[flynt] Use raw triple quotes for joined raw strings with newlines

crates/ruff_linter/resources/test/fixtures/flynt/FLY002.py

@@ -16,7 +16,7 @@
 nok5 = "a".join([choice("flarp")])  # Not OK (not a simple call)
 nok6 = "a".join(x for x in "feefoofum")  # Not OK (generator)
 nok7 = "a".join([f"foo{8}", "bar"])  # Not OK (contains an f-string)
-
+nok8 = '\n'.join([r'line1','line2']) # https://github.com/astral-sh/ruff/issues/19887
 
 # Regression test for: https://github.com/astral-sh/ruff/issues/7197
 def create_file_public_url(url, filename):

crates/ruff_linter/src/rules/flynt/rules/static_join_to_fstring.rs

@@ -2,7 +2,7 @@ use ast::FStringFlags;
 use itertools::Itertools;
 
 use ruff_macros::{ViolationMetadata, derive_message_formats};
-use ruff_python_ast::{self as ast, Arguments, Expr};
+use ruff_python_ast::{self as ast, Arguments, Expr, StringFlags};
 use ruff_text_size::{Ranged, TextRange};
 
 use crate::checkers::ast::Checker;
@@ -72,24 +72,47 @@ fn is_static_length(elts: &[Expr]) -> bool {
 fn build_fstring(joiner: &str, joinees: &[Expr], flags: FStringFlags) -> Option<Expr> {
     // If all elements are string constants, join them into a single string.
     if joinees.iter().all(Expr::is_string_literal_expr) {
-        let mut flags = None;
-        let node = ast::StringLiteral {
-            value: joinees
-                .iter()
-                .filter_map(|expr| {
-                    if let Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) = expr {
-                        if flags.is_none() {
-                            // take the flags from the first Expr
-                            flags = Some(value.first_literal_flags());
-                        }
-                        Some(value.to_str())
-                    } else {
-                        None
+        let mut flags: Option<ast::StringLiteralFlags> = None;
+        let content = joinees
+            .iter()
+            .filter_map(|expr| {
+                if let Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) = expr {
+                    if flags.is_none() {
+                        // Take the flags from the first Expr
+                        flags = Some(value.first_literal_flags());
+                    }
+                    Some(value.to_str())
+                } else {
+                    None
+                }
+            })
+            .join(joiner);
+
+        let mut flags = flags?;
+
+        // If the result is a raw string and contains a newline, use triple quotes.
+        if flags.prefix().is_raw() && (content.contains('\n') || content.contains('\r')) {
+            flags = flags.with_triple_quotes(ruff_python_ast::str::TripleQuotes::Yes);
+
+            // Ensure we pick a safe triple-quote delimiter that doesn't occur in the content.
+            let quote = flags.quote_style();
+            match quote {
+                ruff_python_ast::str::Quote::Single => {
+                    if content.contains("'''") {
+                        flags = flags.with_quote_style(ruff_python_ast::str::Quote::Double);
+                    }
+                }
+                ruff_python_ast::str::Quote::Double => {
+                    if content.contains("\"\"\"") {
+                        flags = flags.with_quote_style(ruff_python_ast::str::Quote::Single);
                     }
-                })
-                .join(joiner)
-                .into_boxed_str(),
-            flags: flags?,
+                }
+            }
+        }
+
+        let node = ast::StringLiteral {
+            value: content.into_boxed_str(),
+            flags,
             range: TextRange::default(),
             node_index: ruff_python_ast::AtomicNodeIndex::NONE,
         };

crates/ruff_linter/src/rules/flynt/snapshots/ruff_linter__rules__flynt__tests__FLY002_FLY002.py.snap

@@ -125,6 +125,28 @@ help: Replace with `f"{secrets.token_urlsafe()}a{secrets.token_hex()}"`
 13 | nok2 = a.join(["1", "2", "3"])  # Not OK (not a static joiner)
 note: This is an unsafe fix and may change runtime behavior
 
+FLY002 [*] Consider f-string instead of string join
+  --> FLY002.py:19:8
+   |
+17 | nok6 = "a".join(x for x in "feefoofum")  # Not OK (generator)
+18 | nok7 = "a".join([f"foo{8}", "bar"])  # Not OK (contains an f-string)
+19 | nok8 = '\n'.join([r'line1','line2']) # https://github.com/astral-sh/ruff/issues/19887
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+20 |
+21 | # Regression test for: https://github.com/astral-sh/ruff/issues/7197
+   |
+help: Replace with f-string
+16 | nok5 = "a".join([choice("flarp")])  # Not OK (not a simple call)
+17 | nok6 = "a".join(x for x in "feefoofum")  # Not OK (generator)
+18 | nok7 = "a".join([f"foo{8}", "bar"])  # Not OK (contains an f-string)
+   - nok8 = '\n'.join([r'line1','line2']) # https://github.com/astral-sh/ruff/issues/19887
+19 + nok8 = r'''line1
+20 + line2''' # https://github.com/astral-sh/ruff/issues/19887
+21 | 
+22 | # Regression test for: https://github.com/astral-sh/ruff/issues/7197
+23 | def create_file_public_url(url, filename):
+note: This is an unsafe fix and may change runtime behavior
+
 FLY002 [*] Consider `f"{url}{filename}"` instead of string join
   --> FLY002.py:23:11
    |