New rule to prevent implicit string concatenation in collections

_typos.toml

@@ -4,6 +4,7 @@ extend-exclude = [
     "crates/ty_vendored/vendor/**/*",
     "**/resources/**/*",
     "**/snapshots/**/*",
+    "crates/ruff_linter/src/rules/flake8_implicit_str_concat/rules/collection_literal.rs",
     # Completion tests tend to have a lot of incomplete
     # words naturally. It's annoying to have to make all
     # of them actually words. So just ignore typos here.

crates/ruff_linter/resources/test/fixtures/flake8_implicit_str_concat/ISC004.py

@@ -0,0 +1,66 @@
+facts = (
+    "Lobsters have blue blood.",
+    "The liver is the only human organ that can fully regenerate itself.",
+    "Clarinets are made almost entirely out of wood from the mpingo tree."
+    "In 1971, astronaut Alan Shepard played golf on the moon.",
+)
+
+facts = [
+    "Lobsters have blue blood.",
+    "The liver is the only human organ that can fully regenerate itself.",
+    "Clarinets are made almost entirely out of wood from the mpingo tree."
+    "In 1971, astronaut Alan Shepard played golf on the moon.",
+]
+
+facts = {
+    "Lobsters have blue blood.",
+    "The liver is the only human organ that can fully regenerate itself.",
+    "Clarinets are made almost entirely out of wood from the mpingo tree."
+    "In 1971, astronaut Alan Shepard played golf on the moon.",
+}
+
+facts = {
+    (
+        "Clarinets are made almost entirely out of wood from the mpingo tree."
+        "In 1971, astronaut Alan Shepard played golf on the moon."
+    ),
+}
+
+facts = (
+    "Octopuses have three hearts."
+    # Missing comma here.
+    "Honey never spoils.",
+)
+
+facts = [
+    "Octopuses have three hearts."
+    # Missing comma here.
+    "Honey never spoils.",
+]
+
+facts = {
+    "Octopuses have three hearts."
+    # Missing comma here.
+    "Honey never spoils.",
+}
+
+facts = (
+    (
+        "Clarinets are made almost entirely out of wood from the mpingo tree."
+        "In 1971, astronaut Alan Shepard played golf on the moon."
+    ),
+)
+
+facts = [
+    (
+        "Clarinets are made almost entirely out of wood from the mpingo tree."
+        "In 1971, astronaut Alan Shepard played golf on the moon."
+    ),
+]
+
+facts = (
+    "Lobsters have blue blood.\n"
+    "The liver is the only human organ that can fully regenerate itself.\n"
+    "Clarinets are made almost entirely out of wood from the mpingo tree.\n"
+    "In 1971, astronaut Alan Shepard played golf on the moon.\n"
+)

crates/ruff_linter/src/checkers/ast/analyze/expression.rs

@@ -214,6 +214,13 @@ pub(crate) fn expression(expr: &Expr, checker: &Checker) {
             range: _,
             node_index: _,
         }) => {
+            if checker.is_rule_enabled(Rule::ImplicitStringConcatenationInCollectionLiteral) {
+                flake8_implicit_str_concat::rules::implicit_string_concatenation_in_collection_literal(
+                    checker,
+                    expr,
+                    elts,
+                );
+            }
             if ctx.is_store() {
                 let check_too_many_expressions =
                     checker.is_rule_enabled(Rule::ExpressionsInStarAssignment);
@@ -1329,6 +1336,13 @@ pub(crate) fn expression(expr: &Expr, checker: &Checker) {
             }
         }
         Expr::Set(set) => {
+            if checker.is_rule_enabled(Rule::ImplicitStringConcatenationInCollectionLiteral) {
+                flake8_implicit_str_concat::rules::implicit_string_concatenation_in_collection_literal(
+                    checker,
+                    expr,
+                    &set.elts,
+                );
+            }
             if checker.is_rule_enabled(Rule::DuplicateValue) {
                 flake8_bugbear::rules::duplicate_value(checker, set);
             }

crates/ruff_linter/src/codes.rs

@@ -454,6 +454,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8ImplicitStrConcat, "001") => rules::flake8_implicit_str_concat::rules::SingleLineImplicitStringConcatenation,
         (Flake8ImplicitStrConcat, "002") => rules::flake8_implicit_str_concat::rules::MultiLineImplicitStringConcatenation,
         (Flake8ImplicitStrConcat, "003") => rules::flake8_implicit_str_concat::rules::ExplicitStringConcatenation,
+        (Flake8ImplicitStrConcat, "004") => rules::flake8_implicit_str_concat::rules::ImplicitStringConcatenationInCollectionLiteral,
 
         // flake8-print
         (Flake8Print, "1") => rules::flake8_print::rules::Print,

crates/ruff_linter/src/rules/flake8_implicit_str_concat/mod.rs

@@ -32,6 +32,10 @@ mod tests {
         Path::new("ISC_syntax_error_2.py")
     )]
     #[test_case(Rule::ExplicitStringConcatenation, Path::new("ISC.py"))]
+    #[test_case(
+        Rule::ImplicitStringConcatenationInCollectionLiteral,
+        Path::new("ISC004.py")
+    )]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
         let diagnostics = test_path(

crates/ruff_linter/src/rules/flake8_implicit_str_concat/rules/collection_literal.rs

