Join implicit concatenated strings when they fit on a line (#13663)

crates/ruff_python_formatter/src/string/docstring.rs

@@ -9,7 +9,7 @@ use std::{borrow::Cow, collections::VecDeque};
 
 use regex::Regex;
 use ruff_formatter::printer::SourceMapGeneration;
-use ruff_python_ast::{str::Quote, StringFlags};
+use ruff_python_ast::{str::Quote, AnyStringFlags, StringFlags};
 use ruff_python_trivia::CommentRanges;
 use {
     ruff_formatter::{write, FormatOptions, IndentStyle, LineWidth, Printed},
@@ -19,7 +19,10 @@ use {
 };
 
 use super::NormalizedString;
-use crate::preview::is_docstring_code_block_in_docstring_indent_enabled;
+use crate::preview::{
+    is_docstring_code_block_in_docstring_indent_enabled,
+    is_join_implicit_concatenated_string_enabled,
+};
 use crate::string::StringQuotes;
 use crate::{prelude::*, DocstringCodeLineWidth, FormatModuleError};
 
@@ -167,7 +170,7 @@ pub(crate) fn format(normalized: &NormalizedString, f: &mut PyFormatter) -> Form
     if docstring[first.len()..].trim().is_empty() {
         // For `"""\n"""` or other whitespace between the quotes, black keeps a single whitespace,
         // but `""""""` doesn't get one inserted.
-        if needs_chaperone_space(normalized, trim_end)
+        if needs_chaperone_space(normalized.flags(), trim_end, f.context())
             || (trim_end.is_empty() && !docstring.is_empty())
         {
             space().fmt(f)?;
@@ -207,7 +210,7 @@ pub(crate) fn format(normalized: &NormalizedString, f: &mut PyFormatter) -> Form
     let trim_end = docstring
         .as_ref()
         .trim_end_matches(|c: char| c.is_whitespace() && c != '\n');
-    if needs_chaperone_space(normalized, trim_end) {
+    if needs_chaperone_space(normalized.flags(), trim_end, f.context()) {
         space().fmt(f)?;
     }
 
@@ -1604,9 +1607,18 @@ fn docstring_format_source(
 /// If the last line of the docstring is `content" """` or `content\ """`, we need a chaperone space
 /// that avoids `content""""` and `content\"""`. This does only applies to un-escaped backslashes,
 /// so `content\\ """` doesn't need a space while `content\\\ """` does.
-fn needs_chaperone_space(normalized: &NormalizedString, trim_end: &str) -> bool {
-    trim_end.ends_with(normalized.flags().quote_style().as_char())
-        || trim_end.chars().rev().take_while(|c| *c == '\\').count() % 2 == 1
+pub(super) fn needs_chaperone_space(
+    flags: AnyStringFlags,
+    trim_end: &str,
+    context: &PyFormatContext,
+) -> bool {
+    if trim_end.chars().rev().take_while(|c| *c == '\\').count() % 2 == 1 {
+        true
+    } else if is_join_implicit_concatenated_string_enabled(context) {
+        flags.is_triple_quoted() && trim_end.ends_with(flags.quote_style().as_char())
+    } else {
+        trim_end.ends_with(flags.quote_style().as_char())
+    }
 }
 
 #[derive(Copy, Clone, Debug)]