Dynamic error location formatting in eldritch-core

implants/lib/eldritchv2/eldritch-core/src/interpreter/core.rs

@@ -224,10 +224,36 @@ impl Interpreter {
         if error.span.line > 0 && error.span.line <= lines.len() {
             let line_idx = error.span.line - 1;
             let line_content = lines[line_idx];
+
+            // Calculate column offset relative to trimmed line
+            let leading_whitespace = line_content.len() - line_content.trim_start().len();
+
+            // Calculate line start byte offset
+            let mut line_start = error.span.start;
+            let source_bytes = source.as_bytes();
+            // Walk backwards from error start to find newline
+            // If error.span.start is beyond source len (shouldn't happen for valid error), clamp it.
+            if line_start > source_bytes.len() {
+                line_start = source_bytes.len();
+            }
+            while line_start > 0 && source_bytes[line_start - 1] != b'\n' {
+                line_start -= 1;
+            }
+
+            // Calculate raw column (byte offset from start of line)
+            let raw_col = error.span.start.saturating_sub(line_start);
+
+            // Calculate display column relative to trimmed string
+            let display_col = raw_col.saturating_sub(leading_whitespace);
+
+            // Create dynamic padding
+            let padding = format!("{:>width$}", "", width = display_col);
+
             output.push_str(&format!(
-                "\n\nError location:\n  at line {}:\n    {}\n    ^-- here",
+                "\n\nError location:\n  at line {}:\n    {}\n    {}^-- here",
                 error.span.line,
-                line_content.trim()
+                line_content.trim(),
+                padding
             ));
         }
         output

implants/lib/eldritchv2/eldritch-core/tests/error_alignment.rs

@@ -0,0 +1,50 @@
+use eldritch_core::Interpreter;
+
+#[test]
+fn test_error_caret_alignment() {
+    let mut interp = Interpreter::new();
+
+    // Test case 1: Error not at start, with indentation
+    // "    x = z + 1"
+    //      ^   ^
+    //      0   4 (relative to trimmed)
+    // In raw string: 4 spaces + 'x' + ' ' + '=' + ' ' + 'z'
+    // 'z' is at index 8.
+    // Trimmed line: "x = z + 1" (starts at index 4)
+    // Error at 8. Relative to trimmed start: 8 - 4 = 4.
+    // Display indent: 4 (base) + 4 (relative) = 8 spaces.
+
+    let code = "    x = z + 1";
+    let res = interp.interpret(code);
+    match res {
+        Ok(_) => panic!("Expected error for 'x = z + 1'"),
+        Err(msg) => {
+            let lines: Vec<&str> = msg.lines().collect();
+            // Expected output:
+            // ...
+            // Error location:
+            //   at line 1:
+            //     x = z + 1
+            //         ^-- here
+
+            let last_line = lines.last().expect("Error message empty");
+            // "        ^-- here"
+            // 8 spaces + ^
+            assert!(last_line.starts_with("        ^-- here"), "Incorrect alignment: '{}'", last_line);
+        }
+    }
+
+    // Test case 2: Error at start of trimmed line
+    // Just accessing undefined 'z'
+    let code2 = "    z";
+    let res2 = interp.interpret(code2);
+    match res2 {
+        Ok(_) => panic!("Expected error for 'z'"),
+        Err(msg) => {
+            let lines: Vec<&str> = msg.lines().collect();
+            let last_line = lines.last().expect("Error message empty");
+            // "    ^-- here" (4 spaces indent)
+            assert!(last_line.starts_with("    ^-- here"), "Incorrect alignment for start of line: '{}'", last_line);
+        }
+    }
+}