@@ -0,0 +1,103 @@
+use ruff_macros::{ViolationMetadata, derive_message_formats};
+use ruff_python_ast::token::parenthesized_range;
+use ruff_python_ast::{Expr, StringLike};
+use ruff_text_size::Ranged;
+
+use crate::checkers::ast::Checker;
+use crate::{Edit, Fix, FixAvailability, Violation};
+
+/// ## What it does
+/// Checks for implicitly concatenated strings inside list, tuple, and set literals.
+///
+/// ## Why is this bad?
+/// In collection literals, implicit string concatenation is often the result of
+/// a missing comma between elements, which can silently merge items together.
+///
+/// ## Example
+/// ```python
+/// facts = (
+///     "Lobsters have blue blood.",
+///     "The liver is the only human organ that can fully regenerate itself.",
+///     "Clarinets are made almost entirely out of wood from the mpingo tree."
+///     "In 1971, astronaut Alan Shepard played golf on the moon.",
+/// )
+/// ```
+///
+/// Instead, you likely intended:
+/// ```python
+/// facts = (
+///     "Lobsters have blue blood.",
+///     "The liver is the only human organ that can fully regenerate itself.",
+///     "Clarinets are made almost entirely out of wood from the mpingo tree.",
+///     "In 1971, astronaut Alan Shepard played golf on the moon.",
+/// )
+/// ```
+///
+/// If the concatenation is intentional, wrap it in parentheses to make it
+/// explicit:
+/// ```python
+/// facts = (
+///     "Lobsters have blue blood.",
+///     "The liver is the only human organ that can fully regenerate itself.",
+///     (
+///         "Clarinets are made almost entirely out of wood from the mpingo tree."
+///         "In 1971, astronaut Alan Shepard played golf on the moon."
+///     ),
+/// )
+/// ```
+///
+/// ## Fix safety
+/// The fix is safe in that it does not change the semantics of your code.
+/// However, the issue is that you may often want to change semantics
+/// by adding a missing comma.
+#[derive(ViolationMetadata)]
+#[violation_metadata(preview_since = "0.14.10")]
+pub(crate) struct ImplicitStringConcatenationInCollectionLiteral;
+
+impl Violation for ImplicitStringConcatenationInCollectionLiteral {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Always;
+
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        "Unparenthesized implicit string concatenation in collection".to_string()
+    }
+
+    fn fix_title(&self) -> Option<String> {
+        Some("Wrap implicitly concatenated strings in parentheses".to_string())
+    }
+}
+
+/// ISC004
+pub(crate) fn implicit_string_concatenation_in_collection_literal(
+    checker: &Checker,
+    expr: &Expr,
+    elements: &[Expr],
+) {
+    for element in elements {
+        let Ok(string_like) = StringLike::try_from(element) else {
+            continue;
+        };
+        if !string_like.is_implicit_concatenated() {
+            continue;
+        }
+        if parenthesized_range(
+            string_like.as_expression_ref(),
+            expr.into(),
+            checker.tokens(),
+        )
+        .is_some()
+        {
+            continue;
+        }
+
+        let mut diagnostic = checker.report_diagnostic(
+            ImplicitStringConcatenationInCollectionLiteral,
+            string_like.range(),
+        );
+        diagnostic.help("Did you forget a comma?");
+        diagnostic.set_fix(Fix::unsafe_edits(
+            Edit::insertion("(".to_string(), string_like.range().start()),
+            [Edit::insertion(")".to_string(), string_like.range().end())],
+        ));
+    }
+}

crates/ruff_linter/src/rules/flake8_implicit_str_concat/rules/mod.rs

@@ -1,5 +1,7 @@
+pub(crate) use collection_literal::*;
 pub(crate) use explicit::*;
 pub(crate) use implicit::*;
 
+mod collection_literal;
 mod explicit;
 mod implicit;

crates/ruff_linter/src/rules/flake8_implicit_str_concat/snapshots/ruff_linter__rules__flake8_implicit_str_concat__tests__ISC004_ISC004.py.snap

