Fix invalid printer IR error (#5422)

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/string.py

@@ -108,3 +108,13 @@ test_particular = [
     '1.0000000000000000000000000000000000000000000010000' #...
     '0000000000000000000000000000000000000000025',
 ]
+
+# Parenthesized string continuation with messed up indentation
+{
+    "key": (
+        [],
+    'a'
+        'b'
+    'c'
+    )
+}

crates/ruff_python_formatter/src/builders.rs

@@ -242,6 +242,7 @@ impl<'fmt, 'ast, 'buf> JoinCommaSeparatedBuilder<'fmt, 'ast, 'buf> {
     }
 
     pub(crate) fn finish(&mut self) -> FormatResult<()> {
+        self.result.and_then(|_| {
             if let Some(last_end) = self.last_end.take() {
                 if_group_breaks(&text(",")).fmt(self.fmt)?;
 
@@ -259,6 +260,7 @@ impl<'fmt, 'ast, 'buf> JoinCommaSeparatedBuilder<'fmt, 'ast, 'buf> {
             }
 
             Ok(())
+        })
     }
 }
 

crates/ruff_python_formatter/src/expression/string.rs

@@ -8,7 +8,7 @@ use ruff_formatter::{format_args, write, FormatError};
 use ruff_python_ast::str::is_implicit_concatenation;
 use ruff_text_size::{TextLen, TextRange, TextSize};
 use rustpython_parser::ast::{ExprConstant, Ranged};
-use rustpython_parser::lexer::lex_starts_at;
+use rustpython_parser::lexer::{lex_starts_at, LexicalError, LexicalErrorType};
 use rustpython_parser::{Mode, Tok};
 use std::borrow::Cow;
 
@@ -83,7 +83,7 @@ impl Format<PyFormatContext<'_>> for FormatStringContinuation<'_> {
         // Call into the lexer to extract the individual chunks and format each string on its own.
         // This code does not yet implement the automatic joining of strings that fit on the same line
         // because this is a black preview style.
-        let lexer = lex_starts_at(string_content, Mode::Module, string_range.start());
+        let lexer = lex_starts_at(string_content, Mode::Expression, string_range.start());
 
         let separator = format_with(|f| match self.layout {
             StringLayout::Default(_) => soft_line_break_or_space().fmt(f),
@@ -93,7 +93,31 @@ impl Format<PyFormatContext<'_>> for FormatStringContinuation<'_> {
         let mut joiner = f.join_with(separator);
 
         for token in lexer {
-            let (token, token_range) = token.map_err(|_| FormatError::SyntaxError)?;
+            let (token, token_range) = match token {
+                Ok(spanned) => spanned,
+                Err(LexicalError {
+                    error: LexicalErrorType::IndentationError,
+                    ..
+                }) => {
+                    // This can happen if the string continuation appears anywhere inside of a parenthesized expression
+                    // because the lexer doesn't know about the parentheses. For example, the following snipped triggers an Indentation error
+                    // ```python
+                    // {
+                    //     "key": (
+                    //         [],
+                    //         'a'
+                    //             'b'
+                    //          'c'
+                    //     )
+                    // }
+                    // ```
+                    // Ignoring the error here is *safe* because we know that the program once parsed to a valid AST.
+                    continue;
+                }
+                Err(_) => {
+                    return Err(FormatError::SyntaxError);
+                }
+            };
 
             match token {
                 Tok::String { .. } => {

crates/ruff_python_formatter/tests/snapshots/format@expression__string.py.snap

@@ -114,6 +114,16 @@ test_particular = [
     '1.0000000000000000000000000000000000000000000010000' #...
     '0000000000000000000000000000000000000000025',
 ]
+
+# Parenthesized string continuation with messed up indentation
+{
+    "key": (
+        [],
+    'a'
+        'b'
+    'c'
+    )
+}
 ```
 
 ## Outputs
@@ -259,6 +269,9 @@ test_particular = [
     "1.0000000000000000000000000000000000000000000010000"  # ...
     "0000000000000000000000000000000000000000025",
 ]
+
+# Parenthesized string continuation with messed up indentation
+{"key": ([], "a" "b" "c")}
 ```
 
 
@@ -404,6 +417,9 @@ test_particular = [
     '1.0000000000000000000000000000000000000000000010000'  # ...
     '0000000000000000000000000000000000000000025',
 ]
+
+# Parenthesized string continuation with messed up indentation
+{'key': ([], 'a' 'b' 'c')}
 ```