Fix regression causing crash indenting commandline with "$()"

Commit b00899179f (Don't indent multi-line quoted strings; do indent inside
(), 2024-04-28) changed how we compute indents for string tokens with command
substitutions:

	echo "begin
	not indented
	end $(
	begin
	    indented
	end)"(
	begin
	    indented
	end
	)

For the leading quoted part of the string, we compute indentation only for
the first character (the opening quote), see 4c43819d32 (Fix crash indenting
quoted suffix after command substitution, 2024-09-28).

The command substitutions, we do indent as usual.

To implement the above, we need to separate quoted from non-quoted
parts. This logic crashes when indent_string_part() is wrongly passed
is_double_quoted=true.

This is because, given the string "$()"$(), parse_util_locate_cmdsub calls
quote_end() at index 4 (the second quote). This is wrong because that function
should only be called at opening quotes; this is a closing quote. The opening
quote is virtual here. Hack around this.

Fixes #11444

(cherry picked from commit 48704dc612)

src/parse_util.rs

@@ -227,13 +227,16 @@ fn process_opening_quote(
         inout_is_quoted: &mut Option<&mut bool>,
         paran_count: i32,
         quoted_cmdsubs: &mut Vec<i32>,
-        pos: usize,
+        mut pos: usize,
         last_dollar: &mut Option<usize>,
         quote: Quote,
     ) -> Option<usize> {
         let quote = match quote {
             Quote::Real(q) => q,
-            Quote::VirtualDouble => '"',
+            Quote::VirtualDouble => {
+                pos = pos.saturating_sub(1);
+                '"'
+            }
         };
         let q_end = quote_end(input.into(), pos, quote)?;
         // Found a valid closing quote.
@@ -266,7 +269,7 @@ fn process_opening_quote(
             &mut last_dollar,
             Quote::VirtualDouble,
         )
-        .unwrap_or(input.len());
+        .map_or(input.len(), |pos| pos + 1);
     }
 
     while pos < input.len() {

src/tests/parse_util.rs

@@ -439,5 +439,10 @@ macro_rules! validate {
             0, r#"echo "$()"'"#,
             0, "\n"
         );
+        validate!(
+            0, r#"""#,
+            0, "\n",
+            0, r#"$()"$() ""#
+        );
     })();
 }