@@ -0,0 +1,149 @@
+---
+source: crates/ruff_linter/src/rules/flake8_implicit_str_concat/mod.rs
+---
+ISC004 [*] Unparenthesized implicit string concatenation in collection
+ --> ISC004.py:4:5
+  |
+2 |       "Lobsters have blue blood.",
+3 |       "The liver is the only human organ that can fully regenerate itself.",
+4 | /     "Clarinets are made almost entirely out of wood from the mpingo tree."
+5 | |     "In 1971, astronaut Alan Shepard played golf on the moon.",
+  | |______________________________________________________________^
+6 |   )
+  |
+help: Wrap implicitly concatenated strings in parentheses
+help: Did you forget a comma?
+1 | facts = (
+2 |     "Lobsters have blue blood.",
+3 |     "The liver is the only human organ that can fully regenerate itself.",
+  -     "Clarinets are made almost entirely out of wood from the mpingo tree."
+  -     "In 1971, astronaut Alan Shepard played golf on the moon.",
+4 +     ("Clarinets are made almost entirely out of wood from the mpingo tree."
+5 +     "In 1971, astronaut Alan Shepard played golf on the moon."),
+6 | )
+7 | 
+8 | facts = [
+note: This is an unsafe fix and may change runtime behavior
+
+ISC004 [*] Unparenthesized implicit string concatenation in collection
+  --> ISC004.py:11:5
+   |
+ 9 |       "Lobsters have blue blood.",
+10 |       "The liver is the only human organ that can fully regenerate itself.",
+11 | /     "Clarinets are made almost entirely out of wood from the mpingo tree."
+12 | |     "In 1971, astronaut Alan Shepard played golf on the moon.",
+   | |______________________________________________________________^
+13 |   ]
+   |
+help: Wrap implicitly concatenated strings in parentheses
+help: Did you forget a comma?
+8  | facts = [
+9  |     "Lobsters have blue blood.",
+10 |     "The liver is the only human organ that can fully regenerate itself.",
+   -     "Clarinets are made almost entirely out of wood from the mpingo tree."
+   -     "In 1971, astronaut Alan Shepard played golf on the moon.",
+11 +     ("Clarinets are made almost entirely out of wood from the mpingo tree."
+12 +     "In 1971, astronaut Alan Shepard played golf on the moon."),
+13 | ]
+14 | 
+15 | facts = {
+note: This is an unsafe fix and may change runtime behavior
+
+ISC004 [*] Unparenthesized implicit string concatenation in collection
+  --> ISC004.py:18:5
+   |
+16 |       "Lobsters have blue blood.",
+17 |       "The liver is the only human organ that can fully regenerate itself.",
+18 | /     "Clarinets are made almost entirely out of wood from the mpingo tree."
+19 | |     "In 1971, astronaut Alan Shepard played golf on the moon.",
+   | |______________________________________________________________^
+20 |   }
+   |
+help: Wrap implicitly concatenated strings in parentheses
+help: Did you forget a comma?
+15 | facts = {
+16 |     "Lobsters have blue blood.",
+17 |     "The liver is the only human organ that can fully regenerate itself.",
+   -     "Clarinets are made almost entirely out of wood from the mpingo tree."
+   -     "In 1971, astronaut Alan Shepard played golf on the moon.",
+18 +     ("Clarinets are made almost entirely out of wood from the mpingo tree."
+19 +     "In 1971, astronaut Alan Shepard played golf on the moon."),
+20 | }
+21 | 
+22 | facts = {
+note: This is an unsafe fix and may change runtime behavior
+
+ISC004 [*] Unparenthesized implicit string concatenation in collection
+  --> ISC004.py:30:5
+   |
+29 |   facts = (
+30 | /     "Octopuses have three hearts."
+31 | |     # Missing comma here.
+32 | |     "Honey never spoils.",
+   | |_________________________^
+33 |   )
+   |
+help: Wrap implicitly concatenated strings in parentheses
+help: Did you forget a comma?
+27 | }
+28 | 
+29 | facts = (
+   -     "Octopuses have three hearts."
+30 +     ("Octopuses have three hearts."
+31 |     # Missing comma here.
+   -     "Honey never spoils.",
+32 +     "Honey never spoils."),
+33 | )
+34 | 
+35 | facts = [
+note: This is an unsafe fix and may change runtime behavior
+
+ISC004 [*] Unparenthesized implicit string concatenation in collection
+  --> ISC004.py:36:5
+   |
+35 |   facts = [
+36 | /     "Octopuses have three hearts."
+37 | |     # Missing comma here.
+38 | |     "Honey never spoils.",
+   | |_________________________^
+39 |   ]
+   |
+help: Wrap implicitly concatenated strings in parentheses
+help: Did you forget a comma?
+33 | )
+34 | 
+35 | facts = [
+   -     "Octopuses have three hearts."
+36 +     ("Octopuses have three hearts."
+37 |     # Missing comma here.
+   -     "Honey never spoils.",
+38 +     "Honey never spoils."),
+39 | ]
+40 | 
+41 | facts = {
+note: This is an unsafe fix and may change runtime behavior
+
+ISC004 [*] Unparenthesized implicit string concatenation in collection
+  --> ISC004.py:42:5
+   |
+41 |   facts = {
+42 | /     "Octopuses have three hearts."
+43 | |     # Missing comma here.
+44 | |     "Honey never spoils.",
+   | |_________________________^
+45 |   }
+   |
+help: Wrap implicitly concatenated strings in parentheses
+help: Did you forget a comma?
+39 | ]
+40 | 
+41 | facts = {
+   -     "Octopuses have three hearts."
+42 +     ("Octopuses have three hearts."
+43 |     # Missing comma here.
+   -     "Honey never spoils.",
+44 +     "Honey never spoils."),
+45 | }
+46 | 
+47 | facts = (
+note: This is an unsafe fix and may change runtime behavior