CheckCodePrefix::M001 => SuffixLength::Three,
@@ -3386,6 +3407,7 @@ pub const CATEGORIES: &[CheckCodePrefix] = &[
     CheckCodePrefix::FBT,
     CheckCodePrefix::I,
     CheckCodePrefix::ICN,
+    CheckCodePrefix::ISC,
     CheckCodePrefix::N,
     CheckCodePrefix::PD,
     CheckCodePrefix::PGH,

src/flake8_implicit_str_concat/checks.rs

@@ -0,0 +1,73 @@
+use itertools::Itertools;
+use rustpython_ast::{Constant, Expr, ExprKind, Location, Operator};
+use rustpython_parser::lexer::{LexResult, Tok};
+
+use crate::ast::types::Range;
+use crate::checks::{Check, CheckKind};
+use crate::source_code_locator::SourceCodeLocator;
+
+/// ISC001, ISC002
+pub fn implicit(tokens: &[LexResult], locator: &SourceCodeLocator) -> Vec<Check> {
+    let mut checks = vec![];
+    for ((a_start, a_tok, a_end), (b_start, b_tok, b_end)) in
+        tokens.iter().flatten().tuple_windows()
+    {
+        if matches!(a_tok, Tok::String { .. }) && matches!(b_tok, Tok::String { .. }) {
+            if a_end.row() == b_start.row() {
+                checks.push(Check::new(
+                    CheckKind::SingleLineImplicitStringConcatenation,
+                    Range {
+                        location: *a_start,
+                        end_location: *b_end,
+                    },
+                ));
+            } else {
+                // TODO(charlie): The RustPython tokenization doesn't differentiate between
+                // continuations and newlines, so we have to detect them manually.
+                let contents = locator.slice_source_code_range(&Range {
+                    location: *a_end,
+                    end_location: Location::new(a_end.row() + 1, 0),
+                });
+                if contents.trim().ends_with('\\') {
+                    checks.push(Check::new(
+                        CheckKind::MultiLineImplicitStringConcatenation,
+                        Range {
+                            location: *a_start,
+                            end_location: *b_end,
+                        },
+                    ));
+                }
+            }
+        }
+    }
+    checks
+}
+
+/// ISC003
+pub fn explicit(expr: &Expr) -> Option<Check> {
+    if let ExprKind::BinOp { left, op, right } = &expr.node {
+        if matches!(op, Operator::Add) {
+            if matches!(
+                left.node,
+                ExprKind::JoinedStr { .. }
+                    | ExprKind::Constant {
+                        value: Constant::Str(..) | Constant::Bytes(..),
+                        ..
+                    }
+            ) && matches!(
+                right.node,
+                ExprKind::JoinedStr { .. }
+                    | ExprKind::Constant {
+                        value: Constant::Str(..) | Constant::Bytes(..),
+                        ..
+                    }
+            ) {
+                return Some(Check::new(
+                    CheckKind::ExplicitStringConcatenation,
+                    Range::from_located(expr),
+                ));
+            }
+        }
+    }
+    None
+}

src/flake8_implicit_str_concat/mod.rs

@@ -0,0 +1,30 @@
+pub mod checks;
+
+#[cfg(test)]
+mod tests {
+    use std::convert::AsRef;
+    use std::path::Path;
+
+    use anyhow::Result;
+    use test_case::test_case;
+
+    use crate::checks::CheckCode;
+    use crate::linter::test_path;
+    use crate::settings;
+
+    #[test_case(CheckCode::ISC001, Path::new("ISC.py"); "ISC001")]
+    #[test_case(CheckCode::ISC002, Path::new("ISC.py"); "ISC002")]
+    #[test_case(CheckCode::ISC003, Path::new("ISC.py"); "ISC003")]
+    fn checks(check_code: CheckCode, path: &Path) -> Result<()> {
+        let snapshot = format!("{}_{}", check_code.as_ref(), path.to_string_lossy());
+        let mut checks = test_path(
+            Path::new("./resources/test/fixtures/flake8_implicit_str_concat")
+                .join(path)
+                .as_path(),
+            &settings::Settings::for_rule(check_code),
+        )?;
+        checks.sort_by_key(|check| check.location);
+        insta::assert_yaml_snapshot!(snapshot, checks);
+        Ok(())
+    }
+}

src/flake8_implicit_str_concat/snapshots/ruff__flake8_implicit_str_concat__tests__ISC001_ISC.py.snap

@@ -0,0 +1,21 @@
+---
+source: src/flake8_implicit_str_concat/mod.rs
+expression: checks
+---
+- kind: SingleLineImplicitStringConcatenation
+  location:
+    row: 1
+    column: 4
+  end_location:
+    row: 1
+    column: 11
+  fix: ~
+- kind: SingleLineImplicitStringConcatenation
+  location:
+    row: 1
+    column: 8
+  end_location:
+    row: 1
+    column: 15
+  fix: ~
+

src/flake8_implicit_str_concat/snapshots/ruff__flake8_implicit_str_concat__tests__ISC002_ISC.py.snap

@@ -0,0 +1,13 @@
+---
+source: src/flake8_implicit_str_concat/mod.rs
+expression: checks
+---
+- kind: MultiLineImplicitStringConcatenation
+  location:
+    row: 5
+    column: 4
+  end_location:
+    row: 6
+    column: 9
+  fix: ~
+

src/flake8_implicit_str_concat/snapshots/ruff__flake8_implicit_str_concat__tests__ISC003_ISC.py.snap

@@ -0,0 +1,37 @@
+---
+source: src/flake8_implicit_str_concat/mod.rs
+expression: checks
+---
+- kind: ExplicitStringConcatenation
+  location:
+    row: 3
+    column: 4
+  end_location:
+    row: 3
+    column: 17
+  fix: ~
+- kind: ExplicitStringConcatenation
+  location:
+    row: 9
+    column: 2
+  end_location:
+    row: 10
+    column: 7
+  fix: ~
+- kind: ExplicitStringConcatenation
+  location:
+    row: 14
+    column: 2
+  end_location:
+    row: 15
+    column: 7
+  fix: ~
+- kind: ExplicitStringConcatenation
+  location:
+    row: 19
+    column: 2
+  end_location:
+    row: 20
+    column: 8
+  fix: ~
+

src/lib.rs

@@ -39,6 +39,7 @@ mod flake8_comprehensions;
 mod flake8_datetimez;
 mod flake8_debugger;
 pub mod flake8_errmsg;
+mod flake8_implicit_str_concat;
 mod flake8_import_conventions;
 mod flake8_print;
 pub mod flake8_quotes;