fix: properly format prompt retrieval error messages from MCP (#216)

Author: jbshu4546

crates/chat-cli/src/cli/chat/cli/prompts.rs

@@ -19,6 +19,7 @@ use crossterm::{
 use thiserror::Error;
 use unicode_width::UnicodeWidthStr;
 
+use crate::cli::chat::error_formatter::format_mcp_error;
 use crate::cli::chat::tool_manager::PromptBundle;
 use crate::cli::chat::{
     ChatError,
@@ -278,9 +279,7 @@ impl PromptsSubcommand {
                 style::SetAttribute(Attribute::Reset),
                 style::Print("\n"),
                 style::SetForegroundColor(Color::Red),
-                style::Print(
-                    serde_json::to_string_pretty(&to_display).unwrap_or_else(|_| format!("{:?}", &to_display))
-                ),
+                style::Print(format_mcp_error(&to_display)),
                 style::SetForegroundColor(Color::Reset),
                 style::Print("\n"),
             )?;

crates/chat-cli/src/cli/chat/error_formatter.rs

@@ -0,0 +1,148 @@
+/// Formats an MCP error message to be more user-friendly.
+///
+/// This function extracts nested JSON from the error message and formats it
+/// with proper indentation and newlines.
+///
+/// # Arguments
+///
+/// * `err` - A reference to a serde_json::Value containing the error information
+///
+/// # Returns
+///
+/// A formatted string representation of the error message
+pub fn format_mcp_error(err: &serde_json::Value) -> String {
+    // Extract the message field from the error JSON
+    if let Some(message) = err.get("message").and_then(|m| m.as_str()) {
+        // Check if the message contains a nested JSON array
+        if let Some(start_idx) = message.find('[') {
+            if let Some(end_idx) = message.rfind(']') {
+                let prefix = &message[..start_idx].trim();
+                let nested_json = &message[start_idx..=end_idx];
+
+                // Try to parse the nested JSON
+                if let Ok(nested_value) = serde_json::from_str::<serde_json::Value>(nested_json) {
+                    // Format the error message with the prefix and pretty-printed nested JSON
+                    return format!(
+                        "{}\n{}",
+                        prefix,
+                        serde_json::to_string_pretty(&nested_value).unwrap_or_else(|_| nested_json.to_string())
+                    );
+                }
+            }
+        }
+    }
+
+    // Fallback if message field is missing or if we couldn't extract and parse nested JSON
+    serde_json::to_string_pretty(err).unwrap_or_else(|_| format!("{:?}", err))
+}
+
+#[cfg(test)]
+mod tests {
+    use serde_json::json;
+
+    use super::*;
+
+    #[test]
+    fn test_format_mcp_error_with_nested_json() {
+        let error = json!({
+            "code": -32602,
+            "message": "MCP error -32602: Invalid arguments for prompt agent_script_coco_was_sev2_ticket_details_retrieve: [\n  {\n    \"code\": \"invalid_type\",\n    \"expected\": \"object\",\n    \"received\": \"undefined\",\n    \"path\": [],\n    \"message\": \"Required\"\n  }\n]"
+        });
+
+        let formatted = format_mcp_error(&error);
+
+        // Extract the prefix and JSON part from the formatted string
+        let parts: Vec<&str> = formatted.split('\n').collect();
+        let prefix = parts[0];
+        let json_part = &formatted[prefix.len() + 1..];
+
+        // Check that the prefix is correct
+        assert_eq!(
+            prefix,
+            "MCP error -32602: Invalid arguments for prompt agent_script_coco_was_sev2_ticket_details_retrieve:"
+        );
+
+        // Parse the JSON part to compare the actual content rather than the exact string
+        let parsed_json: serde_json::Value = serde_json::from_str(json_part).expect("Failed to parse JSON part");
+
+        // Expected JSON structure
+        let expected_json = json!([
+            {
+                "code": "invalid_type",
+                "expected": "object",
+                "received": "undefined",
+                "path": [],
+                "message": "Required"
+            }
+        ]);
+
+        // Compare the parsed JSON values
+        assert_eq!(parsed_json, expected_json);
+    }
+
+    #[test]
+    fn test_format_mcp_error_without_nested_json() {
+        let error = json!({
+            "code": -32602,
+            "message": "MCP error -32602: Invalid arguments for prompt"
+        });
+
+        let formatted = format_mcp_error(&error);
+
+        assert_eq!(
+            formatted,
+            "{\n  \"code\": -32602,\n  \"message\": \"MCP error -32602: Invalid arguments for prompt\"\n}"
+        );
+    }
+
+    #[test]
+    fn test_format_mcp_error_non_mcp_error() {
+        let error = json!({
+            "error": "Unknown error occurred"
+        });
+
+        let formatted = format_mcp_error(&error);
+
+        // Should pretty-print the entire error
+        assert_eq!(formatted, "{\n  \"error\": \"Unknown error occurred\"\n}");
+    }
+
+    #[test]
+    fn test_format_mcp_error_empty_message() {
+        let error = json!({
+            "code": -32602,
+            "message": ""
+        });
+
+        let formatted = format_mcp_error(&error);
+
+        assert_eq!(formatted, "{\n  \"code\": -32602,\n  \"message\": \"\"\n}");
+    }
+
+    #[test]
+    fn test_format_mcp_error_missing_message() {
+        let error = json!({
+            "code": -32602
+        });
+
+        let formatted = format_mcp_error(&error);
+
+        assert_eq!(formatted, "{\n  \"code\": -32602\n}");
+    }
+
+    #[test]
+    fn test_format_mcp_error_malformed_nested_json() {
+        let error = json!({
+            "code": -32602,
+            "message": "MCP error -32602: Invalid arguments for prompt: [{\n  \"code\": \"invalid_type\",\n  \"expected\": \"object\",\n  \"received\": \"undefined\",\n  \"path\": [],\n  \"message\": \"Required\"\n"
+        });
+
+        let formatted = format_mcp_error(&error);
+
+        // Should return the pretty-printed JSON since the nested JSON is malformed
+        assert_eq!(
+            formatted,
+            "{\n  \"code\": -32602,\n  \"message\": \"MCP error -32602: Invalid arguments for prompt: [{\\n  \\\"code\\\": \\\"invalid_type\\\",\\n  \\\"expected\\\": \\\"object\\\",\\n  \\\"received\\\": \\\"undefined\\\",\\n  \\\"path\\\": [],\\n  \\\"message\\\": \\\"Required\\\"\\n\"\n}"
+        );
+    }
+}

crates/chat-cli/src/cli/chat/mod.rs

@@ -2,6 +2,7 @@ mod cli;
 mod consts;
 mod context;
 mod conversation;
+mod error_formatter;
 mod input_source;
 mod message;
 mod parse;