prevent panic with format command (#7522)

Related: #7211.

Prevents numeric underflow in span.

Co-authored-by: sholderbach <sholderbach@users.noreply.github.com>

crates/nu-command/src/strings/format/command.rs

@@ -55,7 +55,11 @@ impl Command for Format {
                 let string_span = pattern.span()?;
                 // the string span is start as `"`, we don't need the character
                 // to generate proper span for sub expression.
-                let ops = extract_formatting_operations(string_pattern, string_span.start + 1);
+                let ops = extract_formatting_operations(
+                    string_pattern,
+                    call.head,
+                    string_span.start + 1,
+                )?;
 
                 format(
                     input_val,
@@ -112,7 +116,11 @@ enum FormatOperation {
 /// formatted according to the input pattern.
 /// FormatOperation::ValueNeedEval contains expression which need to eval, it has the following form:
 /// "$it.column1.column2" or "$variable"
-fn extract_formatting_operations(input: String, span_start: usize) -> Vec<FormatOperation> {
+fn extract_formatting_operations(
+    input: String,
+    error_span: Span,
+    span_start: usize,
+) -> Result<Vec<FormatOperation>, ShellError> {
     let mut output = vec![];
 
     let mut characters = input.char_indices();
@@ -148,6 +156,13 @@ fn extract_formatting_operations(input: String, span_start: usize) -> Vec<Format
             column_name.push(ch);
         }
 
+        if column_span_end < column_span_start {
+            return Err(ShellError::DelimiterError(
+                "there are unmatched curly braces".to_string(),
+                error_span,
+            ));
+        }
+
         if !column_name.is_empty() {
             if column_need_eval {
                 output.push(FormatOperation::ValueNeedEval(
@@ -166,7 +181,7 @@ fn extract_formatting_operations(input: String, span_start: usize) -> Vec<Format
             break;
         }
     }
-    output
+    Ok(output)
 }
 
 /// Format the incoming PipelineData according to the pattern

crates/nu-command/tests/commands/format.rs

@@ -42,6 +42,19 @@ fn can_use_variables() {
     assert_eq!(actual.out, "nu is a new type of shell");
 }
 
+#[test]
+fn error_unmatched_brace() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+        open cargo_sample.toml
+            | format "{$it.package.name"
+        "#
+    ));
+
+    assert!(actual.err.contains("unmatched curly brace"));
+}
+
 #[test]
 fn format_filesize_works() {
     Playground::setup("format_filesize_test_1", |dirs, sandbox| {